Re: need help about __stack_chk_guard

[Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>]

On 24/09/23 21:53, 陈金佳 via Libc-help wrote:
> hello, i am a developer from china and i have encountered a tricky problem in the current development process.
> I need to compile a dynamic library, but i don't want to use symbols with "@GLIBC in the dynamic library, because it needs to be used in different glibc runtime environments. Therefore, during the compilation and linking process, I used the -Wl,--wrap compilation option to change the  glibc symbols used to __wrap_xxxx. However, this method only works for functions. Because i must use "-fstack-protector-strong",the compiled dynamic library will add "__stack_chk_guard" symbol, which is an OBJECT and cannot be replaced. I hope to get some help from you.
> 1. Is there a way to replace "__stack_chk_guard" or remove "@GLIBC_2.4" from "__stack_chk_guard@GLIBC_2.4"?
> 2.If there is no way to replace it, is  "__stack_chk_guard" only avaliable in the GLIBC2.4 version within visible time?
> 
> thank you!

Afaik --wrap ld option works for any symbol:

$ cat > lib.c <<EOF
int foo = 42;
EOF
$ cat > version.script <<EOF
VERS_1.1 {
   global:
      foo;
};
EOF
$ gcc -Wall -fPIC -shared -o lib.so -Wl,--version-script=version.script lib.c
$ readelf -s lib.so | grep -w foo | head -n 1
     6: 0000000000004020     4 OBJECT  GLOBAL DEFAULT   20 foo@@VERS_1.1

$ cat > main.c <<EOF
#include <stdio.h>

extern int foo;

int __wrap_foo = 24;

int main (int argc, char *argv[])
{
  printf ("foo=%d\n", foo);
}
EOF

$ gcc -Wall main.c -o main -Wl,-rpath,`pwd` lib.so && ./main
foo=42

$ gcc -Wall main.c -o main -Wl,-rpath,`pwd` lib.so -Wl,--wrap=foo && ./main
foo=24