---- ---- ---- w.c
#include <stdio.h>
extern int debug_f __attribute__ ((weak));
int main(int, char *[]);
int main(int argc, char *argv[])
{
printf("flag %d", debug_f);
}
---- ---- ---- w.c
# ~/x-tools/arm-unknown-linux-gnueabi/bin/arm-unknown-linux-gnueabi-gcc
-march=armv7-a -o w w.c
# ~/x-tools/arm-unknown-linux-gnueabi/bin/arm-unknown-linux-gnueabi-readelf
-r w
Relocation section '.rel.dyn' at offset 0x270 contains 1 entries:
Offset Info Type Sym.Value Sym. Name
0002101c 00000315 R_ARM_GLOB_DAT 00000000 __gmon_start__
Relocation section '.rel.plt' at offset 0x278 contains 4 entries:
Offset Info Type Sym.Value Sym. Name
0002100c 00000116 R_ARM_JUMP_SLOT 00000000 printf@GLIBC_2.4
00021010 00000216 R_ARM_JUMP_SLOT 00000000 __libc_start_main@GLIBC_2.4
00021014 00000316 R_ARM_JUMP_SLOT 00000000 __gmon_start__
00021018 00000416 R_ARM_JUMP_SLOT 00000000 abort@GLIBC_2.4
There is no "debug_f" symbol.
Why not?
# ~/x-tools/arm-unknown-linux-gnueabi/bin/arm-unknown-linux-gnueabi-gcc
-march=armv7-a -c w.c
# ~/x-tools/arm-unknown-linux-gnueabi/bin/arm-unknown-linux-gnueabi-readelf
-r w.o
Relocation section '.rel.text' at offset 0x1dc contains 5 entries:
Offset Info Type Sym.Value Sym. Name
00000014 00000d2b R_ARM_MOVW_ABS_NC 00000000 debug_f
00000018 00000d2c R_ARM_MOVT_ABS 00000000 debug_f
00000024 0000072b R_ARM_MOVW_ABS_NC 00000000 .LC0
00000028 0000072c R_ARM_MOVT_ABS 00000000 .LC0
0000002c 00000e1c R_ARM_CALL 00000000 printf
There is a "debug_f" symbol in object file.
---- ---- ---- w2.c
extern void debug_info(void) __attribute__ ((weak));
int main(int, char *[]);
int main(int argc, char *argv[])
{
if (debug_info) {
debug_info();
}
}
---- ---- ----
# ~/x-tools/arm-unknown-linux-gnueabi/bin/arm-unknown-linux-gnueabi-gcc
-march=armv7-a -o w2 w2.c
# ~/x-tools/arm-unknown-linux-gnueabi/bin/arm-unknown-linux-gnueabi-readelf
-r w2
Relocation section '.rel.dyn' at offset 0x274 contains 1 entries:
Offset Info Type Sym.Value Sym. Name
0002101c 00000315 R_ARM_GLOB_DAT 00000000 __gmon_start__
Relocation section '.rel.plt' at offset 0x27c contains 4 entries:
Offset Info Type Sym.Value Sym. Name
0002100c 00000116 R_ARM_JUMP_SLOT 00000000 debug_info
00021010 00000216 R_ARM_JUMP_SLOT 00000000 __libc_start_main@GLIBC_2.4
00021014 00000316 R_ARM_JUMP_SLOT 00000000 __gmon_start__
00021018 00000416 R_ARM_JUMP_SLOT 00000000 abort@GLIBC_2.4
There is a debug_info symbol.
Variable is not good.
tool verison is
# ~/x-tools/arm-unknown-linux-gnueabi/bin/arm-unknown-linux-gnueabi-gcc -v
Using built-in specs.
COLLECT_GCC=/home/tanaka/x-tools/arm-unknown-linux-gnueabi/bin/arm-unknown-linux-gnueabi-gcc
COLLECT_LTO_WRAPPER=/home/tanaka/x-tools/arm-unknown-linux-gnueabi/libexec/gcc/arm-unknown-linux-gnueabi/6.3.0/lto-wrapper
Target: arm-unknown-linux-gnueabi
Configured with: /ftp/src/tools/.build/src/gcc-6.3.0/configure
--build=x86_64-build_pc-linux-gnu
--host=x86_64-build_pc-linux-gnu --target=arm-unknown-linux-gnueabi
--prefix=/home/tanaka/x-tools/arm-unknown-linux-gnueabi
--with-sysroot=/home/tanaka/x-tools/arm-unknown-linux-gnueabi/arm-unknown-linux-gnueabi/sysroot
--enable-languages=c
--with-pkgversion='crosstool-NG ' --enable-__cxa_atexit --enable-libmudflap
--enable-libgomp --enable-libssp
--disable-libquadmath --disable-libquadmath-support --disable-libsanitizer
--disable-libmpx
--with-gmp=/ftp/src/tools/.build/arm-unknown-linux-gnueabi/buildtools
--with-mpfr=/ftp/src/tools/.build/arm-unknown-linux-gnueabi/buildtools
--with-mpc=/ftp/src/tools/.build/arm-unknown-linux-gnueabi/buildtools
--with-isl=/ftp/src/tools/.build/arm-unknown-linux-gnueabi/buildtools
--enable-lto
--with-host-libstdcxx='-static-libgcc -Wl,-Bstatic,-lstdc++,-Bdynamic -lm'
--enable-threads=posix --enable-target-optspace --disable-plugin
--disable-nls
--enable-tls --disable-multilib
--with-local-prefix=/home/tanaka/x-tools/arm-unknown-linux-gnueabi/arm-unknown-linux-gnueabi/sysroot
--enable-long-long
Thread model: posix
gcc version 6.3.0 (crosstool-NG )
# ~/x-tools/arm-unknown-linux-gnueabi/bin/arm-unknown-linux-gnueabi-ld -v
GNU ld (crosstool-NG ) 2.28
--------
Katsuya TANAKA.
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