caio/clang-p2996
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ELF: Don't create sections for section header index 0

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Summary:
The first section header does not define a real section. Instead it is
used for various elf extensions. This patch skips creation of a section
for index 0.

This has one furtunate side-effect, in that it allows us to use the section
header index as the Section ID (where 0 is also invalid). This way, we
can get rid of a lot of spurious +1s in the ObjectFileELF code.

Reviewers: clayborg, krytarowski, joerg, espindola

Subscribers: emaste, lldb-commits, arichardson

Differential Revision: https://reviews.llvm.org/D55757

llvm-svn: 349498
This commit is contained in:
Pavel Labath
2018-12-18 15:56:45 +00:00
parent 94d2d09c76
commit 0d38e4fd2c
5 changed files with 24 additions and 24 deletions
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36
lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp
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@@ -889,11 +889,11 @@ AddressClass ObjectFileELF::GetAddressClass(addr_t file_addr) {
}
size_t ObjectFileELF::SectionIndex(const SectionHeaderCollIter &I) {
return std::distance(m_section_headers.begin(), I) + 1u;
return std::distance(m_section_headers.begin(), I);
}
size_t ObjectFileELF::SectionIndex(const SectionHeaderCollConstIter &I) const {
return std::distance(m_section_headers.begin(), I) + 1u;
return std::distance(m_section_headers.begin(), I);
}
bool ObjectFileELF::ParseHeader() {
@@ -1081,7 +1081,7 @@ size_t ObjectFileELF::ParseDependentModules() {
return 0;
// sh_link: section header index of string table used by entries in the
// section.
Section *dynstr = section_list->FindSectionByID(header->sh_link + 1).get();
Section *dynstr = section_list->FindSectionByID(header->sh_link).get();
if (!dynstr)
return 0;
@@ -1717,10 +1717,10 @@ size_t ObjectFileELF::ParseSectionHeaders() {
const ObjectFileELF::ELFSectionHeaderInfo *
ObjectFileELF::GetSectionHeaderByIndex(lldb::user_id_t id) {
if (!id || !ParseSectionHeaders())
if (!ParseSectionHeaders())
return NULL;
if (--id < m_section_headers.size())
if (id < m_section_headers.size())
return &m_section_headers[id];
return NULL;
@@ -1853,7 +1853,7 @@ void ObjectFileELF::CreateSections(SectionList &unified_section_list) {
m_sections_ap.reset(new SectionList());
VMAddressProvider address_provider(CalculateType());
for (SectionHeaderCollIter I = m_section_headers.begin();
for (SectionHeaderCollIter I = std::next(m_section_headers.begin());
I != m_section_headers.end(); ++I) {
const ELFSectionHeaderInfo &header = *I;
@@ -1990,9 +1990,9 @@ unsigned ObjectFileELF::ParseSymbols(Symtab *symtab, user_id_t start_id,
SectionSP symbol_section_sp;
SymbolType symbol_type = eSymbolTypeInvalid;
Elf64_Half section_idx = symbol.st_shndx;
Elf64_Half shndx = symbol.st_shndx;
switch (section_idx) {
switch (shndx) {
case SHN_ABS:
symbol_type = eSymbolTypeAbsolute;
break;
@@ -2000,7 +2000,7 @@ unsigned ObjectFileELF::ParseSymbols(Symtab *symtab, user_id_t start_id,
symbol_type = eSymbolTypeUndefined;
break;
default:
symbol_section_sp = section_list->GetSectionAtIndex(section_idx);
symbol_section_sp = section_list->FindSectionByID(shndx);
break;
}
@@ -2169,7 +2169,7 @@ unsigned ObjectFileELF::ParseSymbols(Symtab *symtab, user_id_t start_id,
// symbols. See above for more details.
uint64_t symbol_value = symbol.st_value + symbol_value_offset;
if (symbol_section_sp == nullptr && section_idx == SHN_ABS &&
if (symbol_section_sp == nullptr && shndx == SHN_ABS &&
symbol.st_size != 0) {
// We don't have a section for a symbol with non-zero size. Create a new
// section for it so the address range covered by the symbol is also
@@ -2282,9 +2282,8 @@ unsigned ObjectFileELF::ParseSymbolTable(Symtab *symbol_table,
assert(symtab_hdr->sh_type == SHT_SYMTAB ||
symtab_hdr->sh_type == SHT_DYNSYM);
// sh_link: section header index of associated string table. Section ID's are
// ones based.
user_id_t strtab_id = symtab_hdr->sh_link + 1;
// sh_link: section header index of associated string table.
user_id_t strtab_id = symtab_hdr->sh_link;
Section *strtab = section_list->FindSectionByID(strtab_id).get();
if (symtab && strtab) {
@@ -2494,10 +2493,6 @@ ObjectFileELF::ParseTrampolineSymbols(Symtab *symbol_table, user_id_t start_id,
if (!symtab_id || !plt_id)
return 0;
// Section ID's are ones based;
symtab_id++;
plt_id++;
const ELFSectionHeaderInfo *plt_hdr = GetSectionHeaderByIndex(plt_id);
if (!plt_hdr)
return 0;
@@ -2523,7 +2518,7 @@ ObjectFileELF::ParseTrampolineSymbols(Symtab *symbol_table, user_id_t start_id,
return 0;
// sh_link points to associated string table.
Section *strtab = section_list->FindSectionByID(sym_hdr->sh_link + 1).get();
Section *strtab = section_list->FindSectionByID(sym_hdr->sh_link).get();
if (!strtab)
return 0;
@@ -2651,9 +2646,8 @@ unsigned ObjectFileELF::RelocateDebugSections(const ELFSectionHeader *rel_hdr,
if (!section_list)
return 0;
// Section ID's are ones based.
user_id_t symtab_id = rel_hdr->sh_link + 1;
user_id_t debug_id = rel_hdr->sh_info + 1;
user_id_t symtab_id = rel_hdr->sh_link;
user_id_t debug_id = rel_hdr->sh_info;
const ELFSectionHeader *symtab_hdr = GetSectionHeaderByIndex(symtab_id);
if (!symtab_hdr)