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Fix bug with relocation addends and merge sections with --icf.

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During --icf processing, gold was incorrectly processing the relocation
addend for references to items in a merge section. PC-relative references
and other forms of reference with a biased base address require a
non-section local symbol, where the addend is purely the bias.

gold/
	PR gold/20642
	PR gold/22820
	* gc.h (gc_process_relocs): Flag STT_SECTION symbols in symvec.
	* icf.cc (get_section_contents): For merge sections, ignore the
	addend for relocations against non-section symbols.
This commit is contained in:
Cary Coutant 2018-04-24 21:57:37 -07:00
parent 2ac93be706
commit 651d162038
3 changed files with 65 additions and 28 deletions
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8
gold/ChangeLog
View File

@ -1,3 +1,11 @@
2018-04-24 Cary Coutant <ccoutant@gmail.com>
PR gold/20642
PR gold/22820
* gc.h (gc_process_relocs): Flag STT_SECTION symbols in symvec.
* icf.cc (get_section_contents): For merge sections, ignore the
addend for relocations against non-section symbols.
2018-04-24 Cary Coutant <ccoutant@gmail.com>
PR gold/16504

7
gold/gc.h
View File

@ -247,7 +247,12 @@ gc_process_relocs(
(*secvec).push_back(Section_id(src_obj, dst_indx));
else
(*secvec).push_back(Section_id(NULL, 0));
(*symvec).push_back(NULL);
// If the target of the relocation is an STT_SECTION symbol,
// make a note of that by storing -1 in the symbol vector.
if (lsym.get_st_type() == elfcpp::STT_SECTION)
(*symvec).push_back(reinterpret_cast<Symbol*>(-1));
else
(*symvec).push_back(NULL);
(*addendvec).push_back(std::make_pair(
static_cast<long long>(symvalue),
static_cast<long long>(addend)));

78
gold/icf.cc
View File

@ -327,6 +327,16 @@ get_section_contents(bool first_iteration,
for (; it_v != v.end(); ++it_v, ++it_s, ++it_a, ++it_o, ++it_addend_size)
{
Symbol* gsym = *it_s;
bool is_section_symbol = false;
// A -1 value in the symbol vector indicates a local section symbol.
if (gsym == reinterpret_cast<Symbol*>(-1))
{
is_section_symbol = true;
gsym = NULL;
}
if (first_iteration
&& it_v->first != NULL)
{
@ -354,7 +364,7 @@ get_section_contents(bool first_iteration,
// It would be nice if we could use format macros in inttypes.h
// here but there are not in ISO/IEC C++ 1998.
snprintf(addend_str, sizeof(addend_str), "%llx %llx %llux",
snprintf(addend_str, sizeof(addend_str), "%llx %llx %llx",
static_cast<long long>((*it_a).first),
static_cast<long long>((*it_a).second),
static_cast<unsigned long long>(*it_o));
@ -367,8 +377,8 @@ get_section_contents(bool first_iteration,
if (first_iteration)
{
// If the symbol name is available, use it.
if ((*it_s) != NULL)
buffer.append((*it_s)->name());
if (gsym != NULL)
buffer.append(gsym->name());
// Append the addend.
buffer.append(addend_str);
buffer.append("@");
@ -395,10 +405,10 @@ get_section_contents(bool first_iteration,
symtab->icf()->section_to_int_map();
Icf::Uniq_secn_id_map::iterator section_id_map_it =
section_id_map.find(reloc_secn);
bool is_sym_preemptible = (*it_s != NULL
&& !(*it_s)->is_from_dynobj()
&& !(*it_s)->is_undefined()
&& (*it_s)->is_preemptible());
bool is_sym_preemptible = (gsym != NULL
&& !gsym->is_from_dynobj()
&& !gsym->is_undefined()
&& gsym->is_preemptible());
if (!is_sym_preemptible
&& section_id_map_it != section_id_map.end())
{
@ -436,27 +446,41 @@ get_section_contents(bool first_iteration,
uint64_t entsize =
(it_v->first)->section_entsize(it_v->second);
long long offset = it_a->first;
// Handle SHT_RELA and SHT_REL addends, only one of these
// addends exists.
// Get the SHT_RELA addend. For RELA relocations, we have
// the addend from the relocation.
uint64_t reloc_addend_value = it_a->second;
// Handle SHT_REL addends.
// For REL relocations, we need to fetch the addend from the
// section contents.
const unsigned char* reloc_addend_ptr =
contents + static_cast<unsigned long long>(*it_o);
// Handle SHT_RELA and SHT_REL addends. Only one of these
// addends exists. When pointing to a merge section, the
// addend only matters if it's relative to a section
// symbol. In order to unambiguously identify the target
// of the relocation, the compiler (and assembler) must use
// a local non-section symbol unless Symbol+Addend does in
// fact point directly to the target. (In other words,
// a bias for a pc-relative reference or a non-zero based
// access forces the use of a local symbol, and the addend
// is used only to provide that bias.)
uint64_t reloc_addend_value = 0;
if (is_section_symbol)
{
// Get the SHT_RELA addend. For RELA relocations,
// we have the addend from the relocation.
reloc_addend_value = it_a->second;
// Update the addend value with the SHT_REL addend if
// available.
get_rel_addend(reloc_addend_ptr, *it_addend_size,
&reloc_addend_value);
// Handle SHT_REL addends.
// For REL relocations, we need to fetch the addend
// from the section contents.
const unsigned char* reloc_addend_ptr =
contents + static_cast<unsigned long long>(*it_o);
// Ignore the addend when it is a negative value. See the
// comments in Merged_symbol_value::value in object.h.
if (reloc_addend_value < 0xffffff00)
offset = offset + reloc_addend_value;
// Update the addend value with the SHT_REL addend if
// available.
get_rel_addend(reloc_addend_ptr, *it_addend_size,
&reloc_addend_value);
// Ignore the addend when it is a negative value.
// See the comments in Merged_symbol_value::value
// in object.h.
if (reloc_addend_value < 0xffffff00)
offset = offset + reloc_addend_value;
}
section_size_type secn_len;
@ -517,10 +541,10 @@ get_section_contents(bool first_iteration,
}
buffer.append("@");
}
else if ((*it_s) != NULL)
else if (gsym != NULL)
{
// If symbol name is available use that.
buffer.append((*it_s)->name());
buffer.append(gsym->name());
// Append the addend.
buffer.append(addend_str);
buffer.append("@");