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[patch] Adjust behavior of FDE cross-section relocs for targets that don't support abs-differences. 

Modern versions of OSX/Darwin's ld (ld64 > 97.17) have an optimisation present that allows the back end to omit relocations (and replace them with an absolute difference) for FDE some text section refs.

This patch allows a backend to opt-in to this behaviour by setting "DwarfFDESymbolsUseAbsDiff".  At present, this is only enabled for modern x86 OSX ports.

test changes by David Fang.

llvm-svn: 198744
This commit is contained in:
Iain Sandoe 2014-01-08 10:22:54 +00:00
parent 44946439e1
commit 618def651b
5 changed files with 70 additions and 7 deletions
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7
llvm/include/llvm/MC/MCAsmInfo.h
View File

@ -292,6 +292,10 @@ namespace llvm {
/// uses relocations for references to other .debug_* sections.
bool DwarfUsesRelocationsAcrossSections;
/// DwarfFDESymbolsUseAbsDiff - true if DWARF FDE symbol reference
/// relocations should be replaced by an absolute difference.
bool DwarfFDESymbolsUseAbsDiff;
/// DwarfRegNumForCFI - True if dwarf register numbers are printed
/// instead of symbolic register names in .cfi_* directives.
bool DwarfRegNumForCFI; // Defaults to false;
@ -513,6 +517,9 @@ namespace llvm {
bool doesDwarfUseRelocationsAcrossSections() const {
return DwarfUsesRelocationsAcrossSections;
}
bool doDwarfFDESymbolsUseAbsDiff() const {
return DwarfFDESymbolsUseAbsDiff;
}
bool useDwarfRegNumForCFI() const {
return DwarfRegNumForCFI;
}

1
llvm/lib/MC/MCAsmInfo.cpp
View File

@ -84,6 +84,7 @@ MCAsmInfo::MCAsmInfo() {
SupportsDebugInformation = false;
ExceptionsType = ExceptionHandling::None;
DwarfUsesRelocationsAcrossSections = true;
DwarfFDESymbolsUseAbsDiff = false;
DwarfRegNumForCFI = false;
NeedsDwarfSectionOffsetDirective = false;
UseParensForSymbolVariant = false;

16
llvm/lib/MC/MCDwarf.cpp
View File

@ -839,8 +839,9 @@ static unsigned getSizeForEncoding(MCStreamer &streamer,
}
}
static void EmitSymbol(MCStreamer &streamer, const MCSymbol &symbol,
unsigned symbolEncoding, const char *comment = 0) {
static void EmitFDESymbol(MCStreamer &streamer, const MCSymbol &symbol,
unsigned symbolEncoding, bool isEH,
const char *comment = 0) {
MCContext &context = streamer.getContext();
const MCAsmInfo *asmInfo = context.getAsmInfo();
const MCExpr *v = asmInfo->getExprForFDESymbol(&symbol,
@ -848,7 +849,10 @@ static void EmitSymbol(MCStreamer &streamer, const MCSymbol &symbol,
streamer);
unsigned size = getSizeForEncoding(streamer, symbolEncoding);
if (streamer.isVerboseAsm() && comment) streamer.AddComment(comment);
streamer.EmitAbsValue(v, size);
if (asmInfo->doDwarfFDESymbolsUseAbsDiff() && isEH)
streamer.EmitAbsValue(v, size);
else
streamer.EmitValue(v, size);
}
static void EmitPersonality(MCStreamer &streamer, const MCSymbol &symbol,
@ -1347,7 +1351,7 @@ MCSymbol *FrameEmitterImpl::EmitFDE(MCStreamer &streamer,
unsigned PCEncoding = IsEH ? MOFI->getFDEEncoding(UsingCFI)
: (unsigned)dwarf::DW_EH_PE_absptr;
unsigned PCSize = getSizeForEncoding(streamer, PCEncoding);
EmitSymbol(streamer, *frame.Begin, PCEncoding, "FDE initial location");
EmitFDESymbol(streamer, *frame.Begin, PCEncoding, IsEH, "FDE initial location");
// PC Range
const MCExpr *Range = MakeStartMinusEndExpr(streamer, *frame.Begin,
@ -1367,8 +1371,8 @@ MCSymbol *FrameEmitterImpl::EmitFDE(MCStreamer &streamer,
// Augmentation Data
if (frame.Lsda)
EmitSymbol(streamer, *frame.Lsda, frame.LsdaEncoding,
"Language Specific Data Area");
EmitFDESymbol(streamer, *frame.Lsda, frame.LsdaEncoding, true,
"Language Specific Data Area");
}
// Call Frame Instructions

