From b8d1271bc07dc4cefc911ca1e9f3fd7348481403 Mon Sep 17 00:00:00 2001
From: Bet4 <0xbet4@gmail.com>
Date: Fri, 17 Sep 2021 11:55:33 +0800
Subject: [PATCH 1/7] Pass PacketBuf as an argument of API

---
 examples/armv4t/gdb/host_io.rs                | 57 ++++++++++---------
 examples/armv4t/gdb/memory_map.rs             | 18 +++++-
 .../gdb/target_description_xml_override.rs    | 18 +++++-
 src/gdbstub_impl/ext/base.rs                  | 33 +++++++----
 src/gdbstub_impl/ext/host_io.rs               | 48 ++++------------
 src/gdbstub_impl/ext/memory_map.rs            | 12 +++-
 src/protocol/commands.rs                      |  6 +-
 src/protocol/commands/_qXfer_features_read.rs | 19 ++++---
 src/protocol/commands/_qXfer_memory_map.rs    | 19 ++++---
 src/protocol/commands/_vFile_pread.rs         | 19 +++++--
 src/protocol/commands/_vFile_readlink.rs      |  8 ++-
 src/protocol/response_writer.rs               | 19 -------
 src/target/ext/host_io.rs                     | 38 ++-----------
 src/target/ext/memory_map.rs                  |  9 ++-
 .../ext/target_description_xml_override.rs    |  9 ++-
 15 files changed, 170 insertions(+), 162 deletions(-)

diff --git a/examples/armv4t/gdb/host_io.rs b/examples/armv4t/gdb/host_io.rs
index a3a6e3f1..74f2703a 100644
--- a/examples/armv4t/gdb/host_io.rs
+++ b/examples/armv4t/gdb/host_io.rs
@@ -2,8 +2,7 @@ use std::io::{Read, Seek, Write};
 
 use gdbstub::target;
 use gdbstub::target::ext::host_io::{
-    FsKind, HostIoErrno, HostIoError, HostIoOpenFlags, HostIoOpenMode, HostIoOutput, HostIoResult,
-    HostIoStat, HostIoToken,
+    FsKind, HostIoErrno, HostIoError, HostIoOpenFlags, HostIoOpenMode, HostIoResult, HostIoStat,
 };
 
 use crate::emu::Emu;
@@ -133,16 +132,18 @@ impl target::ext::host_io::HostIoPread for Emu {
     fn pread<'a>(
         &mut self,
         fd: u32,
-        count: u32,
-        offset: u32,
-        output: HostIoOutput<'a>,
-    ) -> HostIoResult<HostIoToken<'a>, Self> {
+        count: usize,
+        offset: u64,
+        buf: &mut [u8],
+    ) -> HostIoResult<usize, Self> {
         if fd < FD_RESERVED {
             if fd == 0 {
                 let len = TEST_PROGRAM_ELF.len();
-                return Ok(output.write(
-                    &TEST_PROGRAM_ELF[len.min(offset as usize)..len.min((offset + count) as usize)],
-                ));
+                let data =
+                    &TEST_PROGRAM_ELF[len.min(offset as usize)..len.min(offset as usize + count)];
+                let buf = &mut buf[..data.len()];
+                buf.copy_from_slice(data);
+                return Ok(data.len());
             } else {
                 return Err(HostIoError::Errno(HostIoErrno::EBADF));
             }
@@ -153,10 +154,9 @@ impl target::ext::host_io::HostIoPread for Emu {
             _ => return Err(HostIoError::Errno(HostIoErrno::EBADF)),
         };
 
-        let mut buffer = vec![0; count as usize];
-        file.seek(std::io::SeekFrom::Start(offset as u64))?;
-        let n = file.read(&mut buffer)?;
-        Ok(output.write(&buffer[..n]))
+        file.seek(std::io::SeekFrom::Start(offset))?;
+        let n = file.read(buf)?;
+        Ok(n)
     }
 }
 
@@ -246,29 +246,34 @@ impl target::ext::host_io::HostIoUnlink for Emu {
 }
 
 impl target::ext::host_io::HostIoReadlink for Emu {
-    fn readlink<'a>(
-        &mut self,
-        filename: &[u8],
-        output: HostIoOutput<'a>,
-    ) -> HostIoResult<HostIoToken<'a>, Self> {
+    fn readlink<'a>(&mut self, filename: &[u8], buf: &mut [u8]) -> HostIoResult<usize, Self> {
         if filename == b"/proc/1/exe" {
             // Support `info proc exe` command
-            return Ok(output.write(b"/test.elf"));
+            let exe = b"/test.elf";
+            let buf = &mut buf[..exe.len()];
+            buf.copy_from_slice(exe);
+            return Ok(exe.len());
         } else if filename == b"/proc/1/cwd" {
             // Support `info proc cwd` command
-            return Ok(output.write(b"/"));
+            let cwd = b"/";
+            let buf = &mut buf[..cwd.len()];
+            buf.copy_from_slice(cwd);
+            return Ok(cwd.len());
         } else if filename.starts_with(b"/proc") {
             return Err(HostIoError::Errno(HostIoErrno::ENOENT));
         }
 
         let path =
             std::str::from_utf8(filename).map_err(|_| HostIoError::Errno(HostIoErrno::ENOENT))?;
-        Ok(output.write(
-            std::fs::read_link(path)?
-                .to_str()
-                .ok_or(HostIoError::Errno(HostIoErrno::ENOENT))?
-                .as_bytes(),
-        ))
+        let link = std::fs::read_link(path)?;
+        let data = link
+            .to_str()
+            .ok_or(HostIoError::Errno(HostIoErrno::ENOENT))?
+            .as_bytes();
+        let len = data.len();
+        let buf = &mut buf[..len];
+        buf.copy_from_slice(data);
+        Ok(len)
     }
 }
 
diff --git a/examples/armv4t/gdb/memory_map.rs b/examples/armv4t/gdb/memory_map.rs
index a9e29a9e..82d26a1d 100644
--- a/examples/armv4t/gdb/memory_map.rs
+++ b/examples/armv4t/gdb/memory_map.rs
@@ -1,17 +1,31 @@
 use gdbstub::target;
+use gdbstub::target::TargetResult;
 
