[llvm-commits] [llvm] r164724 - in /llvm/trunk: lib/Target/X86/MCTargetDesc/X86MachObjectWriter.cpp test/MC/MachO/i386-large-relocations.s
Jim Grosbach
grosbach at apple.com
Wed Sep 26 14:27:45 PDT 2012
Author: grosbach
Date: Wed Sep 26 16:27:45 2012
New Revision: 164724
URL: http://llvm.org/viewvc/llvm-project?rev=164724&view=rev
Log:
X86_32: Large Symbol+Offset relocations.
If the offset is more than 24-bits, it won't fit in a scattered
relocation offset field, so we fall back to using a non-scattered
relocation.
rdar://12358909
Added:
llvm/trunk/test/MC/MachO/i386-large-relocations.s
Modified:
llvm/trunk/lib/Target/X86/MCTargetDesc/X86MachObjectWriter.cpp
Modified: llvm/trunk/lib/Target/X86/MCTargetDesc/X86MachObjectWriter.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/MCTargetDesc/X86MachObjectWriter.cpp?rev=164724&r1=164723&r2=164724&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/MCTargetDesc/X86MachObjectWriter.cpp (original)
+++ llvm/trunk/lib/Target/X86/MCTargetDesc/X86MachObjectWriter.cpp Wed Sep 26 16:27:45 2012
@@ -11,11 +11,13 @@
#include "MCTargetDesc/X86MCTargetDesc.h"
#include "llvm/MC/MCAssembler.h"
#include "llvm/MC/MCAsmLayout.h"
+#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCMachObjectWriter.h"
#include "llvm/MC/MCSectionMachO.h"
#include "llvm/MC/MCValue.h"
#include "llvm/ADT/Twine.h"
#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/Format.h"
#include "llvm/Object/MachOFormat.h"
using namespace llvm;
@@ -23,7 +25,7 @@
namespace {
class X86MachObjectWriter : public MCMachObjectTargetWriter {
- void RecordScatteredRelocation(MachObjectWriter *Writer,
+ bool RecordScatteredRelocation(MachObjectWriter *Writer,
const MCAssembler &Asm,
const MCAsmLayout &Layout,
const MCFragment *Fragment,
@@ -335,7 +337,7 @@
Writer->addRelocation(Fragment->getParent(), MRE);
}
-void X86MachObjectWriter::RecordScatteredRelocation(MachObjectWriter *Writer,
+bool X86MachObjectWriter::RecordScatteredRelocation(MachObjectWriter *Writer,
const MCAssembler &Asm,
const MCAsmLayout &Layout,
const MCFragment *Fragment,
@@ -381,6 +383,19 @@
// Relocations are written out in reverse order, so the PAIR comes first.
if (Type == macho::RIT_Difference ||
Type == macho::RIT_Generic_LocalDifference) {
+ // If the offset is too large to fit in a scattered relocation,
+ // we're hosed. It's an unfortunate limitation of the MachO format.
+ if (FixupOffset > 0xffffff) {
+ char Buffer[32];
+ format("0x%x", FixupOffset).print(Buffer, sizeof(Buffer));
+ Asm.getContext().FatalError(Fixup.getLoc(),
+ Twine("Section too large, can't encode "
+ "r_address (") + Buffer +
+ ") into 24 bits of scattered "
+ "relocation entry.");
+ llvm_unreachable("fatal error returned?!");
+ }
+
macho::RelocationEntry MRE;
MRE.Word0 = ((0 << 0) |
(macho::RIT_Pair << 24) |
@@ -389,6 +404,16 @@
macho::RF_Scattered);
MRE.Word1 = Value2;
Writer->addRelocation(Fragment->getParent(), MRE);
+ } else {
+ // If the offset is more than 24-bits, it won't fit in a scattered
+ // relocation offset field, so we fall back to using a non-scattered
+ // relocation. This is a bit risky, as if the offset reaches out of
+ // the block and the linker is doing scattered loading on this
+ // symbol, things can go badly.
+ //
+ // Required for 'as' compatibility.
+ if (FixupOffset > 0xffffff)
+ return false;
}
macho::RelocationEntry MRE;
@@ -399,6 +424,7 @@
macho::RF_Scattered);
MRE.Word1 = Value;
Writer->addRelocation(Fragment->getParent(), MRE);
+ return true;
}
void X86MachObjectWriter::RecordTLVPRelocation(MachObjectWriter *Writer,
@@ -469,9 +495,11 @@
// If this is a difference or a defined symbol plus an offset, then we need a
// scattered relocation entry. Differences always require scattered
// relocations.
- if (Target.getSymB())
- return RecordScatteredRelocation(Writer, Asm, Layout, Fragment, Fixup,
- Target, Log2Size, FixedValue);
+ if (Target.getSymB()) {
+ RecordScatteredRelocation(Writer, Asm, Layout, Fragment, Fixup,
+ Target, Log2Size, FixedValue);
+ return;
+ }
// Get the symbol data, if any.
MCSymbolData *SD = 0;
@@ -483,9 +511,13 @@
uint32_t Offset = Target.getConstant();
if (IsPCRel)
Offset += 1 << Log2Size;
- if (Offset && SD && !Writer->doesSymbolRequireExternRelocation(SD))
- return RecordScatteredRelocation(Writer, Asm, Layout, Fragment, Fixup,
- Target, Log2Size, FixedValue);
+ // Try to record the scattered relocation if needed. Fall back to non
+ // scattered if necessary (see comments in RecordScatteredRelocation()
+ // for details).
+ if (Offset && SD && !Writer->doesSymbolRequireExternRelocation(SD) &&
+ RecordScatteredRelocation(Writer, Asm, Layout, Fragment, Fixup,
+ Target, Log2Size, FixedValue))
+ return;
// See <reloc.h>.
uint32_t FixupOffset = Layout.getFragmentOffset(Fragment)+Fixup.getOffset();
Added: llvm/trunk/test/MC/MachO/i386-large-relocations.s
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/MC/MachO/i386-large-relocations.s?rev=164724&view=auto
==============================================================================
--- llvm/trunk/test/MC/MachO/i386-large-relocations.s (added)
+++ llvm/trunk/test/MC/MachO/i386-large-relocations.s Wed Sep 26 16:27:45 2012
@@ -0,0 +1,36 @@
+// RUN: llvm-mc -triple i386-apple-darwin10 %s -filetype=obj -o - | macho-dump | FileCheck %s
+
+.space 0x1ed280
+ .section __DATA,__const
+ .align 4
+.space 0x5181020
+_foo:
+ .long _bar
+ .long 0
+ .long _bar+8
+ .long _bar+24
+ .long 0
+ .long _bar+16
+
+.zerofill __DATA,__bss,__dummy,0x5d780
+.zerofill __DATA,__bss,_bar,48,4
+
+// Normally scattered relocations are used for sym+offset expressions. When
+// the value exceeds 24-bits, however, it's outside what MachO can encode,
+// so the assembler falls back to non-scattered relocations.
+// rdar://12358909
+
+// CHECK: ('_relocations', [
+// CHECK: # Relocation 0
+// CHECK: (('word-0', 0x5181034),
+// CHECK: ('word-1', 0x4000003)),
+// CHECK: # Relocation 1
+// CHECK: (('word-0', 0x518102c),
+// CHECK: ('word-1', 0x4000003)),
+// CHECK: # Relocation 2
+// CHECK: (('word-0', 0x5181028),
+// CHECK: ('word-1', 0x4000003)),
+// CHECK: # Relocation 3
+// CHECK: (('word-0', 0x5181020),
+// CHECK: ('word-1', 0x4000003)),
+// CHECK: ])
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