CODEWITHSUNDEEP
gccinline-assembly
ctuffli
ctuffli

Reputation: 3580

How to use __func__ with inline assembly

I'm trying to add meta-data to an ELF executable by storing strings in a special section (__dlog). The current approach uses (abuses?) inline assembly to store the strings and nearly works as desired.

#include <stdio.h>
#include <stdlib.h>

#define DLOG(proto...) \
        __asm__(".pushsection __dlog, \"S\", @note\n\t" \
                ".asciz \"" __FILE__ ":function_name_here:" #proto "\"\n\t" \
                ".popsection\n\t" )

int
foo(int bar)
{
    int baz = bar / 2;
    DLOG(int baz);
    return baz;
}

int
main(int argc, char *argv[])
{
    foo(argc);
    return EXIT_SUCCESS;
}

But ideally, the macro should automatically include the function name as a part of the string by taking advantage of the __func__ identifier. The end result should be the string

file.c:foo:int baz\0

in a section called __dlog. But since __func__ is not a string literal, gcc complains with this code

".asciz \"" __FILE__ ":" __func__ ":" #proto "\"\n\t"

Is there anyway to get the contents of __func__ added to the string? Bonus points if the solution doesn't require custom build options or post-processing steps. Compiler is gcc 4.4 and 4.5.

Upvotes: 3

Views: 1455

Answers (1)

KitsuneYMG
KitsuneYMG

Reputation: 12901

Edit: This seems to work, it doesn't give a completely un-mangled name, but the function name is there

#define DLOG( proto...) \
__asm__(".pushsection __dlog, \"S\", @note\n\t" \
                ".asciz \"" __FILE__ ":%0:" #proto "\"\n\t" \
                ".popsection\n\t"  \
 : \
 :  "s" ( __func__ ) )


int main(int argc, char*argv[]) {
DLOG(int argc, char*argv[]);

return 0;
}

extern "C" void test(int bar) {
DLOG(bar);
}

g++-4.4 test.cpp && xxd a.out | less -p test.cpp

0001020: 7465 7374 2e63 7070 3a24 5f5a 5a34 6d61  test.cpp:$_ZZ4ma
0001030: 696e 4538 5f5f 6675 6e63 5f5f 3a69 6e74  inE8__func__:int
0001040: 2061 7267 632c 2063 6861 722a 6172 6776   argc, char*argv
0001050: 5b5d 0074 6573 742e 6370 703a 245f 5a5a  [].test.cpp:$_ZZ
0001060: 3474 6573 7445 385f 5f66 756e 635f 5f3a  4testE8__func__:
0001070: 6261 7200 4743 433a 2028 5562 756e 7475  bar.GCC: (Ubuntu

Original Answer:

In gcc-3.3 using c mode, __func__ is treated like a const char []. If c++ mode, and in gcc > 3.3, __func__ is always a variable.

I guess you could use an older version of gcc, in c-mode, to accomplish this.

See the last paragraph on http://gcc.gnu.org/onlinedocs/gcc/Function-Names.html

Upvotes: 3

Related Questions