[lld] r359279 - [LLD][ELF] - Do not remove empty sections referenced in LOADADDR/ADDR commands.
George Rimar via llvm-commits
llvm-commits at lists.llvm.org
Thu Apr 25 23:59:30 PDT 2019
Author: grimar
Date: Thu Apr 25 23:59:30 2019
New Revision: 359279
URL: http://llvm.org/viewvc/llvm-project?rev=359279&view=rev
Log:
[LLD][ELF] - Do not remove empty sections referenced in LOADADDR/ADDR commands.
This is https://bugs.llvm.org//show_bug.cgi?id=38750.
If script references empty sections in LOADADDR/ADDR commands
.empty : { *(.empty ) }
.text : AT(LOADADDR (.empty) + SIZEOF (.empty)) { *(.text) }
then an empty section will be removed and LOADADDR/ADDR will evaluate to null.
It is not that user may expect from using of the generic script, what is a common case.
Differential revision: https://reviews.llvm.org/D54621
Added:
lld/trunk/test/ELF/linkerscript/empty-sections-expressions.test
Modified:
lld/trunk/ELF/LinkerScript.cpp
lld/trunk/ELF/OutputSections.h
lld/trunk/ELF/ScriptParser.cpp
Modified: lld/trunk/ELF/LinkerScript.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/LinkerScript.cpp?rev=359279&r1=359278&r2=359279&view=diff
==============================================================================
--- lld/trunk/ELF/LinkerScript.cpp (original)
+++ lld/trunk/ELF/LinkerScript.cpp Thu Apr 25 23:59:30 2019
@@ -825,12 +825,18 @@ static bool isDiscardable(OutputSection
if (!Sec.Phdrs.empty())
return false;
- // We do not want to remove sections that reference symbols in address and
- // other expressions. We add script symbols as undefined, and want to ensure
- // all of them are defined in the output, hence have to keep them.
+ // We do not want to remove OutputSections with expressions that reference
+ // symbols even if the OutputSection is empty. We want to ensure that the
+ // expressions can be evaluated and report an error if they cannot.
if (Sec.ExpressionsUseSymbols)
return false;
+ // OutputSections may be referenced by name in ADDR and LOADADDR expressions,
+ // as an empty Section can has a valid VMA and LMA we keep the OutputSection
+ // to maintain the integrity of the other Expression.
+ if (Sec.UsedInExpression)
+ return false;
+
for (BaseCommand *Base : Sec.SectionCommands) {
if (auto Cmd = dyn_cast<SymbolAssignment>(Base))
// Don't create empty output sections just for unreferenced PROVIDE
Modified: lld/trunk/ELF/OutputSections.h
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/OutputSections.h?rev=359279&r1=359278&r2=359279&view=diff
==============================================================================
--- lld/trunk/ELF/OutputSections.h (original)
+++ lld/trunk/ELF/OutputSections.h Thu Apr 25 23:59:30 2019
@@ -90,6 +90,7 @@ public:
bool NonAlloc = false;
bool Noload = false;
bool ExpressionsUseSymbols = false;
+ bool UsedInExpression = false;
bool InOverlay = false;
void finalize();
Modified: lld/trunk/ELF/ScriptParser.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/ScriptParser.cpp?rev=359279&r1=359278&r2=359279&view=diff
==============================================================================
--- lld/trunk/ELF/ScriptParser.cpp (original)
+++ lld/trunk/ELF/ScriptParser.cpp Thu Apr 25 23:59:30 2019
@@ -1154,6 +1154,7 @@ Expr ScriptParser::readPrimary() {
if (Tok == "ADDR") {
StringRef Name = readParenLiteral();
OutputSection *Sec = Script->getOrCreateOutputSection(Name);
+ Sec->UsedInExpression = true;
return [=]() -> ExprValue {
checkIfExists(Sec, Location);
return {Sec, false, 0, Location};
@@ -1230,6 +1231,7 @@ Expr ScriptParser::readPrimary() {
if (Tok == "LOADADDR") {
StringRef Name = readParenLiteral();
OutputSection *Cmd = Script->getOrCreateOutputSection(Name);
+ Cmd->UsedInExpression = true;
return [=] {
checkIfExists(Cmd, Location);
return Cmd->getLMA();
Added: lld/trunk/test/ELF/linkerscript/empty-sections-expressions.test
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/linkerscript/empty-sections-expressions.test?rev=359279&view=auto
==============================================================================
--- lld/trunk/test/ELF/linkerscript/empty-sections-expressions.test (added)
+++ lld/trunk/test/ELF/linkerscript/empty-sections-expressions.test Thu Apr 25 23:59:30 2019
@@ -0,0 +1,24 @@
+# REQUIRES: x86
+# RUN: echo ".text; nop; .data; .byte 0" \
+# RUN: | llvm-mc -filetype=obj -triple=x86_64-pc-linux - -o %t.o
+# RUN: ld.lld -o %t --script %s %t.o
+# RUN: llvm-readelf -program-headers %t | FileCheck %s
+
+## Check we do not remove the empty output sections used in LOADADDR/ADDR
+## expressions and hence can evaluate the correct addresses.
+
+# CHECK: Program Headers:
+# CHECK-NEXT: Type Offset VirtAddr PhysAddr
+# CHECK-NEXT: LOAD 0x001000 0x0000000000080000 0x0000000000080000
+# CHECK-NEXT: LOAD 0x001001 0x0000000000080001 0x0000000000082000
+
+# CHECK: Section to Segment mapping:
+# CHECK: 00 .empty .text
+# CHECK-NEXT: 01 .data
+
+SECTIONS {
+ . = 0x00080000;
+ .empty : { *(.empty ) }
+ .text : AT(LOADADDR(.empty) + SIZEOF(.empty)) { *(.text) }
+ .data : AT(ADDR(.empty) + 0x2000) { *(.data) }
+}
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