Compilation fails with -mips16 flag

[andreaskse]

Summary

When compiling with mips16 the assembler in bn_muil.h https://github.com/Mbed-TLS/mbedtls/blob/main/library/bn_mul.h
fails with error messsage:
[12%] Building C object library/CMakeFiles/mbedcrypto.dir/bignum_core.c.o cd /workspace/2UGW/ugw_sw/openwrt/build_dir/xRX500_BootCore/build_dir/target-mips_24kc_musl/mbedtls-3.6.2/library && /workspace/2UGW/ugw_sw/openwrt/build_dir/xRX500_BootCore/staging_dir/toolchain-mips_24kc_gcc-8.3.0_musl/bin/mips-openwrt-linux-musl-gcc -Dmbedcrypto_EXPORTS -I/workspace/2UGW/ugw_sw/openwrt/build_dir/xRX500_BootCore/build_dir/target-mips_24kc_musl/mbedtls-3.6.2/include -I/workspace/2UGW/ugw_sw/openwrt/build_dir/xRX500_BootCore/build_dir/target-mips_24kc_musl/mbedtls-3.6.2/library -I/workspace/2UGW/ugw_sw/openwrt/build_dir/xRX500_BootCore/build_dir/target-mips_24kc_musl/mbedtls-3.6.2/3rdparty/everest/include -I/workspace/2UGW/ugw_sw/openwrt/build_dir/xRX500_BootCore/build_dir/target-mips_24kc_musl/mbedtls-3.6.2/3rdparty/p256-m -I/workspace/2UGW/ugw_sw/openwrt/build_dir/xRX500_BootCore/build_dir/target-mips_24kc_musl/mbedtls-3.6.2/3rdparty/p256-m/p256-m -pipe -mno-branch-likely -mips32r2 -mtune=24kc -g -fno-caller-saves -fno-plt -fhonour-copts -Wno-error=unused-but-set-variable -Wno-error=unused-result - msoft-float -mips16 -minterlink-mips16 -fmacro-prefix-map=/workspace/2UGW/ugw_sw/openwrt/build_dir/xRX500_BootCore/build_dir/target-mips_24kc_musl/mbedtls-3.6.2=mbedtls-3.6.2 -Wformat -Werror=format-security -fpic -fstack-protector-strong -D_FORTIFY_SOURCE=2 -Wl,-z,now -Wl,-z,relro -Wall -Wextra -Wwrite-strings -Wmissing-prototypes -Wformat=2 -Wno-format-nonliteral -Wvla -Wlogical-op -Wshadow -Wformat-signedness -Wformat-overflow=2 -Wformat-truncation -Werror -Wmissing-declarations -O2 -fPIC -std=c99 -o CMakeFiles/mbedcrypto.dir/bignum_core.c.o -c /workspace/2UGW/ugw_sw/openwrt/build_dir/xRX500_BootCore/build_dir/target-mips_24kc_musl/mbedtls-3.6.2/library/bignum_core.c {standard input}: Assembler messages: {standard input}:2982: Error: invalid operands lw $10,24($sp)'
{standard input}:2983: Error: invalid operands lw $11,28($sp)' {standard input}:2984: Error: invalid operands lw $12,32($sp)'
{standard input}:2985: Error: invalid operands lw $13,64($sp)' {standard input}:2986: Error: invalid operands lw $14,0($10)'
{standard input}:2987: Error: invalid operands multu $13,$14' {standard input}:2988: Error: unrecognized opcode addi $10,$10,4'
{standard input}:2989: Error: invalid operands mflo $14' ...

System information

Mbed TLS version (number or commit id): 3.6.2
Operating system and version: Ubuntu
Configuration (if not default, please attach mbedtls_config.h): default
Compiler and options (if you used a pre-built binary, please indicate how you obtained it):
Additional environment information:

Expected behavior

Actual behavior

Steps to reproduce

Additional information

A workaround is to add __attribute__((nomips16)) to the function mbedtls_mpi_core_mla in bignum_core