 use crate::emu::Emu;
 
 impl target::ext::memory_map::MemoryMap for Emu {
-    fn memory_map_xml(&self) -> &str {
+    fn memory_map_xml(
+        &self,
+        offset: u64,
+        length: usize,
+        buf: &mut [u8],
+    ) -> TargetResult<usize, Self> {
         // Sample memory map, with RAM coverying the whole
         // memory space.
-        r#"<?xml version="1.0"?>
+        let memory_map = r#"<?xml version="1.0"?>
 <!DOCTYPE memory-map
     PUBLIC "+//IDN gnu.org//DTD GDB Memory Map V1.0//EN"
             "http://sourceware.org/gdb/gdb-memory-map.dtd">
 <memory-map>
     <memory type="ram" start="0x0" length="0x100000000"/>
 </memory-map>"#
+            .trim()
+            .as_bytes();
+
+        let len = memory_map.len();
+        let data = &memory_map[len.min(offset as usize)..len.min(offset as usize + length)];
+        let buf = &mut buf[..data.len()];
+        buf.copy_from_slice(data);
+        Ok(data.len())
     }
 }
diff --git a/examples/armv4t/gdb/target_description_xml_override.rs b/examples/armv4t/gdb/target_description_xml_override.rs
index 24801310..4fc4d139 100644
--- a/examples/armv4t/gdb/target_description_xml_override.rs
+++ b/examples/armv4t/gdb/target_description_xml_override.rs
@@ -1,10 +1,16 @@
 use gdbstub::target;
+use gdbstub::target::TargetResult;
 
 use crate::emu::Emu;
 
 impl target::ext::target_description_xml_override::TargetDescriptionXmlOverride for Emu {
-    fn target_description_xml(&self) -> &str {
-        r#"<?xml version="1.0"?>
+    fn target_description_xml(
+        &self,
+        offset: u64,
+        length: usize,
+        buf: &mut [u8],
+    ) -> TargetResult<usize, Self> {
+        let xml = r#"<?xml version="1.0"?>
 <!DOCTYPE target SYSTEM "gdb-target.dtd">
 <target version="1.0">
     <architecture>armv4t</architecture>
@@ -67,5 +73,13 @@ impl target::ext::target_description_xml_override::TargetDescriptionXmlOverride
     </feature>
 </target>
         "#
+        .trim()
+        .as_bytes();
+
+        let len = xml.len();
+        let data = &xml[len.min(offset as usize)..len.min(offset as usize + length)];
+        let buf = &mut buf[..data.len()];
+        buf.copy_from_slice(data);
+        Ok(data.len())
     }
 }
diff --git a/src/gdbstub_impl/ext/base.rs b/src/gdbstub_impl/ext/base.rs
index cfbfe678..1f5825a7 100644
--- a/src/gdbstub_impl/ext/base.rs
+++ b/src/gdbstub_impl/ext/base.rs
@@ -127,20 +127,29 @@ impl<T: Target, C: Connection> GdbStubImpl<T, C> {
             }
             Base::qXferFeaturesRead(cmd) => {
                 #[allow(clippy::redundant_closure)]
-                let xml = target
-                    .target_description_xml_override()
-                    .map(|ops| ops.target_description_xml())
-                    .or_else(|| T::Arch::target_description_xml());
-
-                match xml {
-                    Some(xml) => {
+                let ret = if let Some(ops) = target.target_description_xml_override() {
+                    ops.target_description_xml(cmd.offset, cmd.length, cmd.buf)
+                        .handle_error()?
+                } else {
+                    if let Some(xml) = T::Arch::target_description_xml() {
                         let xml = xml.trim().as_bytes();
-                        res.write_binary_range(xml, cmd.offset, cmd.len)?;
+                        let len = xml.len();
+                        let data = &xml[len.min(cmd.offset as usize)
+                            ..len.min(cmd.offset as usize + cmd.length)];
+                        let buf = &mut cmd.buf[..data.len()];
+                        buf.copy_from_slice(data);
+                        data.len()
+                    } else {
+                        0
                     }
-                    // If the target hasn't provided their own XML, then the initial response to
-                    // "qSupported" wouldn't have included "qXfer:features:read", and gdb wouldn't
-                    // send this packet unless it was explicitly marked as supported.
-                    None => return Err(Error::PacketUnexpected),
+                };
+
+                if ret == 0 {
+                    res.write_str("l")?;
+                } else {
+                    res.write_str("m")?;
+                    // TODO: add more specific error variant?
+                    res.write_binary(cmd.buf.get(..ret).ok_or(Error::PacketBufferOverflow)?)?;
                 }
                 HandlerStatus::Handled
             }
diff --git a/src/gdbstub_impl/ext/host_io.rs b/src/gdbstub_impl/ext/host_io.rs
index 911decda..f9afa647 100644
--- a/src/gdbstub_impl/ext/host_io.rs
+++ b/src/gdbstub_impl/ext/host_io.rs
@@ -2,7 +2,7 @@ use super::prelude::*;
 use crate::protocol::commands::ext::HostIo;
 
 use crate::arch::Arch;
-use crate::target::ext::host_io::{HostIoError, HostIoOutput, HostIoStat};
+use crate::target::ext::host_io::{HostIoError, HostIoStat};
 
 impl<T: Target, C: Connection> GdbStubImpl<T, C> {
     pub(crate) fn handle_host_io(
@@ -52,31 +52,16 @@ impl<T: Target, C: Connection> GdbStubImpl<T, C> {
                 HandlerStatus::Handled
             }
             HostIo::vFilePread(cmd) if ops.enable_pread().is_some() => {
-                let count = <T::Arch as Arch>::Usize::from_be_bytes(cmd.count)
-                    .ok_or(Error::TargetMismatch)?;
-                let offset = <T::Arch as Arch>::Usize::from_be_bytes(cmd.offset)
-                    .ok_or(Error::TargetMismatch)?;
-                let mut err: Result<_, Error<T::Error, C::Error>> = Ok(());
-                let mut callback = |data: &[u8]| {
-                    let e = (|| {
+                let ops = ops.enable_pread().unwrap();
+                handle_hostio_result! {
+                    if let Ok(ret) = ops.pread(cmd.fd, cmd.count, cmd.offset, cmd.buf) => {
                         res.write_str("F")?;
-                        res.write_num(data.len())?;
+                        res.write_num(ret)?;
                         res.write_str(";")?;
-                        res.write_binary(data)?;
-                        Ok(())
-                    })();
-
-                    if let Err(e) = e {
-                        err = Err(e)
+                        res.write_binary(cmd.buf.get(..ret).ok_or(Error::PacketBufferOverflow)?)?;
                     }
                 };
 
