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Treat STV_HIDDEN and STV_INTERNAL symbols as STB_LOCAL 

In a reference to PR ld/19908 make ld.so respect symbol export classes
aka visibility and treat STV_HIDDEN and STV_INTERNAL symbols as local,
preventing such symbols from preempting exported symbols.

According to the ELF gABI[1] neither STV_HIDDEN nor STV_INTERNAL symbols
are supposed to be present in linked binaries:

"A hidden symbol contained in a relocatable object must be either
removed or converted to STB_LOCAL binding by the link-editor when the
relocatable object is included in an executable file or shared object."

"An internal symbol contained in a relocatable object must be either
removed or converted to STB_LOCAL binding by the link-editor when the
relocatable object is included in an executable file or shared object."

however some GNU binutils versions produce such symbols in some cases.
PR ld/19908 is one and we also have this note in scripts/abilist.awk:

so clearly there is linked code out there which contains such symbols
which is prone to symbol table misinterpretation, and it'll be more
productive if we handle this gracefully, under the Robustness Principle:
"be liberal in what you accept, and conservative in what you produce",
especially as this is a simple (STV_HIDDEN|STV_INTERNAL) => STB_LOCAL
mapping.

References:

[1] "System V Application Binary Interface - DRAFT - 24 April 2001",
    The Santa Cruz Operation, Inc., "Symbol Table",
    <http://www.sco.com/developers/gabi/2001-04-24/ch4.symtab.html>

	* sysdeps/generic/ldsodefs.h
	(dl_symbol_visibility_binds_local_p): New inline function.
	* elf/dl-addr.c (determine_info): Treat hidden and internal
	symbols as local.
	* elf/dl-lookup.c (do_lookup_x): Likewise.
	* elf/dl-reloc.c (RESOLVE_MAP): Likewise.
This commit is contained in:
Maciej W. Rozycki 2016-05-07 02:29:54 +01:00
parent 2cbec36566
commit b6084a958f
5 changed files with 29 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

9
ChangeLog
View File

@ -1,3 +1,12 @@
2016-07-01 Maciej W. Rozycki <macro@imgtec.com>
* sysdeps/generic/ldsodefs.h
(dl_symbol_visibility_binds_local_p): New inline function.
* elf/dl-addr.c (determine_info): Treat hidden and internal
symbols as local.
* elf/dl-lookup.c (do_lookup_x): Likewise.
* elf/dl-reloc.c (RESOLVE_MAP): Likewise.
2016-07-01 Aurelien Jarno <aurelien@aurel32.net>
* sparc/sparc32/sparcv9/fpu/s_nearbyint.S (__nearbyint): Trigger an

1
elf/dl-addr.c
View File

@ -88,6 +88,7 @@ determine_info (const ElfW(Addr) addr, struct link_map *match, Dl_info *info,
for (; (void *) symtab < (void *) symtabend; ++symtab)
if ((ELFW(ST_BIND) (symtab->st_info) == STB_GLOBAL
|| ELFW(ST_BIND) (symtab->st_info) == STB_WEAK)
&& __glibc_likely (!dl_symbol_visibility_binds_local_p (symtab))
&& ELFW(ST_TYPE) (symtab->st_info) != STT_TLS
&& (symtab->st_shndx != SHN_UNDEF
|| symtab->st_value != 0)

4
elf/dl-lookup.c
View File

@ -516,6 +516,10 @@ do_lookup_x (const char *undef_name, uint_fast32_t new_hash,
#endif
}
/* Hidden and internal symbols are local, ignore them. */
if (__glibc_unlikely (dl_symbol_visibility_binds_local_p (sym)))
goto skip;
switch (ELFW(ST_BIND) (sym->st_info))
{
case STB_WEAK:

3
elf/dl-reloc.c
View File

@ -233,7 +233,8 @@ _dl_relocate_object (struct link_map *l, struct r_scope_elem *scope[],
/* This macro is used as a callback from the ELF_DYNAMIC_RELOCATE code. */
#define RESOLVE_MAP(ref, version, r_type) \
(ELFW(ST_BIND) ((*ref)->st_info) != STB_LOCAL \
((ELFW(ST_BIND) ((*ref)->st_info) != STB_LOCAL \
&& __glibc_likely (!dl_symbol_visibility_binds_local_p (*ref))) \
? ((__builtin_expect ((*ref) == l->l_lookup_cache.sym, 0) \
&& elf_machine_type_class (r_type) == l->l_lookup_cache.type_class) \
? (bump_num_cache_relocations (), \

13
sysdeps/generic/ldsodefs.h
View File

@ -88,6 +88,19 @@ typedef struct link_map *lookup_t;
|| (ADDR) < (L)->l_addr + (SYM)->st_value + (SYM)->st_size) \
&& ((MATCHSYM) == NULL || (MATCHSYM)->st_value < (SYM)->st_value))
/* According to the ELF gABI no STV_HIDDEN or STV_INTERNAL symbols are
expected to be present in dynamic symbol tables as they should have
been either removed or converted to STB_LOCAL binding by the static
linker. However some GNU binutils versions produce such symbols in
some cases. To prevent such symbols present in a buggy binary from
preempting global symbols we filter them out with this predicate. */
static __always_inline bool
dl_symbol_visibility_binds_local_p (const ElfW(Sym) *sym)
{
return (ELFW(ST_VISIBILITY) (sym->st_other) == STV_HIDDEN
|| ELFW(ST_VISIBILITY) (sym->st_other) == STV_INTERNAL);
}
/* Unmap a loaded object, called by _dl_close (). */
#ifndef DL_UNMAP_IS_SPECIAL
# define DL_UNMAP(map) _dl_unmap_segments (map)