macOS下交叉编译AArch64程序时链接阶段失败求助

问题背景 #

在macOS上使用Clang搭配arm-linux-gnueabihf-binutils和LLVM工具交叉编译Hello World程序时，编译阶段可正常完成，但链接阶段报错，提示ld无法识别'/Users/rich/workspace/rpi/cross-test/build/main.o'的文件类型，尝试添加链接器参数后仍无效果。

链接失败输出 #

gcc build/main.o -o crosstest -L../sysroot/lib -L../sysroot/usr/local/lib -fuse-ld=ld -lc -lm
ld: unknown file type in '/Users/rich/workspace/rpi/cross-test/build/main.o'
clang: error: linker command failed with exit code 1 (use -v to see invocation)
gmake: *** [Makefile:88: crosstest] Error 1

Makefile内容 #

#######################################
# target: proto
#######################################
TARGET = crosstest

#######################################
# binaries
#######################################
GCC_PATH = gcc
PREFIX = 
CC = $(PREFIX)gcc
CXX = $(PREFIX)g++
AS = $(PREFIX)gcc -x assembler-with-cpp
CP = $(PREFIX)objcopy
SZ = $(PREFIX)size
HEX = $(CP) -O ihex
BIN = $(CP) -O binary -S

#######################################
# paths
#######################################
BUILD_DIR = build
SYSROOT = ../sysroot

#######################################
# options
#######################################
OPT = 
C_DEFS = 
CFLAGS = 

ifeq ($(DEBUG), 1)
OPT += -Og -g3
C_DEFS +=  -DDEBUG
$(info building for debug)
endif

ifeq ($(VERBOSE), 1)
OPT += -v
$(info verbose compile)
endif

#######################################
# compiler flags
#######################################
CFLAGS += $(OPT) $(C_DEFS) -Wall -Wextra -Wpedantic -std=c11 --sysroot=$(SYSROOT) -v --target=aarch64-unknown-linux-gnueabihf -pipe -mlittle-endian -munaligned-access -march=armv8-a
LDFLAGS = -L$(SYSROOT)/lib -L$(SYSROOT)/usr/local/lib -fuse-ld=ld
LDLIBS = -lc -lm

######################################
# source
######################################
C_SOURCES = \
$(wildcard *.c) \

C_INCLUDES =  \
-I. \
# -I../sysroot/usr/include \
# -I../sysroot/usr/local/include \

C_DEFS += \

# Create the build directory if it doesn't exist
$(BUILD_DIR):
    mkdir -p $(BUILD_DIR) 

# Create the necessary subdirectories in the build directory
$(BUILD_DIR)/%.o: %.c
    mkdir -p $(dir $@)
    $(CC) -c $(CFLAGS) $(C_INCLUDES) -c $< -o $@

# Compile the C source files into object files in the build directory
$(BUILD_DIR)/%.o: %.c | $(BUILD_DIR)
    $(CC) -c $(CFLAGS) $(C_INCLUDES) -c $< -o $@

# List of object files
C_OBJECTS = $(C_SOURCES:%.c=$(BUILD_DIR)/%.o)
CPP_OBJECTS = $(CPP_SOURCES:%.cpp=$(BUILD_DIR)/%.o)
OBJECTS = $(C_OBJECTS)

######################################
# build
######################################

all: $(TARGET) 

$(TARGET): $(OBJECTS)
    $(CC) $(OBJECTS) -o $@ $(LDFLAGS) $(LDLIBS)