-                let ops = ops.enable_pread().unwrap();
-                handle_hostio_result! {
-                    if let Ok(_) = ops.pread(cmd.fd, count, offset, HostIoOutput::new(&mut callback)) => {}
-                };
-                err?;
-
                 HandlerStatus::Handled
             }
             HostIo::vFilePwrite(cmd) if ops.enable_pwrite().is_some() => {
@@ -126,27 +111,16 @@ impl<T: Target, C: Connection> GdbStubImpl<T, C> {
                 HandlerStatus::Handled
             }
             HostIo::vFileReadlink(cmd) if ops.enable_readlink().is_some() => {
-                let mut err: Result<_, Error<T::Error, C::Error>> = Ok(());
-                let mut callback = |data: &[u8]| {
-                    let e = (|| {
+                let ops = ops.enable_readlink().unwrap();
+                handle_hostio_result! {
+                    if let Ok(ret) = ops.readlink(cmd.filename, cmd.buf) => {
                         res.write_str("F")?;
-                        res.write_num(data.len())?;
+                        res.write_num(ret)?;
                         res.write_str(";")?;
-                        res.write_binary(data)?;
-                        Ok(())
-                    })();
-
-                    if let Err(e) = e {
-                        err = Err(e)
+                        res.write_binary(cmd.buf.get(..ret).ok_or(Error::PacketBufferOverflow)?)?;
                     }
                 };
 
-                let ops = ops.enable_readlink().unwrap();
-                handle_hostio_result! {
-                    if let Ok(_) = ops.readlink(cmd.filename, HostIoOutput::new(&mut callback)) => {}
-                };
-                err?;
-
                 HandlerStatus::Handled
             }
             HostIo::vFileSetfs(cmd) if ops.enable_setfs().is_some() => {
diff --git a/src/gdbstub_impl/ext/memory_map.rs b/src/gdbstub_impl/ext/memory_map.rs
index 7003ca7f..cb622b93 100644
--- a/src/gdbstub_impl/ext/memory_map.rs
+++ b/src/gdbstub_impl/ext/memory_map.rs
@@ -17,8 +17,16 @@ impl<T: Target, C: Connection> GdbStubImpl<T, C> {
 
         let handler_status = match command {
             MemoryMap::qXferMemoryMapRead(cmd) => {
-                let xml = ops.memory_map_xml().trim().as_bytes();
-                res.write_binary_range(xml, cmd.offset, cmd.len)?;
+                let ret = ops
+                    .memory_map_xml(cmd.offset, cmd.length, cmd.buf)
+                    .handle_error()?;
+                if ret == 0 {
+                    res.write_str("l")?;
+                } else {
+                    res.write_str("m")?;
+                    // TODO: add more specific error variant?
+                    res.write_binary(cmd.buf.get(..ret).ok_or(Error::PacketBufferOverflow)?)?;
+                }
                 HandlerStatus::Handled
             }
         };
diff --git a/src/protocol/commands.rs b/src/protocol/commands.rs
index b171ea6e..4500af87 100644
--- a/src/protocol/commands.rs
+++ b/src/protocol/commands.rs
@@ -180,7 +180,7 @@ commands! {
         "QStartNoAckMode" => _QStartNoAckMode::QStartNoAckMode,
         "qsThreadInfo" => _qsThreadInfo::qsThreadInfo,
         "qSupported" => _qSupported::qSupported<'a>,
-        "qXfer:features:read" => _qXfer_features_read::qXferFeaturesRead,
+        "qXfer:features:read" => _qXfer_features_read::qXferFeaturesRead<'a>,
         "s" => _s::s<'a>,
         "T" => _t_upcase::T,
         "vCont" => _vCont::vCont<'a>,
@@ -221,8 +221,8 @@ commands! {
         "bs" => _bs::bs,
     }
 
-    memory_map {
-        "qXfer:memory-map:read" => _qXfer_memory_map::qXferMemoryMapRead,
+    memory_map use 'a {
+        "qXfer:memory-map:read" => _qXfer_memory_map::qXferMemoryMapRead<'a>,
     }
 
     exec_file use 'a {
diff --git a/src/protocol/commands/_qXfer_features_read.rs b/src/protocol/commands/_qXfer_features_read.rs
index 6e6d3777..cc89544e 100644
--- a/src/protocol/commands/_qXfer_features_read.rs
+++ b/src/protocol/commands/_qXfer_features_read.rs
@@ -1,14 +1,17 @@
 use super::prelude::*;
 
 #[derive(Debug)]
-pub struct qXferFeaturesRead {
-    pub offset: usize,
-    pub len: usize,
+pub struct qXferFeaturesRead<'a> {
+    pub offset: u64,
+    pub length: usize,
+
+    pub buf: &'a mut [u8],
 }
 
-impl<'a> ParseCommand<'a> for qXferFeaturesRead {
+impl<'a> ParseCommand<'a> for qXferFeaturesRead<'a> {
     fn from_packet(buf: PacketBuf<'a>) -> Option<Self> {
-        let body = buf.into_body();
+        let (buf, body_range) = buf.into_raw_buf();
+        let body = buf.get_mut(body_range.start..body_range.end)?;
 
         if body.is_empty() {
             return None;
@@ -22,8 +25,10 @@ impl<'a> ParseCommand<'a> for qXferFeaturesRead {
 
         let mut body = body.next()?.split(|b| *b == b',');
         let offset = decode_hex(body.next()?).ok()?;
-        let len = decode_hex(body.next()?).ok()?;
+        let length = decode_hex(body.next()?).ok()?;
+
+        drop(body);
 
-        Some(qXferFeaturesRead { offset, len })
+        Some(qXferFeaturesRead { offset, length, buf })
     }
 }
diff --git a/src/protocol/commands/_qXfer_memory_map.rs b/src/protocol/commands/_qXfer_memory_map.rs
index e522de09..df7ed055 100644
--- a/src/protocol/commands/_qXfer_memory_map.rs
+++ b/src/protocol/commands/_qXfer_memory_map.rs
@@ -1,14 +1,17 @@
 use super::prelude::*;
 
 #[derive(Debug)]
-pub struct qXferMemoryMapRead {
-    pub offset: usize,
-    pub len: usize,
+pub struct qXferMemoryMapRead<'a> {
+    pub offset: u64,
+    pub length: usize,
+
+    pub buf: &'a mut [u8],
 }
 
-impl<'a> ParseCommand<'a> for qXferMemoryMapRead {
+impl<'a> ParseCommand<'a> for qXferMemoryMapRead<'a> {
     fn from_packet(buf: PacketBuf<'a>) -> Option<Self> {
-        let body = buf.into_body();
+        let (buf, body_range) = buf.into_raw_buf();
+        let body = buf.get_mut(body_range.start..body_range.end)?;
 
         if body.is_empty() {
             return None;
@@ -22,8 +25,10 @@ impl<'a> ParseCommand<'a> for qXferMemoryMapRead {
 
         let mut body = body.next()?.split(|b| *b == b',');
         let offset = decode_hex(body.next()?).ok()?;
-        let len = decode_hex(body.next()?).ok()?;
+        let length = decode_hex(body.next()?).ok()?;
+
+        drop(body);
 
-        Some(qXferMemoryMapRead { offset, len })
+        Some(qXferMemoryMapRead { offset, length , buf})
     }
 }
diff --git a/src/protocol/commands/_vFile_pread.rs b/src/protocol/commands/_vFile_pread.rs
index 4b795952..b2318297 100644
--- a/src/protocol/commands/_vFile_pread.rs
+++ b/src/protocol/commands/_vFile_pread.rs
@@ -3,13 +3,17 @@ use super::prelude::*;
 #[derive(Debug)]
 pub struct vFilePread<'a> {
     pub fd: u32,
-    pub count: &'a [u8],
-    pub offset: &'a [u8],
+    pub count: usize,
+    pub offset: u64,
+
+    pub buf: &'a mut [u8],
 }
 
 impl<'a> ParseCommand<'a> for vFilePread<'a> {
     fn from_packet(buf: PacketBuf<'a>) -> Option<Self> {
-        let body = buf.into_body();
+        let (buf, body_range) = buf.into_raw_buf();
+        let body = buf.get_mut(body_range.start..body_range.end)?;
+
         if body.is_empty() {
             return None;
         }
@@ -18,9 +22,12 @@ impl<'a> ParseCommand<'a> for vFilePread<'a> {
             [b':', body @ ..] => {
                 let mut body = body.splitn_mut_no_panic(3, |b| *b == b',');
                 let fd = decode_hex(body.next()?).ok()?;
-                let count = decode_hex_buf(body.next()?).ok()?;
-                let offset = decode_hex_buf(body.next()?).ok()?;
-                Some(vFilePread{fd, count, offset})
+                let count = decode_hex(body.next()?).ok()?;
+                let offset = decode_hex(body.next()?).ok()?;
+
+                drop(body);
+
+                Some(vFilePread{fd, count, offset, buf})
             },
             _ => None,
         }
diff --git a/src/protocol/commands/_vFile_readlink.rs b/src/protocol/commands/_vFile_readlink.rs
index 1223bed5..b56201fd 100644
--- a/src/protocol/commands/_vFile_readlink.rs
+++ b/src/protocol/commands/_vFile_readlink.rs
@@ -3,11 +3,15 @@ use super::prelude::*;
 #[derive(Debug)]
 pub struct vFileReadlink<'a> {
     pub filename: &'a [u8],
+
+    pub buf: &'a mut [u8],
 }
 
 impl<'a> ParseCommand<'a> for vFileReadlink<'a> {
     fn from_packet(buf: PacketBuf<'a>) -> Option<Self> {
-        let body = buf.into_body();
+        let (buf, body_range) = buf.into_raw_buf();
+        let (body, buf) = buf[body_range.start..].split_at_mut(body_range.end - body_range.start);
+
         if body.is_empty() {
             return None;
         }
@@ -15,7 +19,7 @@ impl<'a> ParseCommand<'a> for vFileReadlink<'a> {
         match body {
             [b':', body @ ..] => {
                 let filename = decode_hex_buf(body).ok()?;
-                Some(vFileReadlink{filename})
+                Some(vFileReadlink{filename, buf})
             },
             _ => None,
         }
diff --git a/src/protocol/response_writer.rs b/src/protocol/response_writer.rs
index 64c26d28..13c1a97d 100644
--- a/src/protocol/response_writer.rs
+++ b/src/protocol/response_writer.rs
@@ -193,25 +193,6 @@ impl<'a, C: Connection + 'a> ResponseWriter<'a, C> {
         Ok(())
     }
 
-    /// Write a range of data specified by offset and len.
-    /// Used by qXfer:_object_:read commands.
-    pub fn write_binary_range(
-        &mut self,
-        data: &[u8],
-        offset: usize,
-        len: usize,
-    ) -> Result<(), Error<C::Error>> {
-        if offset < data.len() {
-            // still more data
-            self.write_str("m")?;
-            self.write_binary(&data[offset..][..len.min(data.len() - offset)])?
-        } else {
-            // no more data
-            self.write_str("l")?;
-        }
-        Ok(())
-    }
-
     /// Write a number as a big-endian hex string using the most compact
     /// representation possible (i.e: trimming leading zeros).
     pub fn write_num<D: BeBytes + PrimInt>(&mut self, digit: D) -> Result<(), Error<C::Error>> {
diff --git a/src/target/ext/host_io.rs b/src/target/ext/host_io.rs
index 36a60ee3..52898838 100644
--- a/src/target/ext/host_io.rs
+++ b/src/target/ext/host_io.rs
@@ -199,30 +199,6 @@ impl<E> From<std::io::Error> for HostIoError<E> {
 /// See [`HostIoError`] for more details.
 pub type HostIoResult<T, Tgt> = Result<T, HostIoError<<Tgt as Target>::Error>>;
 
