<div dir="ltr"><div class="gmail_extra"><div class="gmail_quote">On Mon, Mar 17, 2014 at 5:17 PM, Alexander Kornienko <span dir="ltr"><<a href="mailto:alexfh@google.com" target="_blank">alexfh@google.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">This commit breaks something in our code base. Unfortunately, I don't know what exactly and I'm struggling to come up with a reasonably-sized reproduction. Once I have something specific, I'll let you know.<div>
<div><br></div></div></div></blockquote><div>+David, who may be interested in this.</div><div><br></div><div>I've found a translation unit, which is handled differently before and after this revision. The difference is that after this revision, the functions marked with __attribute__((alias("..."))) loose the "function" flag (i.e. they get space instead of 'F' in the third column of the objdump -t output). Is this enough or you need more information to get this fixed?</div>
<div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div><div>
<div class="gmail_extra"><br><br><div class="gmail_quote">On Fri, Mar 14, 2014 at 9:09 PM, Rafael Espindola <span dir="ltr"><<a href="mailto:rafael.espindola@gmail.com" target="_blank">rafael.espindola@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Author: rafael<br>
Date: Fri Mar 14 15:09:04 2014<br>
New Revision: 203962<br>
<br>
URL: <a href="http://llvm.org/viewvc/llvm-project?rev=203962&view=rev" target="_blank">http://llvm.org/viewvc/llvm-project?rev=203962&view=rev</a><br>
Log:<br>
Correctly handle an ELF symbol defined with "a = b + expr".<br>
<br>
We were marking the symbol as absolute instead of computing b's offset + the<br>
expression value.<br>
<br>
This fixes pr19126.<br>
<br>
Added:<br>
llvm/trunk/test/MC/ELF/offset.s<br>
Modified:<br>
llvm/trunk/include/llvm/MC/MCSymbol.h<br>
llvm/trunk/lib/MC/ELFObjectWriter.cpp<br>
llvm/trunk/lib/MC/MCSymbol.cpp<br>
<br>
Modified: llvm/trunk/include/llvm/MC/MCSymbol.h<br>
URL: <a href="http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/MC/MCSymbol.h?rev=203962&r1=203961&r2=203962&view=diff" target="_blank">http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/MC/MCSymbol.h?rev=203962&r1=203961&r2=203962&view=diff</a><br>
==============================================================================<br>
--- llvm/trunk/include/llvm/MC/MCSymbol.h (original)<br>
+++ llvm/trunk/include/llvm/MC/MCSymbol.h Fri Mar 14 15:09:04 2014<br>
@@ -18,6 +18,7 @@<br>
#include "llvm/Support/Compiler.h"<br>
<br>
namespace llvm {<br>
+ class MCAsmLayout;<br>
class MCExpr;<br>
class MCSection;<br>
class MCContext;<br>
@@ -145,6 +146,11 @@ namespace llvm {<br>
// itself.<br>
const MCSymbol &AliasedSymbol() const;<br>
<br>
+ // If this symbol is not a variable, return itself. If it is a variable,<br>
+ // evaluate it and check if it is of the form Base + ConstantOffset. If so,<br>
+ // return Base, if not, return nullptr.<br>
+ const MCSymbol *getBaseSymbol(const MCAsmLayout &Layout) const;<br>
+<br>
void setVariableValue(const MCExpr *Value);<br>
<br>
/// @}<br>
<br>
Modified: llvm/trunk/lib/MC/ELFObjectWriter.cpp<br>
