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[ELF] Move SHT_REL/SHT_RELA handling from createInputSection to initializeSections

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This simplifies the code a bit. While here,

* change the `multiple relocation sections` diagnostic from `fatal` to `error` and include the relocated section name.
* drop less useful name from `getRelocTarget`. Without -r/--emit-relocs we don't need to get SHT_REL/SHT_RELA names.
This commit is contained in:
Fangrui Song 2022-01-18 23:31:51 -08:00
parent 41d05e29c0
commit 288082d45d
4 changed files with 54 additions and 63 deletions
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107
lld/ELF/InputFiles.cpp
View File

@ -643,12 +643,52 @@ void ObjFile<ELFT>::initializeSections(bool ignoreComdats) {
continue;
const Elf_Shdr &sec = objSections[i];
if (sec.sh_type == SHT_REL || sec.sh_type == SHT_RELA)
this->sections[i] = createInputSection(i, sec, shstrtab);
if (sec.sh_type == SHT_REL || sec.sh_type == SHT_RELA) {
// Find a relocation target section and associate this section with that.
// Target may have been discarded if it is in a different section group
// and the group is discarded, even though it's a violation of the spec.
// We handle that situation gracefully by discarding dangling relocation
// sections.
const uint32_t info = sec.sh_info;
InputSectionBase *s = getRelocTarget(i, sec, info);
if (!s)
continue;
// ELF spec allows mergeable sections with relocations, but they are rare,
// and it is in practice hard to merge such sections by contents, because
// applying relocations at end of linking changes section contents. So, we
// simply handle such sections as non-mergeable ones. Degrading like this
// is acceptable because section merging is optional.
if (auto *ms = dyn_cast<MergeInputSection>(s)) {
s = make<InputSection>(ms->file, ms->flags, ms->type, ms->alignment,
ms->data(), ms->name);
sections[info] = s;
}
if (s->relSecIdx != 0)
error(
toString(s) +
": multiple relocation sections to one section are not supported");
s->relSecIdx = i;
// Relocation sections are usually removed from the output, so return
// `nullptr` for the normal case. However, if -r or --emit-relocs is
// specified, we need to copy them to the output. (Some post link analysis
// tools specify --emit-relocs to obtain the information.)
if (config->copyRelocs) {
auto *isec = make<InputSection>(
*this, sec, check(obj.getSectionName(sec, shstrtab)));
// If the relocated section is discarded (due to /DISCARD/ or
// --gc-sections), the relocation section should be discarded as well.
s->dependentSections.push_back(isec);
sections[i] = isec;
}
continue;
}
// A SHF_LINK_ORDER section with sh_link=0 is handled as if it did not have
// the flag.
if (!(sec.sh_flags & SHF_LINK_ORDER) || !sec.sh_link)
if (!sec.sh_link || !(sec.sh_flags & SHF_LINK_ORDER))
continue;
InputSectionBase *linkSec = nullptr;
@ -828,9 +868,9 @@ template <class ELFT> static uint32_t readAndFeatures(const InputSection &sec) {
}
template <class ELFT>
InputSectionBase *ObjFile<ELFT>::getRelocTarget(uint32_t idx, StringRef name,
const Elf_Shdr &sec) {
uint32_t info = sec.sh_info;
InputSectionBase *ObjFile<ELFT>::getRelocTarget(uint32_t idx,
const Elf_Shdr &sec,
uint32_t info) {
if (info < this->sections.size()) {
InputSectionBase *target = this->sections[info];
@ -844,18 +884,11 @@ InputSectionBase *ObjFile<ELFT>::getRelocTarget(uint32_t idx, StringRef name,
return target;
}
error(toString(this) + Twine(": relocation section ") + name + " (index " +
Twine(idx) + ") has invalid sh_info (" + Twine(info) + ")");
error(toString(this) + Twine(": relocation section (index ") + Twine(idx) +
") has invalid sh_info (" + Twine(info) + ")");
return nullptr;
}
// Create a regular InputSection class that has the same contents
// as a given section.
static InputSection *toRegularSection(MergeInputSection *sec) {
return make<InputSection>(sec->file, sec->flags, sec->type, sec->alignment,
sec->data(), sec->name);
}
template <class ELFT>
InputSectionBase *ObjFile<ELFT>::createInputSection(uint32_t idx,
const Elf_Shdr &sec,
@ -908,10 +941,7 @@ InputSectionBase *ObjFile<ELFT>::createInputSection(uint32_t idx,
}
}
switch (sec.sh_type) {
case SHT_LLVM_DEPENDENT_LIBRARIES: {
if (config->relocatable)
break;
if (sec.sh_type == SHT_LLVM_DEPENDENT_LIBRARIES && !config->relocatable) {
ArrayRef<char> data =
CHECK(this->getObj().template getSectionContentsAsArray<char>(sec), this);
if (!data.empty() && data.back() != '\0') {
@ -927,45 +957,6 @@ InputSectionBase *ObjFile<ELFT>::createInputSection(uint32_t idx,
}
return &InputSection::discarded;
}
case SHT_RELA:
case SHT_REL: {
// Find a relocation target section and associate this section with that.
// Target may have been discarded if it is in a different section group
// and the group is discarded, even though it's a violation of the
// spec. We handle that situation gracefully by discarding dangling
// relocation sections.
InputSectionBase *target = getRelocTarget(idx, name, sec);
if (!target)
return nullptr;
// ELF spec allows mergeable sections with relocations, but they are
// rare, and it is in practice hard to merge such sections by contents,
// because applying relocations at end of linking changes section
// contents. So, we simply handle such sections as non-mergeable ones.
// Degrading like this is acceptable because section merging is optional.
if (auto *ms = dyn_cast<MergeInputSection>(target)) {
target = toRegularSection(ms);
this->sections[sec.sh_info] = target;
}
if (target->relSecIdx != 0)
fatal(toString(this) +
": multiple relocation sections to one section are not supported");
target->relSecIdx = idx;
// Relocation sections are usually removed from the output, so return
// `nullptr` for the normal case. However, if -r or --emit-relocs is
// specified, we need to copy them to the output. (Some post link analysis
// tools specify --emit-relocs to obtain the information.)
if (!config->copyRelocs)
return nullptr;
InputSection *relocSec = make<InputSection>(*this, sec, name);
// If the relocated section is discarded (due to /DISCARD/ or
// --gc-sections), the relocation section should be discarded as well.
target->dependentSections.push_back(relocSec);
return relocSec;
}
}
if (name.startswith(".n")) {
// The GNU linker uses .note.GNU-stack section as a marker indicating