-/// Zero-sized type token that ensures HostIoOutput::write is called.
-pub struct HostIoToken<'a>(core::marker::PhantomData<&'a *mut ()>);
-
-/// An interface to send pread data back to the GDB client.
-pub struct HostIoOutput<'a> {
-    cb: &'a mut dyn FnMut(&[u8]),
-    token: HostIoToken<'a>,
-}
-
-impl<'a> HostIoOutput<'a> {
-    pub(crate) fn new(cb: &'a mut dyn FnMut(&[u8])) -> Self {
-        Self {
-            cb,
-            token: HostIoToken(core::marker::PhantomData),
-        }
-    }
-
-    /// Write out raw file bytes to the GDB debugger.
-    pub fn write(self, buf: &[u8]) -> HostIoToken<'a> {
-        (self.cb)(buf);
-        self.token
-    }
-}
-
 /// Target Extension - Perform I/O operations on host
 pub trait HostIo: Target {
     /// Enable open operation.
@@ -309,10 +285,10 @@ pub trait HostIoPread: HostIo {
     fn pread<'a>(
         &mut self,
         fd: u32,
-        count: <Self::Arch as Arch>::Usize,
-        offset: <Self::Arch as Arch>::Usize,
-        output: HostIoOutput<'a>,
-    ) -> HostIoResult<HostIoToken<'a>, Self>;
+        count: usize,
+        offset: u64,
+        buf: &mut [u8],
+    ) -> HostIoResult<usize, Self>;
 }
 
 define_ext!(HostIoPreadOps, HostIoPread);
@@ -362,11 +338,7 @@ pub trait HostIoReadlink: HostIo {
     /// will consume the `output` object and return a [`HostIoToken`]. This
     /// token ensures that the implementer of this method calls
     /// [`HostIoOutput::write`].
-    fn readlink<'a>(
-        &mut self,
-        filename: &[u8],
-        output: HostIoOutput<'a>,
-    ) -> HostIoResult<HostIoToken<'a>, Self>;
+    fn readlink<'a>(&mut self, filename: &[u8], buf: &mut [u8]) -> HostIoResult<usize, Self>;
 }
 
 define_ext!(HostIoReadlinkOps, HostIoReadlink);
diff --git a/src/target/ext/memory_map.rs b/src/target/ext/memory_map.rs
index 59952f39..79e9a557 100644
--- a/src/target/ext/memory_map.rs
+++ b/src/target/ext/memory_map.rs
@@ -1,5 +1,5 @@
 //! Provide a memory map for the target.
-use crate::target::Target;
+use crate::target::{Target, TargetResult};
 
 /// Target Extension - Provide a target memory map.
 pub trait MemoryMap: Target {
@@ -8,7 +8,12 @@ pub trait MemoryMap: Target {
     /// See the [GDB Documentation] for a description of the format.
     ///
     /// [GDB Documentation]: https://sourceware.org/gdb/onlinedocs/gdb/Memory-Map-Format.html
-    fn memory_map_xml(&self) -> &str;
+    fn memory_map_xml(
+        &self,
+        offset: u64,
+        length: usize,
+        buf: &mut [u8],
+    ) -> TargetResult<usize, Self>;
 }
 
 define_ext!(MemoryMapOps, MemoryMap);
diff --git a/src/target/ext/target_description_xml_override.rs b/src/target/ext/target_description_xml_override.rs
index 7cac0340..06068e22 100644
--- a/src/target/ext/target_description_xml_override.rs
+++ b/src/target/ext/target_description_xml_override.rs
@@ -1,5 +1,5 @@
 //! Override the target description XML specified by `Target::Arch`.
-use crate::target::Target;
+use crate::target::{Target, TargetResult};
 
 /// Target Extension - Override the target description XML specified by
 /// `Target::Arch`.
@@ -13,7 +13,12 @@ pub trait TargetDescriptionXmlOverride: Target {
     /// Refer to the
     /// [target_description_xml](crate::arch::Arch::target_description_xml)
     /// docs for more info.
-    fn target_description_xml(&self) -> &str;
+    fn target_description_xml(
+        &self,
+        offset: u64,
+        length: usize,
+        buf: &mut [u8],
+    ) -> TargetResult<usize, Self>;
 }
 
 define_ext!(

From e12debb6acb920e211fa5de0f2acb82ab83e5a7d Mon Sep 17 00:00:00 2001
From: Bet4 <0xbet4@gmail.com>
Date: Sat, 18 Sep 2021 11:25:57 +0800
Subject: [PATCH 2/7] Some fixes

---
 src/gdbstub_impl/ext/base.rs             | 25 ++++++++++++------------
 src/protocol/commands/_vFile_readlink.rs |  1 +
 src/target/ext/host_io.rs                | 18 ++++++++---------
 3 files changed, 22 insertions(+), 22 deletions(-)

diff --git a/src/gdbstub_impl/ext/base.rs b/src/gdbstub_impl/ext/base.rs
index 1f5825a7..dbda7fbd 100644
--- a/src/gdbstub_impl/ext/base.rs
+++ b/src/gdbstub_impl/ext/base.rs
@@ -126,22 +126,23 @@ impl<T: Target, C: Connection> GdbStubImpl<T, C> {
                 HandlerStatus::NeedsOk
             }
             Base::qXferFeaturesRead(cmd) => {
-                #[allow(clippy::redundant_closure)]
                 let ret = if let Some(ops) = target.target_description_xml_override() {
                     ops.target_description_xml(cmd.offset, cmd.length, cmd.buf)
                         .handle_error()?
+                } else if let Some(xml) = T::Arch::target_description_xml() {
+                    let xml = xml.trim().as_bytes();
+                    let len = xml.len();
+                    let data = &xml
+                        [len.min(cmd.offset as usize)..len.min(cmd.offset as usize + cmd.length)];
+                    let buf = &mut cmd.buf[..data.len()];
+                    buf.copy_from_slice(data);
+                    data.len()
                 } else {
-                    if let Some(xml) = T::Arch::target_description_xml() {
-                        let xml = xml.trim().as_bytes();
-                        let len = xml.len();
-                        let data = &xml[len.min(cmd.offset as usize)
-                            ..len.min(cmd.offset as usize + cmd.length)];
-                        let buf = &mut cmd.buf[..data.len()];
-                        buf.copy_from_slice(data);
-                        data.len()
-                    } else {
-                        0
-                    }
+                    // If the target hasn't provided their own XML, then the initial response to
+                    // "qSupported" wouldn't have included "qXfer:features:read", and gdb
+                    // wouldn't send this packet unless it was
+                    // explicitly marked as supported.
+                    return Err(Error::PacketUnexpected);
                 };
 
