[Bug ld/19161] GNU ld wrongly garbage collects section referenced via __start_SECTIONNAME

[tmsriram at google dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=19161

Sriraman Tallam <tmsriram at google dot com> changed:

           What    |Removed                     |Added
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                 CC|                            |tmsriram at google dot com

--- Comment #1 from Sriraman Tallam <tmsriram at google dot com> ---
(In reply to David Li from comment #0)
> Here is a small reproducible:
> 
> // Failed with gnu ld
> 
> gcc -fuse-ld=bfd  -fdata-sections -Wl,--gc-sections gctest.c gctest2.c
> 
> /tmp/cc4jxArE.o: In function `dump':
> gctest2.c:(.text+0xc): undefined reference to `__start_my_section'


gold linker has this check to prevent any named section 'XXX' from being
garbage collected if it finds a symbol __start_XXX or __stop_XXX:

In gold/gc.h:

//If the symbol name matches '__start_XXX' then the section with
// the C identifier like name 'XXX' should not be garbage collected.
// A similar treatment to symbols with the name '__stop_XXX'.
if (is_prefix_of(cident_section_start_prefix, gsym->name()))
  { ...


GNU ld should also be doing this?


> collect2: error: ld returned 1 exit status
> 
> 
> // Fine with Gold:
> 
> gcc -fuse-ld=gold -fdata-sections -Wl,--gc-sections gctest.c gctest2.c
> 
> 
> 
> 
> // gctest.c
> 
> extern int variable;
> int main()
> {
>   return variable;
> }
> 
> 
> // gctest2.c
> 
> typedef struct A {
>    int i;
>    int j;
> } A;
> 
> extern int printf(const char*,...);
> extern int atexit(void (*)(void));
> A __attribute__((section("my_section"))) a[2] = {{1,2}, {3,4}};
> 
> extern A __start_my_section;
> extern A __stop_my_section;
> 
> int variable = 0;
> 
> 
> void dump()
> {
>    A* ap = &__start_my_section;
>    printf("%d %d\n", ap->i, ap->j);
> }
> 
> void __attribute__((constructor)) foo() {
>    atexit(dump);
> }

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