From cd6ae7ea5431c2b8f16201fb0e2c413bf8d2df06 Mon Sep 17 00:00:00 2001 From: Fangrui Song Date: Fri, 16 Apr 2021 11:26:39 -0700 Subject: Set the retain attribute on _elf_set_element if CC supports [BZ #27492] So that text_set_element/data_set_element/bss_set_element defined variables will be retained by the linker. Note: 'used' and 'retain' are orthogonal: 'used' makes sure the variable will not be optimized out; 'retain' prevents section garbage collection if the linker support SHF_GNU_RETAIN. GNU ld 2.37 and LLD 13 will support -z start-stop-gc which allow C identifier name sections to be GCed even if there are live __start_/__stop_ references. Without the change, there are some static linking problems, e.g. _IO_cleanup (libio/genops.c) may be discarded by ld --gc-sections, so stdout is not flushed on exit. Note: GCC may warning 'retain' attribute ignored while __has_attribute(retain) is 1 (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99587). Reviewed-by: H.J. Lu --- include/libc-symbols.h | 14 ++++++++++---- 1 file changed, 10 insertions(+), 4 deletions(-) (limited to 'include') diff --git a/include/libc-symbols.h b/include/libc-symbols.h index 546fc26a7b..127ea656c2 100644 --- a/include/libc-symbols.h +++ b/include/libc-symbols.h @@ -352,6 +352,12 @@ for linking") */ +#ifdef HAVE_GNU_RETAIN +# define attribute_used_retain __attribute__ ((__used__, __retain__)) +#else +# define attribute_used_retain __attribute__ ((__used__)) +#endif + /* Symbol set support macros. */ /* Make SYMBOL, which is in the text segment, an element of SET. */ @@ -367,12 +373,12 @@ for linking") /* When building a shared library, make the set section writable, because it will need to be relocated at run time anyway. */ # define _elf_set_element(set, symbol) \ - static const void *__elf_set_##set##_element_##symbol##__ \ - __attribute__ ((used, section (#set))) = &(symbol) + static const void *__elf_set_##set##_element_##symbol##__ \ + attribute_used_retain __attribute__ ((section (#set))) = &(symbol) #else # define _elf_set_element(set, symbol) \ - static const void *const __elf_set_##set##_element_##symbol##__ \ - __attribute__ ((used, section (#set))) = &(symbol) + static const void *const __elf_set_##set##_element_##symbol##__ \ + attribute_used_retain __attribute__ ((section (#set))) = &(symbol) #endif /* Define SET as a symbol set. This may be required (it is in a.out) to -- cgit v1.2.3