                 if ret == 0 {
diff --git a/src/protocol/commands/_vFile_readlink.rs b/src/protocol/commands/_vFile_readlink.rs
index b56201fd..8cc2ef81 100644
--- a/src/protocol/commands/_vFile_readlink.rs
+++ b/src/protocol/commands/_vFile_readlink.rs
@@ -10,6 +10,7 @@ pub struct vFileReadlink<'a> {
 impl<'a> ParseCommand<'a> for vFileReadlink<'a> {
     fn from_packet(buf: PacketBuf<'a>) -> Option<Self> {
         let (buf, body_range) = buf.into_raw_buf();
+        // TODO: rewrite to avoid panic
         let (body, buf) = buf[body_range.start..].split_at_mut(body_range.end - body_range.start);
 
         if body.is_empty() {
diff --git a/src/target/ext/host_io.rs b/src/target/ext/host_io.rs
index 52898838..e105e37f 100644
--- a/src/target/ext/host_io.rs
+++ b/src/target/ext/host_io.rs
@@ -278,11 +278,12 @@ pub trait HostIoPread: HostIo {
     /// Up to `count` bytes will be read from the file, starting at `offset`
     /// relative to the start of the file.
     ///
-    /// The data read _must_ be sent by calling [`HostIoOutput::write`], which
-    /// will consume the `output` object and return a [`HostIoToken`]. This
-    /// token ensures that the implementer of this method calls
-    /// [`HostIoOutput::write`].
-    fn pread<'a>(
+    /// Return the number of bytes written into `buf` (which may be less than
+    /// `count`).
+    ///
+    /// If `offset` is greater than the length of the underlying data, return
+    /// `Ok(0)`.
+    fn pread(
         &mut self,
         fd: u32,
         count: usize,
@@ -334,11 +335,8 @@ define_ext!(HostIoUnlinkOps, HostIoUnlink);
 pub trait HostIoReadlink: HostIo {
     /// Read value of symbolic link `filename` on the target.
     ///
-    /// The data read _must_ be sent by calling [`HostIoOutput::write`], which
-    /// will consume the `output` object and return a [`HostIoToken`]. This
-    /// token ensures that the implementer of this method calls
-    /// [`HostIoOutput::write`].
-    fn readlink<'a>(&mut self, filename: &[u8], buf: &mut [u8]) -> HostIoResult<usize, Self>;
+    /// Return the number of bytes written into `buf`.
+    fn readlink(&mut self, filename: &[u8], buf: &mut [u8]) -> HostIoResult<usize, Self>;
 }
 
 define_ext!(HostIoReadlinkOps, HostIoReadlink);

From b9800bb8563a474e11c13c1e22599140cb64f3a4 Mon Sep 17 00:00:00 2001
From: Bet4 <0xbet4@gmail.com>
Date: Sat, 18 Sep 2021 15:17:23 +0800
Subject: [PATCH 3/7] Add helper function to copy range of data to buf

---
 examples/armv4t/gdb/exec_file.rs              |  7 ++-----
 examples/armv4t/gdb/host_io.rs                | 21 +++++--------------
 examples/armv4t/gdb/memory_map.rs             |  8 ++-----
 examples/armv4t/gdb/mod.rs                    |  8 +++++++
 .../gdb/target_description_xml_override.rs    |  7 ++-----
 5 files changed, 19 insertions(+), 32 deletions(-)

diff --git a/examples/armv4t/gdb/exec_file.rs b/examples/armv4t/gdb/exec_file.rs
index c130a9dc..e70a022a 100644
--- a/examples/armv4t/gdb/exec_file.rs
+++ b/examples/armv4t/gdb/exec_file.rs
@@ -2,6 +2,7 @@ use gdbstub::common::Pid;
 use gdbstub::target;
 use gdbstub::target::TargetResult;
 
+use super::copy_range_to_buf;
 use crate::emu::Emu;
 
 impl target::ext::exec_file::ExecFile for Emu {
@@ -13,10 +14,6 @@ impl target::ext::exec_file::ExecFile for Emu {
         buf: &mut [u8],
     ) -> TargetResult<usize, Self> {
         let filename = b"/test.elf";
-        let len = filename.len();
-        let data = &filename[len.min(offset as usize)..len.min(offset as usize + length)];
-        let buf = &mut buf[..data.len()];
-        buf.copy_from_slice(data);
-        Ok(data.len())
+        Ok(copy_range_to_buf(filename, offset, length, buf))
     }
 }
diff --git a/examples/armv4t/gdb/host_io.rs b/examples/armv4t/gdb/host_io.rs
index 74f2703a..81bd5ff5 100644
--- a/examples/armv4t/gdb/host_io.rs
+++ b/examples/armv4t/gdb/host_io.rs
@@ -5,6 +5,7 @@ use gdbstub::target::ext::host_io::{
     FsKind, HostIoErrno, HostIoError, HostIoOpenFlags, HostIoOpenMode, HostIoResult, HostIoStat,
 };
 
+use super::copy_range_to_buf;
 use crate::emu::Emu;
 use crate::TEST_PROGRAM_ELF;
 
