[ASan] Added .section statement to each function so they can be removed by --gc-sections.

[MaskRay]

LGTM

compiler-rt/lib/asan/asan_rtl_x86_64.S

17

If we don't support binutils<2.35 (compiler-rt is built by GCC), we may use .section .text,"ax",%progbits,unique,__COUNTER__ ;\ to save a few bytes in the string table.

How old GCC do we support for compiler-rt?

[MaskRay]

so they can be removed by --gc-sections.

This is not accurate. --gc-sections can apply to the monolithic .text with all callbacks. If all callbacks are unused, the whole .text is discarded.
It's probably just unrealistic for a large application where at least some are nearly guaranteed to be used.

Adding .section directives switches to fragmented text sections, which can be individually discarded.
Since we assume that a large portion of callbacks will not be called in a typical application, this can save a lot of space in the linker output.

[kstoimenov]

compiler-rt/lib/asan/asan_rtl_x86_64.S

17

Thanks for the hint. I will submit as because saving few bytes is not worth risking version complications.

compiler-rt/lib/asan/asan_rtl_x86_64.S

 #include "asan_mapping.h"
 #include "sanitizer_common/sanitizer_asm.h"
 
 #if defined(__x86_64__)
 #include "sanitizer_common/sanitizer_platform.h"
 
-.section .text
 .file "asan_rtl_x86_64.S"
 
 #define NAME(n, reg, op, s, i) n##_##op##_##i##_##s##_##reg
 
 #define FNAME(reg, op, s, i) NAME(__asan_check, reg, op, s, i)
 #define RLABEL(reg, op, s, i) NAME(.return, reg, op, s, i)
 #define CLABEL(reg, op, s, i) NAME(.check, reg, op, s, i)
 #define FLABEL(reg, op, s, i) NAME(.fail, reg, op, s, i)
 
 #define BEGINF(reg, op, s, i) \
+.section .text.FNAME(reg, op, s, i),"ax",@progbits ;\
 .globl  FNAME(reg, op, s, i) ;\
 ASM_TYPE_FUNCTION(FNAME(reg, op, s, i)) ;\
 .cfi_startproc ;\
 FNAME(reg, op, s, i): ;\
 
 #define ENDF .cfi_endproc ;\
 
 // Access check functions for 1,2 and 4 byte types, which require extra checks.