URL: <a href="http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/MC/ELFObjectWriter.cpp?rev=203962&r1=203961&r2=203962&view=diff" target="_blank">http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/MC/ELFObjectWriter.cpp?rev=203962&r1=203961&r2=203962&view=diff</a><br>
==============================================================================<br>
--- llvm/trunk/lib/MC/ELFObjectWriter.cpp (original)<br>
+++ llvm/trunk/lib/MC/ELFObjectWriter.cpp Fri Mar 14 15:09:04 2014<br>
@@ -271,6 +271,7 @@ class ELFObjectWriter : public MCObjectW<br>
/// \param RevGroupMap - Maps a signature symbol to the group section.<br>
/// \param NumRegularSections - Number of non-relocation sections.<br>
void ComputeSymbolTable(MCAssembler &Asm,<br>
+ const MCAsmLayout &Layout,<br>
const SectionIndexMapTy &SectionIndexMap,<br>
RevGroupMapTy RevGroupMap,<br>
unsigned NumRegularSections);<br>
@@ -462,33 +463,43 @@ void ELFObjectWriter::WriteSymbolEntry(M<br>
}<br>
}<br>
<br>
-uint64_t ELFObjectWriter::SymbolValue(MCSymbolData &Data,<br>
+uint64_t ELFObjectWriter::SymbolValue(MCSymbolData &OrigData,<br>
const MCAsmLayout &Layout) {<br>
- if (Data.isCommon() && Data.isExternal())<br>
- return Data.getCommonAlignment();<br>
-<br>
- const MCSymbol &Symbol = Data.getSymbol();<br>
+ MCSymbolData *Data = &OrigData;<br>
+ if (Data->isCommon() && Data->isExternal())<br>
+ return Data->getCommonAlignment();<br>
+<br>
+ const MCSymbol *Symbol = &Data->getSymbol();<br>
+<br>
+ uint64_t Res = 0;<br>
+ if (Symbol->isVariable()) {<br>
+ const MCExpr *Expr = Symbol->getVariableValue();<br>
+ MCValue Value;<br>
+ if (!Expr->EvaluateAsRelocatable(Value, &Layout))<br>
+ return 0;<br>
+ if (Value.getSymB())<br>
+ return 0;<br>
+ Res = Value.getConstant();<br>
+<br>
+ const MCSymbolRefExpr *A = Value.getSymA();<br>
+ if (!A)<br>
+ return Res;<br>
<br>
- if (Symbol.isAbsolute() && Symbol.isVariable()) {<br>
- if (const MCExpr *Value = Symbol.getVariableValue()) {<br>
- int64_t IntValue;<br>
- if (Value->EvaluateAsAbsolute(IntValue, Layout))<br>
- return (uint64_t)IntValue;<br>
- }<br>
+ Symbol = &A->getSymbol();<br>
+ Data = &Layout.getAssembler().getSymbolData(*Symbol);<br>
}<br>
<br>
- if (!Symbol.isInSection())<br>
+ if (!Symbol->isInSection())<br>
return 0;<br>
<br>
+ if (!Data->getFragment())<br>
+ return 0;<br>
<br>
- if (Data.getFragment()) {<br>
- if (Data.getFlags() & ELF_Other_ThumbFunc)<br>
- return Layout.getSymbolOffset(&Data)+1;<br>
- else<br>
- return Layout.getSymbolOffset(&Data);<br>
- }<br>
+ Res += Layout.getSymbolOffset(Data);<br>
+ if (Data->getFlags() & ELF_Other_ThumbFunc)<br>
+ ++Res;<br>
<br>
- return 0;<br>
+ return Res;<br>
}<br>
<br>
void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm,<br>
@@ -586,7 +597,7 @@ void ELFObjectWriter::WriteSymbol(MCData<br>
uint8_t Other = MCELF::getOther(OrigData) << (ELF_STO_Shift - ELF_STV_Shift);<br>
Other |= Visibility;<br>
<br>
- uint64_t Value = SymbolValue(Data, Layout);<br>
+ uint64_t Value = SymbolValue(OrigData, Layout);<br>
uint64_t Size = 0;<br>
<br>
assert(!(Data.isCommon() && !Data.isExternal()));<br>
@@ -897,10 +908,11 @@ void ELFObjectWriter::ComputeIndexMap(MC<br>
}<br>
}<br>
<br>