@@ -138,12 +139,7 @@ impl target::ext::host_io::HostIoPread for Emu {
     ) -> HostIoResult<usize, Self> {
         if fd < FD_RESERVED {
             if fd == 0 {
-                let len = TEST_PROGRAM_ELF.len();
-                let data =
-                    &TEST_PROGRAM_ELF[len.min(offset as usize)..len.min(offset as usize + count)];
-                let buf = &mut buf[..data.len()];
-                buf.copy_from_slice(data);
-                return Ok(data.len());
+                return Ok(copy_range_to_buf(TEST_PROGRAM_ELF, offset, count, buf));
             } else {
                 return Err(HostIoError::Errno(HostIoErrno::EBADF));
             }
@@ -250,15 +246,11 @@ impl target::ext::host_io::HostIoReadlink for Emu {
         if filename == b"/proc/1/exe" {
             // Support `info proc exe` command
             let exe = b"/test.elf";
-            let buf = &mut buf[..exe.len()];
-            buf.copy_from_slice(exe);
-            return Ok(exe.len());
+            return Ok(copy_range_to_buf(exe, 0, exe.len(), buf));
         } else if filename == b"/proc/1/cwd" {
             // Support `info proc cwd` command
             let cwd = b"/";
-            let buf = &mut buf[..cwd.len()];
-            buf.copy_from_slice(cwd);
-            return Ok(cwd.len());
+            return Ok(copy_range_to_buf(cwd, 0, cwd.len(), buf));
         } else if filename.starts_with(b"/proc") {
             return Err(HostIoError::Errno(HostIoErrno::ENOENT));
         }
@@ -270,10 +262,7 @@ impl target::ext::host_io::HostIoReadlink for Emu {
             .to_str()
             .ok_or(HostIoError::Errno(HostIoErrno::ENOENT))?
             .as_bytes();
-        let len = data.len();
-        let buf = &mut buf[..len];
-        buf.copy_from_slice(data);
-        Ok(len)
+        Ok(copy_range_to_buf(data, 0, data.len(), buf))
     }
 }
 
diff --git a/examples/armv4t/gdb/memory_map.rs b/examples/armv4t/gdb/memory_map.rs
index 82d26a1d..ddddb654 100644
--- a/examples/armv4t/gdb/memory_map.rs
+++ b/examples/armv4t/gdb/memory_map.rs
@@ -1,6 +1,7 @@
 use gdbstub::target;
 use gdbstub::target::TargetResult;
 
+use super::copy_range_to_buf;
 use crate::emu::Emu;
 
 impl target::ext::memory_map::MemoryMap for Emu {
@@ -21,11 +22,6 @@ impl target::ext::memory_map::MemoryMap for Emu {
 </memory-map>"#
             .trim()
             .as_bytes();
-
-        let len = memory_map.len();
-        let data = &memory_map[len.min(offset as usize)..len.min(offset as usize + length)];
-        let buf = &mut buf[..data.len()];
-        buf.copy_from_slice(data);
-        Ok(data.len())
+        Ok(copy_range_to_buf(memory_map, offset, length, buf))
     }
 }
diff --git a/examples/armv4t/gdb/mod.rs b/examples/armv4t/gdb/mod.rs
index 89929cc1..3167b9fd 100644
--- a/examples/armv4t/gdb/mod.rs
+++ b/examples/armv4t/gdb/mod.rs
@@ -36,6 +36,14 @@ fn cpu_reg_id(id: ArmCoreRegId) -> Option<u8> {
     }
 }
 
+pub fn copy_range_to_buf(data: &[u8], offset: u64, length: usize, buf: &mut [u8]) -> usize {
+    let len = data.len();
+    let data = &data[len.min(offset as usize)..len.min(offset as usize + length)];
+    let buf = &mut buf[..data.len()];
+    buf.copy_from_slice(data);
+    data.len()
+}
+
 impl Target for Emu {
     // As an example, I've defined a custom architecture based off
     // `gdbstub_arch::arm::Armv4t`. The implementation is in the `custom_arch`
diff --git a/examples/armv4t/gdb/target_description_xml_override.rs b/examples/armv4t/gdb/target_description_xml_override.rs
index 4fc4d139..714c0716 100644
--- a/examples/armv4t/gdb/target_description_xml_override.rs
+++ b/examples/armv4t/gdb/target_description_xml_override.rs
@@ -1,6 +1,7 @@
 use gdbstub::target;
 use gdbstub::target::TargetResult;
 
+use super::copy_range_to_buf;
 use crate::emu::Emu;
 
 impl target::ext::target_description_xml_override::TargetDescriptionXmlOverride for Emu {
@@ -76,10 +77,6 @@ impl target::ext::target_description_xml_override::TargetDescriptionXmlOverride
         .trim()
         .as_bytes();
 
-        let len = xml.len();
-        let data = &xml[len.min(offset as usize)..len.min(offset as usize + length)];
-        let buf = &mut buf[..data.len()];
-        buf.copy_from_slice(data);
-        Ok(data.len())
+        Ok(copy_range_to_buf(xml, offset, length, buf))
     }
 }

From 35b8db4578520a4f96e228730649b63fe719d9d8 Mon Sep 17 00:00:00 2001
From: Bet4 <0xbet4@gmail.com>
Date: Sun, 19 Sep 2021 10:56:02 +0800
Subject: [PATCH 4/7] Elide slice indexing bounds checks

---
 examples/armv4t/gdb/mod.rs   |  4 ++++
 src/gdbstub_impl/ext/base.rs | 24 +++++++++++++++---------
 2 files changed, 19 insertions(+), 9 deletions(-)

diff --git a/examples/armv4t/gdb/mod.rs b/examples/armv4t/gdb/mod.rs
index 3167b9fd..7f03cab1 100644
--- a/examples/armv4t/gdb/mod.rs
+++ b/examples/armv4t/gdb/mod.rs
@@ -36,6 +36,10 @@ fn cpu_reg_id(id: ArmCoreRegId) -> Option<u8> {
     }
 }
 