4
lld/ELF/InputFiles.h
View File

@ -286,8 +286,8 @@ private:
void initializeSymbols();
void initializeJustSymbols();
InputSectionBase *getRelocTarget(uint32_t idx, StringRef name,
const Elf_Shdr &sec);
InputSectionBase *getRelocTarget(uint32_t idx, const Elf_Shdr &sec,
uint32_t info);
InputSectionBase *createInputSection(uint32_t idx, const Elf_Shdr &sec,
StringRef shstrtab);

4
lld/test/ELF/invalid/bad-reloc-target.test
View File

@ -1,6 +1,6 @@
# RUN: yaml2obj --docnum=1 %s -o %t1.o
# RUN: not ld.lld %t1.o -o /dev/null 2>&1 | FileCheck %s
# CHECK: error: {{.*}}.o: relocation section .rela.text (index 2) has invalid sh_info (0)
# CHECK: error: {{.*}}.o: relocation section (index 2) has invalid sh_info (0)
--- !ELF
FileHeader:
@ -25,7 +25,7 @@ Symbols:
# RUN: yaml2obj --docnum=2 %s -o %t2.o
# RUN: not ld.lld %t2.o -o /dev/null 2>&1 | FileCheck %s --check-prefix=ERR2
# ERR2: error: {{.*}}.o: relocation section .rela.text (index 2) has invalid sh_info (99)
# ERR2: error: {{.*}}.o: relocation section (index 2) has invalid sh_info (99)
--- !ELF
FileHeader:

2
lld/test/ELF/invalid/multiple-relocations-sections.test
View File

@ -1,6 +1,6 @@
# RUN: yaml2obj %s -o %t1.o
# RUN: not ld.lld %t1.o -o /dev/null 2>&1 | FileCheck %s
# CHECK: error: {{.*}}1.o: multiple relocation sections to one section are not supported
# CHECK: error: {{.*}}1.o:(.text): multiple relocation sections to one section are not supported
## The file has two relocation sections referring to a single target section.
## Multiple relocation sections to one section are not supported, check we report this case.