Imagelibrary/binutils-gdb
1
0
Fork 1
mirror of https://github.com/bminor/binutils-gdb.git synced 2025-12-26 17:18:55 +00:00
Code Issues Packages Projects Releases Wiki Activity

Fix treatment of symbol versions with unused as-needed libraries.

Browse Source 
When we have a weak reference to a symbol defined in an
as-needed library, and that library ends up not-needed, gold
simply clears the version information in the symbol table, even
if the symbol could have been resolved by a needed library later
in the link order. This results in a loss of version information,
which can cause the program to bind to the wrong version at run
time.

This patch lets a dynamic definition override an earlier one if
the earlier one is from a not-needed library, so that we can
retain the version information from the binding to the needed
library. In order to do that, the tracking of needed/not-needed
had to be moved up to symbol resolution time, instead of during
Symbol_table::set_dynsym_indexes().

In cases where we still end up discarding version information,
I've added a warning.

For the original problem report and discussion, see:

https://stackoverflow.com/questions/50751421/undefined-behavior-in-shared-lib-using-libpthread-but-not-having-it-in-elf-as-d

gold/
	* resolve.cc (Symbol_table::resolve): Rename tobinding to
	orig_tobinding.  Call set_is_needed() for objects that resolve
	non-weak references.
	(Symbol_table::should_override): Allow a dynamic definition to
	override an earlier one in a not-needed library.
	* symtab.cc (Symbol_table::set_dynsym_indexes): Remove separate
	processing for as-needed symbols.  Add warning when discarding
	version informatin.
	* testsuite/Makefile.am (weak_as_needed): New test case.
	* testsuite/Makefile.in: Regenerate.
	* testsuite/weak_as_needed.sh: New test script.
	* testsuite/weak_as_needed_a.c: New source file.
	* testsuite/weak_as_needed_b.c: New source file.
	* testsuite/weak_as_needed_b.script: New version script.
	* testsuite/weak_as_needed_c.c: New source file.
	* testsuite/weak_as_needed_c.script: New version script.
This commit is contained in:
Cary Coutant
2018-06-21 13:51:16 -07:00
parent 1ced1a5f10
commit cea6ffbd06
11 changed files with 246 additions and 35 deletions
Download Patch File Download Diff File Expand all files Collapse all files

37
gold/resolve.cc
View File

@@ -394,7 +394,7 @@ Symbol_table::resolve(Sized_symbol<size>* to,
object, &adjust_common_sizes,
&adjust_dyndef, is_default_version))
{
elfcpp::STB tobinding = to->binding();
elfcpp::STB orig_tobinding = to->binding();
typename Sized_symbol<size>::Value_type tovalue = to->value();
this->override(to, sym, st_shndx, is_ordinary, object, version);
if (adjust_common_sizes)
@@ -408,7 +408,7 @@ Symbol_table::resolve(Sized_symbol<size>* to,
{
// We are overriding an UNDEF or WEAK UNDEF with a DYN DEF.
// Remember which kind of UNDEF it was for future reference.
to->set_undef_binding(tobinding);
to->set_undef_binding(orig_tobinding);
}
}
else
@@ -431,6 +431,11 @@ Symbol_table::resolve(Sized_symbol<size>* to,
to->override_visibility(sym.get_st_visibility());
}
// If we have a non-WEAK reference from a regular object to a
// dynamic object, mark the dynamic object as needed.
if (to->is_from_dynobj() && to->in_reg() && !to->is_undef_binding_weak())
to->object()->set_is_needed();
if (adjust_common_sizes && parameters->options().warn_common())
{
if (tosize > sym.get_st_size())
@@ -621,6 +626,13 @@ Symbol_table::should_override(const Symbol* to, unsigned int frombits,
&& to->version() == NULL
&& is_default_version)
return true;
// Or, if the existing definition is in an unused --as-needed library,
// and the reference is weak, let the new definition override.
if (to->in_reg()
&& to->is_undef_binding_weak()
&& to->object()->as_needed()
&& !to->object()->is_needed())
return true;
return false;
case UNDEF * 16 + DYN_DEF:
@@ -637,16 +649,12 @@ Symbol_table::should_override(const Symbol* to, unsigned int frombits,
case COMMON * 16 + DYN_DEF:
case WEAK_COMMON * 16 + DYN_DEF:
case DYN_COMMON * 16 + DYN_DEF:
case DYN_WEAK_COMMON * 16 + DYN_DEF:
// Ignore a dynamic definition if we already have a common
// definition.
return false;
case DEF * 16 + DYN_WEAK_DEF:
case WEAK_DEF * 16 + DYN_WEAK_DEF:
case DYN_DEF * 16 + DYN_WEAK_DEF:
case DYN_WEAK_DEF * 16 + DYN_WEAK_DEF:
// Ignore a weak dynamic definition if we already have a
// definition.
return false;
@@ -670,12 +678,25 @@ Symbol_table::should_override(const Symbol* to, unsigned int frombits,
case COMMON * 16 + DYN_WEAK_DEF:
case WEAK_COMMON * 16 + DYN_WEAK_DEF:
case DYN_COMMON * 16 + DYN_WEAK_DEF:
case DYN_WEAK_COMMON * 16 + DYN_WEAK_DEF:
// Ignore a weak dynamic definition if we already have a common
// definition.
return false;
case DYN_COMMON * 16 + DYN_DEF:
case DYN_WEAK_COMMON * 16 + DYN_DEF:
case DYN_DEF * 16 + DYN_WEAK_DEF:
case DYN_WEAK_DEF * 16 + DYN_WEAK_DEF:
case DYN_COMMON * 16 + DYN_WEAK_DEF:
case DYN_WEAK_COMMON * 16 + DYN_WEAK_DEF:
// If the existing definition is in an unused --as-needed library,
// and the reference is weak, let a new dynamic definition override.
if (to->in_reg()
&& to->is_undef_binding_weak()
&& to->object()->as_needed()
&& !to->object()->is_needed())
return true;
return false;
case DEF * 16 + UNDEF:
case WEAK_DEF * 16 + UNDEF:
case UNDEF * 16 + UNDEF: