linux - 尽管与存档有直接链接，但对任何 libc 符号的 undefined reference

Question

我正在使用 ARM-gcc 交叉编译器，在链接到 libc 中的任何实现时遇到问题。

Compiling prog.c, writing to prog.o...
~/.programs/arm-gcc/bin/arm-none-eabi-gcc -Wall -fno-common -mcpu=cortex-m4 -mthumb -O0 -g -DF_CPU=72000000 -I~/.programs/arm-gcc/arm-none-eabi/include -I../include -I. -I../src/include -c prog.c -o prog.o > prog.lst

Compiling ../common/sysinit.c, writing to sysinit.o...
~/.programs/arm-gcc/bin/arm-none-eabi-gcc -Wall -fno-common -mcpu=cortex-m4 -mthumb -O0 -g -DF_CPU=72000000 -I~/.programs/arm-gcc/arm-none-eabi/include -I../include -I. -I../src/include -c ../common/sysinit.c -o sysinit.o > sysinit.lst

Assembling ../common/crt0.s, writing to crt0.o...
~/.programs/arm-gcc/bin/arm-none-eabi-as -mcpu=cortex-m4 -o crt0.o ../common/crt0.s  > crt0.lst

Compiling uart.c, writing to uart.o...
~/.programs/arm-gcc/bin/arm-none-eabi-gcc -Wall -fno-common -mcpu=cortex-m4 -mthumb -O0 -g -DF_CPU=72000000 -I~/.programs/arm-gcc/arm-none-eabi/include -I../include -I. -I../src/include -c uart.c -o uart.o > uart.lst

~/.programs/arm-gcc/bin/arm-none-eabi-ld prog.o sysinit.o crt0.o uart.o -Map=prog.map -T../common/Teensy31_flash.ld -L~/.programs/arm-gcc/arm-none-eabi/lib  -o prog.elf
prog.o: In function `print_char':
/home/user/workspace/prog/src/prog.c:47: undefined reference to `sprintf'
/home/user/workspace/prog/src/prog.c:48: undefined reference to `printf'
/home/user/workspace/prog/src/prog.c:49: undefined reference to `strlen'
prog.o: In function `main':
/home/user/workspace/prog/src/prog.c:72: undefined reference to `memset'
make: *** [makefile:133: prog.elf] Error 1

我对 stdlib 进行了几次调用以说明这一点。我试图使用 -lc 明确链接到 libc，但遇到了:

/home/prog/.programs/arm-gcc/bin/arm-none-eabi-ld: cannot find -lc

存档目录是通过以下方式传递给链接器的:

L~/.programs/arm-gcc/arm-none-eabi/lib

我已经检查了这个目录的内容并验证了存档是否存在:

$ ls ~/.programs/arm-gcc/arm-none-eabi/lib
aprofile-validation.specs  libc_s.a            linux.specs
aprofile-ve.specs          libg.a              nano.specs
armv6-m                    libgloss-linux.a    nosys.specs
armv7-ar                   libg_s.a            pid.specs
armv7e-m                   libm.a              rdimon-crt0.o
armv7-m                    libnosys.a          rdimon.specs
cpu-init                   librdimon.a         rdpmon-crt0.o
crt0.o                     librdimon_s.a       rdpmon.specs
fpu                        librdpmon.a         redboot-crt0.o
iq80310.specs              libstdc++.a         redboot.ld
ldscripts                  libstdc++.a-gdb.py  redboot.specs
libarm_cortexM0l_math.a    libstdc++_s.a       redboot-syscalls.o
libarm_cortexM4lf_math.a   libsupc++.a         thumb
libarm_cortexM4l_math.a    libsupc++_s.a
libc.a                     linux-crt0.o

最后，libc 确实导出sprintf(和其他)

$ nm libc.a | grep "sprintf"
...
lib_a-sprintf.o:
00000000 T sprintf
00000000 T _sprintf_r
         U sprintf
         U _sprintf_r
...

---

关于我正在使用的 ARM-GCC 构建的信息:

$ ./arm-none-eabi-gcc -v
Using built-in specs.
COLLECT_GCC=./arm-none-eabi-gcc
COLLECT_LTO_WRAPPER=/home/user/.programs/arm-gcc/bin/../lib/gcc/arm-none-eabi/5.4.1/lto-wrapper
Target: arm-none-eabi
Configured with: /home/build/work/GCC-5-0-build/src/gcc/configure --target=arm-none-eabi --prefix=/home/build/work/GCC-5-0-build/install-native --libexecdir=/home/build/work/GCC-5-0-build/install-native/lib --infodir=/home/build/work/GCC-5-0-build/install-native/share/doc/gcc-arm-none-eabi/info --mandir=/home/build/work/GCC-5-0-build/install-native/share/doc/gcc-arm-none-eabi/man --htmldir=/home/build/work/GCC-5-0-build/install-native/share/doc/gcc-arm-none-eabi/html --pdfdir=/home/build/work/GCC-5-0-build/install-native/share/doc/gcc-arm-none-eabi/pdf --enable-languages=c,c++ --enable-plugins --disable-decimal-float --disable-libffi --disable-libgomp --disable-libmudflap --disable-libquadmath --disable-libssp --disable-libstdcxx-pch --disable-nls --disable-shared --disable-threads --disable-tls --with-gnu-as --with-gnu-ld --with-newlib --with-headers=yes --with-python-dir=share/gcc-arm-none-eabi --with-sysroot=/home/build/work/GCC-5-0-build/install-native/arm-none-eabi --build=i686-linux-gnu --host=i686-linux-gnu --with-gmp=/home/build/work/GCC-5-0-build/build-native/host-libs/usr --with-mpfr=/home/build/work/GCC-5-0-build/build-native/host-libs/usr --with-mpc=/home/build/work/GCC-5-0-build/build-native/host-libs/usr --with-isl=/home/build/work/GCC-5-0-build/build-native/host-libs/usr --with-cloog=/home/build/work/GCC-5-0-build/build-native/host-libs/usr --with-libelf=/home/build/work/GCC-5-0-build/build-native/host-libs/usr --with-host-libstdcxx='-static-libgcc -Wl,-Bstatic,-lstdc++,-Bdynamic -lm' --with-pkgversion='GNU Tools for ARM Embedded Processors' --with-multilib-list=armv6-m,armv7-m,armv7e-m,armv7-r,armv8-m.base,armv8-m.main
Thread model: single
gcc version 5.4.1 20160609 (release) [ARM/embedded-5-branch revision 237715] (GNU Tools for ARM Embedded Processors) 

Answer 1

-L~/.programs/arm-gcc/arm-none-eabi/lib 中的 ~ 没有展开。这是 shell that expands ~ into /home/user, but only when it is at the beginning of a word .

其实，这个-L选项是没有必要加的，因为gcc默认的搜索路径里已经有这个了。但是，您直接使用 ld 链接而不是使用 gcc。那不是一个好主意。最好与 gcc 链接并允许它添加默认搜索路径和其他所需的库，如 libc 和 libgcc。由于您提供了自己的 crt0，因此请将 -nostartfiles 添加到参数中。所以链接:

~/.programs/arm-gcc/bin/arm-none-eabi-gcc prog.o sysinit.o crt0.o uart.o \
    -Wl,-Map=prog.map -Wl,-T../common/Teensy31_flash.ld -nostartfiles -o prog.elf