5
llvm/lib/Target/X86/MCTargetDesc/X86MCAsmInfo.cpp
View File

@ -71,6 +71,11 @@ X86MCAsmInfoDarwin::X86MCAsmInfoDarwin(const Triple &T) {
// rather than OS version
if (T.isMacOSX() && T.isMacOSXVersionLT(10, 6))
HasWeakDefCanBeHiddenDirective = false;
// FIXME: this should not depend on the target OS version, but on the ld64
// version in use. From at least >= ld64-97.17 (Xcode 3.2.6) the abs-ified
// FDE relocs may be used.
DwarfFDESymbolsUseAbsDiff = T.isMacOSX() && !T.isMacOSXVersionLT(10, 6);
}
X86_64MCAsmInfoDarwin::X86_64MCAsmInfoDarwin(const Triple &Triple)

48
llvm/test/CodeGen/X86/pr10420.ll
View File

@ -1,4 +1,9 @@
; RUN: llc < %s -mtriple=x86_64-apple-macosx -disable-cfi | FileCheck %s
; RUN: llc < %s -mtriple=x86_64-apple-macosx10.7 -disable-cfi | FileCheck --check-prefix=CHECK-64-D11 %s
; RUN: llc < %s -mtriple=x86_64-apple-macosx10.6 -disable-cfi | FileCheck %s
; RUN: llc < %s -mtriple=x86_64-apple-macosx10.5 -disable-cfi | FileCheck --check-prefix=CHECK-64-D89 %s
; RUN: llc < %s -mtriple=i686-apple-macosx10.6 -disable-cfi | FileCheck --check-prefix=CHECK-I686-D10 %s
; RUN: llc < %s -mtriple=i686-apple-macosx10.5 -disable-cfi | FileCheck --check-prefix=CHECK-I686-D89 %s
; RUN: llc < %s -mtriple=i686-apple-macosx10.4 -disable-cfi | FileCheck --check-prefix=CHECK-I686-D89 %s
define private void @foo() {
ret void
@ -19,3 +24,44 @@ define void @bar() {
; CHECK: Ltmp19:
; CHECK-NEXT: Ltmp20 = Ltmp2-Ltmp19 ## FDE initial location
; CHECK-NEXT: .quad Ltmp20
; CHECK-64-D11: Ltmp13:
; CHECK-64-D11-NEXT: Ltmp14 = L_foo-Ltmp13 ## FDE initial location
; CHECK-64-D11-NEXT: .quad Ltmp14
; CHECK-64-D11: Ltmp20:
; CHECK-64-D11-NEXT: Ltmp21 = Ltmp2-Ltmp20 ## FDE initial location
; CHECK-64-D11-NEXT: .quad Ltmp21
; CHECK-64-D89: Ltmp12:
; CHECK-64-D89-NEXT: .quad L_foo-Ltmp12 ## FDE initial location
; CHECK-64-D89-NEXT: Ltmp13 = (Ltmp0-L_foo)-0 ## FDE address range
; CHECK-64-D89-NEXT: .quad Ltmp13
; CHECK-64-D89: Ltmp18:
; CHECK-64-D89-NEXT: .quad Ltmp2-Ltmp18 ## FDE initial location
; CHECK-64-D89-NEXT: Ltmp19 = (Ltmp4-Ltmp2)-0 ## FDE address range
; CHECK-64-D89-NEXT: .quad Ltmp19
; CHECK-I686-D10: Ltmp12:
; CHECK-I686-D10-NEXT: Ltmp13 = L_foo-Ltmp12 ## FDE initial location
; CHECK-I686-D10-NEXT: .long Ltmp13
; CHECK-I686-D10: Ltmp19:
; CHECK-I686-D10-NEXT: Ltmp20 = Ltmp2-Ltmp19 ## FDE initial location
; CHECK-I686-D10-NEXT: .long Ltmp20
; CHECK-I686-D89: Ltmp12:
; CHECK-I686-D89-NEXT: .long L_foo-Ltmp12 ## FDE initial location
; CHECK-I686-D89-NEXT: Ltmp13 = (Ltmp0-L_foo)-0 ## FDE address range
; CHECK-I686-D89-NEXT: .long Ltmp13
; CHECK-I686-D89: Ltmp18:
; CHECK-I686-D89-NEXT: .long Ltmp2-Ltmp18 ## FDE initial location
; CHECK-I686-D89-NEXT: Ltmp19 = (Ltmp4-Ltmp2)-0 ## FDE address range
; CHECK-I686-D89-NEXT: .long Ltmp19