+/// Copy a range of `data` (start at `offset` with a size of `length`) to `buf`.
+/// Return the size of data copied. Return 0 if encounter EOF.
+///
+/// Mainly used by qXfer:_object_:read commands.
 pub fn copy_range_to_buf(data: &[u8], offset: u64, length: usize, buf: &mut [u8]) -> usize {
     let len = data.len();
     let data = &data[len.min(offset as usize)..len.min(offset as usize + length)];
diff --git a/src/gdbstub_impl/ext/base.rs b/src/gdbstub_impl/ext/base.rs
index dbda7fbd..561cd106 100644
--- a/src/gdbstub_impl/ext/base.rs
+++ b/src/gdbstub_impl/ext/base.rs
@@ -131,17 +131,23 @@ impl<T: Target, C: Connection> GdbStubImpl<T, C> {
                         .handle_error()?
                 } else if let Some(xml) = T::Arch::target_description_xml() {
                     let xml = xml.trim().as_bytes();
-                    let len = xml.len();
-                    let data = &xml
-                        [len.min(cmd.offset as usize)..len.min(cmd.offset as usize + cmd.length)];
-                    let buf = &mut cmd.buf[..data.len()];
-                    buf.copy_from_slice(data);
-                    data.len()
+                    let xml_len = xml.len();
+
+                    let start = xml_len.min(cmd.offset as usize);
+                    let end = xml_len.min(cmd.offset as usize + cmd.length);
+
+                    // LLVM isn't smart enough to realize that `end` will always be greater than
+                    // `start`, and fails to elide the `slice_index_order_fail` check unless we
+                    // include this seemingly useless call to `max`.
+                    let data = &xml[start..end.max(start)];
+
+                    let n = data.len().min(cmd.buf.len());
+                    cmd.buf[..n].copy_from_slice(&data[..n]);
+                    n
                 } else {
                     // If the target hasn't provided their own XML, then the initial response to
-                    // "qSupported" wouldn't have included "qXfer:features:read", and gdb
-                    // wouldn't send this packet unless it was
-                    // explicitly marked as supported.
+                    // "qSupported" wouldn't have included "qXfer:features:read", and gdb wouldn't
+                    // send this packet unless it was explicitly marked as supported.
                     return Err(Error::PacketUnexpected);
                 };
 

From 8e640c4ad5cb5febb0026f17aaf03c13773c8f47 Mon Sep 17 00:00:00 2001
From: Bet4 <0xbet4@gmail.com>
Date: Mon, 20 Sep 2021 10:24:40 +0800
Subject: [PATCH 5/7] Update src/target/ext/host_io.rs

Co-authored-by: Daniel Prilik <danielprilik@gmail.com>
---
 src/target/ext/host_io.rs | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/target/ext/host_io.rs b/src/target/ext/host_io.rs
index e105e37f..9161ff8f 100644
--- a/src/target/ext/host_io.rs
+++ b/src/target/ext/host_io.rs
@@ -336,6 +336,10 @@ pub trait HostIoReadlink: HostIo {
     /// Read value of symbolic link `filename` on the target.
     ///
     /// Return the number of bytes written into `buf`.
+    ///
+    /// Unlike most other Host IO handlers, if the resolved file path exceeds
+    /// the length of the provided `buf`, the target should NOT return a
+    /// partial response, and MUST return a `Err(HostIoErrno::ENAMETOOLONG)`.
     fn readlink(&mut self, filename: &[u8], buf: &mut [u8]) -> HostIoResult<usize, Self>;
 }
 

From 532c33328407c0412f974e9f6c5f405e16914383 Mon Sep 17 00:00:00 2001
From: Bet4 <0xbet4@gmail.com>
Date: Tue, 21 Sep 2021 09:34:10 +0800
Subject: [PATCH 6/7] Add more checks on copy_range_to_buf

---
 examples/armv4t/gdb/host_io.rs |  6 +++++-
 examples/armv4t/gdb/mod.rs     | 10 +++++++---
 2 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/examples/armv4t/gdb/host_io.rs b/examples/armv4t/gdb/host_io.rs
index 81bd5ff5..80a9771f 100644
--- a/examples/armv4t/gdb/host_io.rs
+++ b/examples/armv4t/gdb/host_io.rs
@@ -262,7 +262,11 @@ impl target::ext::host_io::HostIoReadlink for Emu {
             .to_str()
             .ok_or(HostIoError::Errno(HostIoErrno::ENOENT))?
             .as_bytes();
-        Ok(copy_range_to_buf(data, 0, data.len(), buf))
+        if data.len() <= buf.len() {
+            Ok(copy_range_to_buf(data, 0, data.len(), buf))
+        } else {
+            Err(HostIoError::Errno(HostIoErrno::ENAMETOOLONG))
+        }
     }
 }
 
diff --git a/examples/armv4t/gdb/mod.rs b/examples/armv4t/gdb/mod.rs
index 7f03cab1..3eb22095 100644
--- a/examples/armv4t/gdb/mod.rs
+++ b/examples/armv4t/gdb/mod.rs
@@ -1,4 +1,4 @@
-use core::convert::TryInto;
+use core::convert::{TryFrom, TryInto};
 
 use armv4t_emu::{reg, Memory};
 use gdbstub::target;
@@ -37,12 +37,16 @@ fn cpu_reg_id(id: ArmCoreRegId) -> Option<u8> {
 }
 
 /// Copy a range of `data` (start at `offset` with a size of `length`) to `buf`.
-/// Return the size of data copied. Return 0 if encounter EOF.
+/// Return the size of data copied. Returns 0 if `offset >= buf.len()`.
 ///
 /// Mainly used by qXfer:_object_:read commands.
 pub fn copy_range_to_buf(data: &[u8], offset: u64, length: usize, buf: &mut [u8]) -> usize {
+    let offset = match usize::try_from(offset) {
+        Ok(v) => v,
+        Err(_) => return 0,
+    };
     let len = data.len();
-    let data = &data[len.min(offset as usize)..len.min(offset as usize + length)];
+    let data = &data[len.min(offset)..len.min(offset + length)];
     let buf = &mut buf[..data.len()];
     buf.copy_from_slice(data);
     data.len()

From b3e31e1a6db04ba7f1bf2aa70075970952433843 Mon Sep 17 00:00:00 2001
From: Bet4 <0xbet4@gmail.com>
Date: Wed, 22 Sep 2021 08:38:03 +0800
Subject: [PATCH 7/7] Final fix

---
 examples/armv4t/gdb/target_description_xml_override.rs | 1 -
 1 file changed, 1 deletion(-)

diff --git a/examples/armv4t/gdb/target_description_xml_override.rs b/examples/armv4t/gdb/target_description_xml_override.rs
index 714c0716..a0c7563b 100644
--- a/examples/armv4t/gdb/target_description_xml_override.rs
+++ b/examples/armv4t/gdb/target_description_xml_override.rs
@@ -76,7 +76,6 @@ impl target::ext::target_description_xml_override::TargetDescriptionXmlOverride
         "#
         .trim()
         .as_bytes();
-
         Ok(copy_range_to_buf(xml, offset, length, buf))
     }
 }