[llvm] r293667 - MC: Introduce the ABS8 symbol modifier.
Peter Collingbourne via llvm-commits
llvm-commits at lists.llvm.org
Tue Jan 31 10:28:44 PST 2017
Author: pcc
Date: Tue Jan 31 12:28:44 2017
New Revision: 293667
URL: http://llvm.org/viewvc/llvm-project?rev=293667&view=rev
Log:
MC: Introduce the ABS8 symbol modifier.
@ABS8 can be applied to symbols which appear as immediate operands to
instructions that have a 8-bit immediate form for that operand. It causes
the assembler to use the 8-bit form and an 8-bit relocation (e.g. R_386_8
or R_X86_64_8) for the symbol.
Differential Revision: https://reviews.llvm.org/D28688
Added:
llvm/trunk/test/MC/X86/abs8.s
Modified:
llvm/trunk/docs/Extensions.rst
llvm/trunk/include/llvm/MC/MCExpr.h
llvm/trunk/lib/MC/MCAssembler.cpp
llvm/trunk/lib/MC/MCExpr.cpp
llvm/trunk/lib/Target/X86/MCTargetDesc/X86ELFObjectWriter.cpp
Modified: llvm/trunk/docs/Extensions.rst
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/Extensions.rst?rev=293667&r1=293666&r2=293667&view=diff
==============================================================================
--- llvm/trunk/docs/Extensions.rst (original)
+++ llvm/trunk/docs/Extensions.rst Tue Jan 31 12:28:44 2017
@@ -207,6 +207,28 @@ in the assembler to differentiate the se
Target Specific Behaviour
=========================
+X86
+---
+
+Relocations
+^^^^^^^^^^^
+
+``@ABS8`` can be applied to symbols which appear as immediate operands to
+instructions that have an 8-bit immediate form for that operand. It causes
+the assembler to use the 8-bit form and an 8-bit relocation (e.g. ``R_386_8``
+or ``R_X86_64_8``) for the symbol.
+
+For example:
+
+.. code-block:: gas
+
+ cmpq $foo at ABS8, %rdi
+
+This causes the assembler to select the form of the 64-bit ``cmpq`` instruction
+that takes an 8-bit immediate operand that is sign extended to 64 bits, as
+opposed to ``cmpq $foo, %rdi`` which takes a 32-bit immediate operand. This
+is also not the same as ``cmpb $foo, %dil``, which is an 8-bit comparison.
+
Windows on ARM
--------------
Modified: llvm/trunk/include/llvm/MC/MCExpr.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/MC/MCExpr.h?rev=293667&r1=293666&r2=293667&view=diff
==============================================================================
--- llvm/trunk/include/llvm/MC/MCExpr.h (original)
+++ llvm/trunk/include/llvm/MC/MCExpr.h Tue Jan 31 12:28:44 2017
@@ -194,6 +194,8 @@ public:
VK_SIZE, // symbol at SIZE
VK_WEAKREF, // The link between the symbols in .weakref foo, bar
+ VK_X86_ABS8,
+
VK_ARM_NONE,
VK_ARM_GOT_PREL,
VK_ARM_TARGET1,
Modified: llvm/trunk/lib/MC/MCAssembler.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/MC/MCAssembler.cpp?rev=293667&r1=293666&r2=293667&view=diff
==============================================================================
--- llvm/trunk/lib/MC/MCAssembler.cpp (original)
+++ llvm/trunk/lib/MC/MCAssembler.cpp Tue Jan 31 12:28:44 2017
@@ -747,6 +747,10 @@ bool MCAssembler::fixupNeedsRelaxation(c
MCValue Target;
uint64_t Value;
bool Resolved = evaluateFixup(Layout, Fixup, DF, Target, Value);
+ if (Target.getSymA() &&
+ Target.getSymA()->getKind() == MCSymbolRefExpr::VK_X86_ABS8 &&
+ Fixup.getKind() == FK_Data_1)
+ return false;
return getBackend().fixupNeedsRelaxationAdvanced(Fixup, Resolved, Value, DF,
Layout);
}
Modified: llvm/trunk/lib/MC/MCExpr.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/MC/MCExpr.cpp?rev=293667&r1=293666&r2=293667&view=diff
==============================================================================
--- llvm/trunk/lib/MC/MCExpr.cpp (original)
+++ llvm/trunk/lib/MC/MCExpr.cpp Tue Jan 31 12:28:44 2017
@@ -208,6 +208,7 @@ StringRef MCSymbolRefExpr::getVariantKin
case VK_SECREL: return "SECREL32";
case VK_SIZE: return "SIZE";
case VK_WEAKREF: return "WEAKREF";
+ case VK_X86_ABS8: return "ABS8";
case VK_ARM_NONE: return "none";
case VK_ARM_GOT_PREL: return "GOT_PREL";
case VK_ARM_TARGET1: return "target1";
@@ -317,6 +318,7 @@ MCSymbolRefExpr::getVariantKindForName(S
.Case("imgrel", VK_COFF_IMGREL32)
.Case("secrel32", VK_SECREL)
.Case("size", VK_SIZE)
+ .Case("abs8", VK_X86_ABS8)
.Case("l", VK_PPC_LO)
.Case("h", VK_PPC_HI)
.Case("ha", VK_PPC_HA)
Modified: llvm/trunk/lib/Target/X86/MCTargetDesc/X86ELFObjectWriter.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/MCTargetDesc/X86ELFObjectWriter.cpp?rev=293667&r1=293666&r2=293667&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/MCTargetDesc/X86ELFObjectWriter.cpp (original)
+++ llvm/trunk/lib/Target/X86/MCTargetDesc/X86ELFObjectWriter.cpp Tue Jan 31 12:28:44 2017
@@ -96,6 +96,7 @@ static unsigned getRelocType64(MCContext
default:
llvm_unreachable("Unimplemented");
case MCSymbolRefExpr::VK_None:
+ case MCSymbolRefExpr::VK_X86_ABS8:
switch (Type) {
case RT64_64:
return IsPCRel ? ELF::R_X86_64_PC64 : ELF::R_X86_64_64;
@@ -219,6 +220,7 @@ static unsigned getRelocType32(MCContext
default:
llvm_unreachable("Unimplemented");
case MCSymbolRefExpr::VK_None:
+ case MCSymbolRefExpr::VK_X86_ABS8:
switch (Type) {
case RT32_32:
return IsPCRel ? ELF::R_386_PC32 : ELF::R_386_32;
Added: llvm/trunk/test/MC/X86/abs8.s
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/MC/X86/abs8.s?rev=293667&view=auto
==============================================================================
--- llvm/trunk/test/MC/X86/abs8.s (added)
+++ llvm/trunk/test/MC/X86/abs8.s Tue Jan 31 12:28:44 2017
@@ -0,0 +1,8 @@
+// RUN: llvm-mc -filetype=obj %s -o - -triple i686-pc-linux | llvm-objdump -d -r - | FileCheck --check-prefix=32 %s
+// RUN: llvm-mc -filetype=obj %s -o - -triple x86_64-pc-linux | llvm-objdump -d -r - | FileCheck --check-prefix=64 %s
+
+// 32: 0: 83 ff 00 cmpl $0, %edi
+// 32: 00000002: R_386_8 foo
+// 64: 0: 83 ff 00 cmpl $0, %edi
+// 64: 0000000000000002: R_X86_64_8 foo+0
+cmp $foo at ABS8, %edi
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