clean: 
    rm -rf $(TARGET) $(BUILD_DIR)/*.o

编译器verbose输出 #

mkdir -p build/
gcc -c   -Wall -Wextra -Wpedantic -std=c11 --sysroot=../sysroot -v --target=aarch64-unknown-linux-gnueabihf -pipe -mlittle-endian -munaligned-access -march=armv8-a -I.  -c main.c -o build/main.o
Apple clang version 16.0.0 (clang-1600.0.26.6)
Target: aarch64-unknown-linux-gnueabihf
Thread model: posix
InstalledDir: /Library/Developer/CommandLineTools/usr/bin
 "/Library/Developer/CommandLineTools/usr/bin/clang" -cc1 -triple aarch64-unknown-linux-gnueabihf -emit-obj -mrelax-all -disable-free -clear-ast-before-backend -disable-llvm-verifier -discard-value-names -main-file-name main.c -mrelocation-model pic -pic-level 2 -pic-is-pie -mframe-pointer=non-leaf -fmath-errno -ffp-contract=on -fno-rounding-math -mconstructor-aliases -funwind-tables=2 -target-cpu generic -target-feature +neon -target-feature +v8a -target-abi aapcs -debugger-tuning=gdb -target-linker-version 1115.7.3 -v -fcoverage-compilation-dir=/Users/rich/workspace/rpi/cross-test -resource-dir /Library/Developer/CommandLineTools/usr/lib/clang/16 -I . -isysroot ../sysroot -internal-isystem /Library/Developer/CommandLineTools/usr/lib/clang/16/include -internal-isystem ../sysroot/usr/local/include -internal-externc-isystem ../sysroot/usr/include/aarch64-linux-gnu -internal-externc-isystem ../sysroot/include -internal-externc-isystem ../sysroot/usr/include -Wall -Wextra -Wpedantic -std=c11 -fdebug-compilation-dir=/Users/rich/workspace/rpi/cross-test -ferror-limit 19 -mdarwin-stkchk-strong-link -fno-signed-char -fgnuc-version=4.2.1 -fcolor-diagnostics -clang-vendor-feature=+disableAtImportPrivateFrameworkInImplementationError -target-feature -fmv -faddrsig -D__GCC_HAVE_DWARF2_CFI_ASM=1 -o build/main.o -x c main.c
clang -cc1 version 16.0.0 (clang-1600.0.26.6) default target arm64-apple-darwin24.2.0
ignoring nonexistent directory "../sysroot/include"
#include "..." search starts here:
#include <...> search starts here:
 .
 /Library/Developer/CommandLineTools/usr/lib/clang/16/include
 ../sysroot/usr/local/include
 ../sysroot/usr/include/aarch64-linux-gnu
 ../sysroot/usr/include
End of search list.
main.c:4:9: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
    4 | int main() {
      |         ^
      |          void
1 warning generated.
gcc build/main.o -o crosstest -L../sysroot/lib -L../sysroot/usr/local/lib -fuse-ld=ld -lc -lm
ld: unknown file type in '/Users/rich/workspace/rpi/cross-test/build/main.o'
clang: error: linker command failed with exit code 1 (use -v to see invocation)
gmake: *** [Makefile:88: crosstest] Error 1

解决方案 #

核心问题 #

当前使用的是macOS系统自带的ld（Mach-O格式链接器），它无法识别AArch64 Linux平台的ELF格式目标文件，导致链接失败。

修复步骤 #

1. 指定交叉编译工具链前缀：在Makefile中设置PREFIX为你的交叉编译工具链前缀（例如aarch64-linux-gnu-），确保调用对应平台的链接器而非系统自带工具：

   PREFIX = aarch64-linux-gnu-
   CC = $(PREFIX)gcc
   CXX = $(PREFIX)g++
   AS = $(PREFIX)gcc -x assembler-with-cpp
   CP = $(PREFIX)objcopy
   SZ = $(PREFIX)size
   

2. 移除强制指定系统ld的参数：交叉工具链会自动匹配对应平台的链接器，无需手动指定fuse-ld=ld，修改LDFLAGS：

   LDFLAGS = -L$(SYSROOT)/lib -L$(SYSROOT)/usr/local/lib
   

3. 验证工具链可用性：确保aarch64-linux-gnu-系列工具已安装并添加到环境变量PATH中，可通过aarch64-linux-gnu-ld --version确认工具正常。

验证修复 #

重新执行make命令，此时会使用交叉链接器处理ELF目标文件，可正常生成AArch64 Linux平台的可执行文件。

内容的提问来源于stack exchange，提问作者Richard Klosinski