-void ELFObjectWriter::ComputeSymbolTable(MCAssembler &Asm,<br>
- const SectionIndexMapTy &SectionIndexMap,<br>
- RevGroupMapTy RevGroupMap,<br>
- unsigned NumRegularSections) {<br>
+void<br>
+ELFObjectWriter::ComputeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,<br>
+ const SectionIndexMapTy &SectionIndexMap,<br>
+ RevGroupMapTy RevGroupMap,<br>
+ unsigned NumRegularSections) {<br>
// FIXME: Is this the correct place to do this?<br>
// FIXME: Why is an undefined reference to _GLOBAL_OFFSET_TABLE_ needed?<br>
if (NeedsGOT) {<br>
@@ -948,33 +960,33 @@ void ELFObjectWriter::ComputeSymbolTable<br>
<br>
ELFSymbolData MSD;<br>
MSD.SymbolData = it;<br>
- const MCSymbol &RefSymbol = Symbol.AliasedSymbol();<br>
+ const MCSymbol *BaseSymbol = Symbol.getBaseSymbol(Layout);<br>
<br>
// Undefined symbols are global, but this is the first place we<br>
// are able to set it.<br>
bool Local = isLocal(*it, isSignature, Used);<br>
if (!Local && MCELF::GetBinding(*it) == ELF::STB_LOCAL) {<br>
- MCSymbolData &SD = Asm.getSymbolData(RefSymbol);<br>
+ assert(BaseSymbol);<br>
+ MCSymbolData &SD = Asm.getSymbolData(*BaseSymbol);<br>
MCELF::SetBinding(*it, ELF::STB_GLOBAL);<br>
MCELF::SetBinding(SD, ELF::STB_GLOBAL);<br>
}<br>
<br>
- if (RefSymbol.isUndefined() && !Used && WeakrefUsed)<br>
- MCELF::SetBinding(*it, ELF::STB_WEAK);<br>
-<br>
- if (it->isCommon()) {<br>
+ if (!BaseSymbol) {<br>
+ MSD.SectionIndex = ELF::SHN_ABS;<br>
+ } else if (it->isCommon()) {<br>
assert(!Local);<br>
MSD.SectionIndex = ELF::SHN_COMMON;<br>
- } else if (Symbol.isAbsolute() || RefSymbol.isVariable()) {<br>
- MSD.SectionIndex = ELF::SHN_ABS;<br>
- } else if (RefSymbol.isUndefined()) {<br>
+ } else if (BaseSymbol->isUndefined()) {<br>
if (isSignature && !Used)<br>
MSD.SectionIndex = SectionIndexMap.lookup(RevGroupMap[&Symbol]);<br>
else<br>
MSD.SectionIndex = ELF::SHN_UNDEF;<br>
+ if (!Used && WeakrefUsed)<br>
+ MCELF::SetBinding(*it, ELF::STB_WEAK);<br>
} else {<br>
const MCSectionELF &Section =<br>
- static_cast<const MCSectionELF&>(RefSymbol.getSection());<br>
+ static_cast<const MCSectionELF&>(BaseSymbol->getSection());<br>
MSD.SectionIndex = SectionIndexMap.lookup(&Section);<br>
if (MSD.SectionIndex >= ELF::SHN_LORESERVE)<br>
NeedsSymtabShndx = true;<br>
@@ -1560,8 +1572,8 @@ void ELFObjectWriter::WriteObject(MCAsse<br>
unsigned NumRegularSections = NumUserSections + NumIndexedSections;<br>
<br>
// Compute symbol table information.<br>
- ComputeSymbolTable(Asm, SectionIndexMap, RevGroupMap, NumRegularSections);<br>
-<br>
+ ComputeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap,<br>
+ NumRegularSections);<br>
<br>
WriteRelocations(Asm, const_cast<MCAsmLayout&>(Layout), RelMap);<br>
<br>
<br>
Modified: llvm/trunk/lib/MC/MCSymbol.cpp<br>
URL: <a href="http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/MC/MCSymbol.cpp?rev=203962&r1=203961&r2=203962&view=diff" target="_blank">http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/MC/MCSymbol.cpp?rev=203962&r1=203961&r2=203962&view=diff</a><br>
==============================================================================<br>
--- llvm/trunk/lib/MC/MCSymbol.cpp (original)<br>
