[lld] r373255 - ELF: Don't merge SHF_LINK_ORDER sections for different output sections in relocatable links.
Peter Collingbourne via llvm-commits
llvm-commits at lists.llvm.org
Mon Sep 30 13:23:01 PDT 2019
Author: pcc
Date: Mon Sep 30 13:23:00 2019
New Revision: 373255
URL: http://llvm.org/viewvc/llvm-project?rev=373255&view=rev
Log:
ELF: Don't merge SHF_LINK_ORDER sections for different output sections in relocatable links.
Merging SHF_LINK_ORDER sections can affect semantics if the sh_link
fields point to different sections.
Specifically, for SHF_LINK_ORDER sections, the sh_link field acts as a reverse
dependency from the linked section, causing the SHF_LINK_ORDER section to
be included if the linked section is included. Merging sections with different
sh_link fields will cause the entire contents of the SHF_LINK_ORDER section
to be associated with a single (arbitrarily chosen) output section, whereas the
correct semantics are for the individual pieces of the SHF_LINK_ORDER section
to be associated with their linked output sections. As a result we can end up
incorrectly dropping SHF_LINK_ORDER section contents or including the wrong
section contents, depending on which linked sections were chosen.
Differential Revision: https://reviews.llvm.org/D68094
Added:
lld/trunk/test/ELF/relocatable-linkorder.s
Modified:
lld/trunk/ELF/LinkerScript.cpp
Modified: lld/trunk/ELF/LinkerScript.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/LinkerScript.cpp?rev=373255&r1=373254&r2=373255&view=diff
==============================================================================
--- lld/trunk/ELF/LinkerScript.cpp (original)
+++ lld/trunk/ELF/LinkerScript.cpp Mon Sep 30 13:23:00 2019
@@ -645,6 +645,20 @@ addInputSec(StringMap<TinyPtrVector<Outp
for (OutputSection *sec : v) {
if (sec->partition != isec->partition)
continue;
+
+ if (config->relocatable && (isec->flags & SHF_LINK_ORDER)) {
+ // Merging two SHF_LINK_ORDER sections with different sh_link fields will
+ // change their semantics, so we only merge them in -r links if they will
+ // end up being linked to the same output section. The casts are fine
+ // because everything in the map was created by the orphan placement code.
+ auto *firstIsec = cast<InputSectionBase>(
+ cast<InputSectionDescription>(sec->sectionCommands[0])
+ ->sectionBases[0]);
+ if (firstIsec->getLinkOrderDep()->getOutputSection() !=
+ isec->getLinkOrderDep()->getOutputSection())
+ continue;
+ }
+
sec->recordSection(isec);
return nullptr;
}
@@ -659,26 +673,30 @@ void LinkerScript::addOrphanSections() {
StringMap<TinyPtrVector<OutputSection *>> map;
std::vector<OutputSection *> v;
- auto add = [&](InputSectionBase *s) {
- if (!s->isLive() || s->parent)
- return;
-
- StringRef name = getOutputSectionName(s);
-
- if (config->orphanHandling == OrphanHandlingPolicy::Error)
- error(toString(s) + " is being placed in '" + name + "'");
- else if (config->orphanHandling == OrphanHandlingPolicy::Warn)
- warn(toString(s) + " is being placed in '" + name + "'");
-
- if (OutputSection *sec = findByName(sectionCommands, name)) {
- sec->recordSection(s);
- return;
+ std::function<void(InputSectionBase *)> add;
+ add = [&](InputSectionBase *s) {
+ if (s->isLive() && !s->parent) {
+ StringRef name = getOutputSectionName(s);
+
+ if (config->orphanHandling == OrphanHandlingPolicy::Error)
+ error(toString(s) + " is being placed in '" + name + "'");
+ else if (config->orphanHandling == OrphanHandlingPolicy::Warn)
+ warn(toString(s) + " is being placed in '" + name + "'");
+
+ if (OutputSection *sec = findByName(sectionCommands, name)) {
+ sec->recordSection(s);
+ } else {
+ if (OutputSection *os = addInputSec(map, s, name))
+ v.push_back(os);
+ assert(isa<MergeInputSection>(s) ||
+ s->getOutputSection()->sectionIndex == UINT32_MAX);
+ }
}
- if (OutputSection *os = addInputSec(map, s, name))
- v.push_back(os);
- assert(isa<MergeInputSection>(s) ||
- s->getOutputSection()->sectionIndex == UINT32_MAX);
+ if (config->relocatable)
+ for (InputSectionBase *depSec : s->dependentSections)
+ if (depSec->flags & SHF_LINK_ORDER)
+ add(depSec);
};
// For futher --emit-reloc handling code we need target output section
@@ -686,6 +704,12 @@ void LinkerScript::addOrphanSections() {
// to create target sections first. We do not want priority handling
// for synthetic sections because them are special.
for (InputSectionBase *isec : inputSections) {
+ // In -r links, SHF_LINK_ORDER sections are added while adding their parent
+ // sections because we need to know the parent's output section before we
+ // can select an output section for the SHF_LINK_ORDER section.
+ if (config->relocatable && (isec->flags & SHF_LINK_ORDER))
+ continue;
+
if (auto *sec = dyn_cast<InputSection>(isec))
if (InputSectionBase *rel = sec->getRelocatedSection())
if (auto *relIS = dyn_cast_or_null<InputSectionBase>(rel->parent))
Added: lld/trunk/test/ELF/relocatable-linkorder.s
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/relocatable-linkorder.s?rev=373255&view=auto
==============================================================================
--- lld/trunk/test/ELF/relocatable-linkorder.s (added)
+++ lld/trunk/test/ELF/relocatable-linkorder.s Mon Sep 30 13:23:00 2019
@@ -0,0 +1,36 @@
+// REQUIRES: x86
+// RUN: llvm-mc %s -o %t.o -filetype=obj --triple=x86_64-unknown-linux
+// RUN: ld.lld %t.o -o %t -r
+// RUN: llvm-readelf -S %t | FileCheck --check-prefix=DIFFERENT %s
+// RUN: echo 'SECTIONS { .text.f1 : { *(.text.f1) } .text.f2 : { *(.text.f2) } }' > %t.lds
+// RUN: ld.lld %t.o -o %t -r %t.lds
+// RUN: llvm-readelf -S %t | FileCheck --check-prefix=DIFFERENT %s
+// RUN: echo 'SECTIONS { .text : { *(.text.f1) *(.text.f2) } }' > %t.lds
+// RUN: ld.lld %t.o -o %t -r %t.lds
+// RUN: llvm-readelf -S -x foo %t | FileCheck --check-prefix=SAME %s
+
+/// Test that SHF_LINK_ORDER sections with different linked sections
+/// aren't merged.
+
+.section .text.f1,"ax", at progbits
+.globl f1
+f1:
+ret
+
+.section .text.f2,"ax", at progbits
+.globl f2
+f2:
+ret
+
+// SAME: foo
+// DIFFERENT: foo
+.section foo,"ao", at progbits,.text.f2,unique,2
+.quad 2
+
+// SAME-NOT: foo
+// DIFFERENT: foo
+.section foo,"ao", at progbits,.text.f1,unique,1
+.quad 1
+
+// SAME: Hex dump of section 'foo':
+// SAME: 01000000 00000000 02000000 00000000
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