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Fix build issues when compiling WAMRC as a cross-compiler #4112

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Fix build issues when compiling WAMRC as a cross-compiler #4112

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peter-tatrai
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Description

This pull request addresses issues encountered when compiling WAMRC to be a cross-compiler—running on a PC while targeting an embedded ARM platform. The key fixes include:

Fixes in This PR

  • -m32 compiler flag

    • The -m32 flag was previously added unconditionally for 32-bit targets, causing issues for non-x86 platforms.
    • Now, -m32 is only added when targeting a 32-bit x86 platform (X86_32), ensuring it is only applied where supported.

  • Improved PIC Flag Handling:

    • The logic for setting PIC (-fPIC) based on WAMR_BUILD_PLATFORM was overly complex.
    • This is now handled in CMake instead of using platform-specific conditions.

  • AOT Relocation Functions:

    • WAMRC previously included platform-specific headers (e.g., <arm_neon.h>) that are not available on a PC.
    • Since these AOT relocation functions are only used when executing AOT-compiled code (not by WAMRC itself), dummy versions have been introduced.
    • A more complete solution would be to split the code to avoid linking these functions altogether, but that would require more extensive changes.

  • SIMD Compilation Issues:

    • WAMRC attempted to include target platform-specific SIMD headers (e.g., ARM headers) when compiling on a different host platform (e.g., x86).
    • To address this, an option has been added to disable SIMD in WAMRC when cross-compiling.

@peter-tatrai
Use dummy AOT reloc functions when building wamrc
765795c 
AOT reloc functions are used only when loading AOT WebAssembly modules
on target, not during AOT compilation. Original code led to build issues
when building wamrc as cross-compiler, using arm header on x86 build.
@peter-tatrai
Add option to turn off SIMD support in wamrc
55bdc66
@calvin2021y
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hi @peter-tatrai

<arm_neon.h> is required at runtime ? if so maybe allow user set sysroot and triple by args will fix the problem.

@peter-tatrai
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The header file is required at compile-time, but this is not about cross-compiling wamrc—rather, it's about building a cross-compiler. In this scenario, we have both a host and a target architecture (e.g., host: x86_64, target: armv7). However, the CMake files currently use a single variable, WAMR_BUILD_PLATFORM, for both, even though it should only define the target platform. This causes issues, such as the one mentioned above.

With these commits and -DWAMR_BUILD_INVOKE_NATIVE_GENERAL=1 -DWAMR_BUILD_SIMD=0 -DWAMR_BUILD_TARGET=ARMv7, it is possible to build wamrc as a runnable binary on a PC while cross-compiling AOT modules for armv7.

lum1n0us
lum1n0us reviewed Mar 3, 2025
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wamr-compiler/CMakeLists.txt
@@ -275,6 +271,8 @@ else ()
message ("-- Lib wasi-threads disabled")
endif ()

set (WAMR_AOT_COMPILER 1)
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a similar naming pattern WAMR_BUILD_WAMR_COMPILER

wamr-compiler/CMakeLists.txt
set (CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -m32")
set (CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} -m32")
endif ()
# Add -m32 flag if compiling on 64-bit system for 32-bit x86 target
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I noticed that the information regarding Add -fPIC flag if build as 64-bit has been deleted. Was this done on purpose?

core/iwasm/aot/arch/aot_reloc_dummy.c
*/

#include "aot_reloc.h"
#include <stdlib.h>
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better remove <stdlib.h>. bh_platform.h in aot_runtime.h will do.

wamr-compiler/CMakeLists.txt
@@ -398,4 +396,4 @@ else()
${UV_A_LIBS})
endif()

install (TARGETS wamrc DESTINATION bin)
install (TARGETS wamrc)
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Was this done on purpose? Others might need it.

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@lum1n0us lum1n0us lum1n0us left review comments

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3 participants
@peter-tatrai @calvin2021y @lum1n0us