+++ llvm/trunk/lib/MC/MCSymbol.cpp Fri Mar 14 15:09:04 2014<br>
@@ -9,6 +9,7 @@<br>
<br>
#include "llvm/MC/MCSymbol.h"<br>
#include "llvm/MC/MCExpr.h"<br>
+#include "llvm/MC/MCValue.h"<br>
#include "llvm/Support/Debug.h"<br>
#include "llvm/Support/raw_ostream.h"<br>
using namespace llvm;<br>
@@ -51,6 +52,22 @@ const MCSymbol &MCSymbol::AliasedSymbol(<br>
return *S;<br>
}<br>
<br>
+const MCSymbol *MCSymbol::getBaseSymbol(const MCAsmLayout &Layout) const {<br>
+ if (!isVariable())<br>
+ return this;<br>
+<br>
+ const MCExpr *Expr = getVariableValue();<br>
+ MCValue Value;<br>
+ if (!Expr->EvaluateAsRelocatable(Value, &Layout))<br>
+ return nullptr;<br>
+<br>
+ if (Value.getSymB())<br>
+ return nullptr;<br>
+ if (const MCSymbolRefExpr *A = Value.getSymA())<br>
+ return &A->getSymbol();<br>
+ return nullptr;<br>
+}<br>
+<br>
void MCSymbol::setVariableValue(const MCExpr *Value) {<br>
assert(!IsUsed && "Cannot set a variable that has already been used.");<br>
assert(Value && "Invalid variable value!");<br>
<br>
Added: llvm/trunk/test/MC/ELF/offset.s<br>
URL: <a href="http://llvm.org/viewvc/llvm-project/llvm/trunk/test/MC/ELF/offset.s?rev=203962&view=auto" target="_blank">http://llvm.org/viewvc/llvm-project/llvm/trunk/test/MC/ELF/offset.s?rev=203962&view=auto</a><br>
==============================================================================<br>
--- llvm/trunk/test/MC/ELF/offset.s (added)<br>
+++ llvm/trunk/test/MC/ELF/offset.s Fri Mar 14 15:09:04 2014<br>
@@ -0,0 +1,58 @@<br>
+// RUN: llvm-mc -filetype=obj -triple x86_64-pc-linux-gnu %s -o - | llvm-readobj -t - | FileCheck %s<br>
+<br>
+// Test that a variable declared with "var = other_var + cst" is in the same<br>
+// section as other_var and its value is the value of other_var + cst.<br>
+<br>
+ .data<br>
+ .globl sym_a<br>
+ .byte 42<br>
+sym_a:<br>
+<br>
+// CHECK: Symbol {<br>
+// CHECK: Name: sym_a<br>
+// CHECK-NEXT: Value: 0x1<br>
+// CHECK-NEXT: Size: 0<br>
+// CHECK-NEXT: Binding: Global<br>
+// CHECK-NEXT: Type: None<br>
+// CHECK-NEXT: Other: 0<br>
+// CHECK-NEXT: Section: .data<br>
+// CHECK-NEXT: }<br>
+<br>
+ .long 42<br>
+ .globl sym_b<br>
+sym_b:<br>
+ .globl sym_c<br>
+sym_c = sym_a<br>
+// CHECK: Symbol {<br>
+// CHECK: Name: sym_c<br>
+// CHECK-NEXT: Value: 0x1<br>
+// CHECK-NEXT: Size: 0<br>
+// CHECK-NEXT: Binding: Global<br>
+// CHECK-NEXT: Type: None<br>
+// CHECK-NEXT: Other: 0<br>
+// CHECK-NEXT: Section: .data<br>
+// CHECK-NEXT: }<br>
+<br>
+ .globl sym_d<br>
+sym_d = sym_a + 1<br>
+// CHECK: Symbol {<br>
+// CHECK: Name: sym_d<br>
+// CHECK-NEXT: Value: 0x2<br>
+// CHECK-NEXT: Size: 0<br>
+// CHECK-NEXT: Binding: Global<br>
+// CHECK-NEXT: Type: None<br>
+// CHECK-NEXT: Other: 0<br>
+// CHECK-NEXT: Section: .data<br>
+// CHECK-NEXT: }<br>
+<br>
+ .globl sym_e<br>
+sym_e = sym_a + (sym_b - sym_a) * 3<br>
+// CHECK: Symbol {<br>
+// CHECK: Name: sym_e<br>
+// CHECK-NEXT: Value: 0xD<br>
+// CHECK-NEXT: Size: 0<br>
+// CHECK-NEXT: Binding: Global<br>
+// CHECK-NEXT: Type: None<br>
+// CHECK-NEXT: Other: 0<br>
+// CHECK-NEXT: Section: .data<br>
+// CHECK-NEXT: }<br><br></blockquote></div></div></div></div></div></blockquote></div>
</div></div>