int.str() causes Unhandled page fault when built with -shared on Windows

[syobocat]

Describe the bug

Calling int.str() causes Unhandled page fault on Windows, when the code is built with -shared

Reproduction Steps

I have created a repository for demonstration, and prepared sample binaries built on GitHub Actions.

code.v:

@[export: 'func']
fn func() {
	println('Begin DLL')
	for i in 0 .. 10 {
		println('${i}')
	}
	println('End DLL')
}

loader.c:

#include <stdio.h>
#include <windows.h>

typedef void(*FUNC)();

int main(void) {
	HMODULE hModule = LoadLibraryW(L"code.dll");
	if (hModule == NULL) {
		DWORD e = GetLastError();
		printf("Failed: %d\r\n", e);
		return 1;
	}
	FUNC func = (FUNC)GetProcAddress(hModule, "func");
	printf("Begin\r\n");
	func();
	printf("End\r\n");
	return 0;
}

Expected Behavior

The following should be printed:

Begin
Begin DLL
0
1
2
3
4
5
6
7
8
9
End DLL
End

Current Behavior

On Windows:

Begin
Begin DLL
0

On Wine:

Begin
Begin DLL
0
wine: Unhandled page fault on read access to 0000000000000002 at address 000000001001CCFE (thread 0024), starting debugger...

Possible Solution

No response

Additional Information/Context

No response

V version

V 0.4.9 d5aa37d

Environment details (OS name and version, etc.)

GitHub Actions:

V full version	V 0.4.9 d5aa37d
OS	windows, Microsoft Windows Server 2022 Datacenter 20348 64-bit
Processor	4 cpus, 64bit, little endian, AMD EPYC 7763 64-Core Processor
Memory	13.57GB/16GB
V executable	C:\hostedtoolcache\windows\v\0.4.9\x64\v.exe
V last modified time	2025-01-17 10:34:01
V home dir	OK, value: C:\hostedtoolcache\windows\v\0.4.9\x64
VMODULES	OK, value: C:\Users\runneradmin.vmodules
VTMP	OK, value: C:\Users\runneradmin\AppData\Local\Temp\v_0
Current working dir	OK, value: D:\a\demo\demo
Git version	git version 2.47.1.windows.1
V git status	Error: fatal: not a git repository (or any of the parent directories): .git
.git/config present	false
cc version	N/A
gcc version	gcc (x86_64-posix-seh-rev2, Built by MinGW-W64 project) 12.2.0
clang version	clang version 18.1.8
msvc version	N/A
tcc version	tcc version 0.9.27 (x86_64 Windows)
tcc git status	thirdparty-windows-amd64 b425ac82
emcc version	N/A
glibc version	ldd (cygwin) 3.5.4

Also tested on a real machine:

V full version	V 0.4.9 d5aa37d
OS	windows,
Processor	4 cpus, 64bit, little endian, N/A
Memory	4.01GB/7.89GB
V executable	C:\Users\syobon\v\v.exe
V last modified time	2025-01-17 09:51:49
V home dir	OK, value: C:\Users\syobon\v
VMODULES	OK, value: C:\Users\syobon.vmodules
VTMP	OK, value: C:\Users\syobon\AppData\Local\Temp\v_0
Current working dir	OK, value: C:\Users\syobon\Desktop
Git version	git version 2.47.1.windows.2
V git status	weekly.2025.1-69-gd5aa37d8
.git/config present	true
cc version	N/A
gcc version	N/A
clang version	N/A
msvc version	N/A
tcc version	tcc version 0.9.27 (x86_64 Windows)
tcc git status	thirdparty-windows-amd64 b425ac82
emcc version	N/A
glibc version	N/A

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[huly-for-github]

Connected to Huly®: V_0.6-21925

[kbkpbot]

This is because V's dll need to call _vinit_caller before any other call, and call _vcleanup_caller before you release the dll.

A modified version of your code:

#include <stdio.h>
#include <windows.h>

typedef void(*FUNC)();

typedef void (*fn_vinit_caller)();
typedef void (*fn_vcleanup_caller)();

int main(void) {
	HMODULE hModule = LoadLibraryW(L"code.dll");
	if (hModule == NULL) {
		DWORD e = GetLastError();
		printf("Failed: %d\r\n", e);
		return 1;
	}
	fn_vinit_caller _vinit_caller = (fn_vinit_caller)GetProcAddress(hModule, "_vinit_caller");
	fn_vcleanup_caller _vcleanup_caller = (fn_vcleanup_caller)GetProcAddress(hModule, "_vcleanup_caller");
	_vinit_caller(); // call this before any other call
	FUNC func = (FUNC)GetProcAddress(hModule, "func");
	printf("Begin\r\n");
	func();
	printf("End\r\n");
	_vcleanup_caller(); // call this before you release the dll
	return 0;
}

[kbkpbot]

Or we need to create a V version of LoadLibrary and FreeLibrary?

Oh, we already have dl.open....

[syobocat]

This is because V's dll need to call _vinit_caller before any other call, and call _vcleanup_caller before you release the dll.

I want to load my DLL from an external program, how can I handle that?

[spytheman]

I want to load my DLL from an external program, how can I handle that?

See the modified example, that @kbkpbot posted.
It shows what to do.

[syobocat]

It shows what to do.

The "external program" I want to use is proprietary and I have no access to the source, so is there any way to call _vinit_caller and _vcleanup_caller from DLL side?

[kbkpbot]

It shows what to do.

The "external program" I want to use is proprietary and I have no access to the source, so is there any way to call _vinit_caller and _vcleanup_caller from DLL side?

1. You can make a LoadLibrary hook, in which you can LoadLibrary first and then call the _vinit_caller, or
2. I will make a PR which will let your v function can call the _vinit_caller.

[kbkpbot]

After apply the PR #23507, you can modify your DLL code as follow:

fn C._vinit_caller()
fn C._vcleanup_caller()

@[export: 'func']
fn func() {
	C._vinit_caller()          // must call first
	println('Begin DLL')
	for i in 0 .. 10 {
		println('${i}')
	}
	println('End DLL')
	C._vcleanup_caller()    // must call last,  note, currently , it is an empty function....
}

Every your export function, should call _vinit_caller()/_vcleanup_caller()...
This is a workaround.

[jorgeluismireles]

Question. Is possible to make a specific module where to put _vinit_caller and _vcleanup_caller like this:

module dll // xxx.xxx.dll

fn C._vinit_caller()
fn C._vcleanup_caller()

fn init() {
    C._vinint_caller()
}

fn cleanup() {
    C._vcleanup_caller()
}

And then use the above by importing xxx.xxx.xxx.dll as _ ?

import xxx.xxx.dll as _

@[export: 'func']
fn func() {
	println('Begin DLL')
	for i in 0 .. 10 {
		println('${i}')
	}
	println('End DLL')
}