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[X86] Don't add implicit REP prefix to VIA PadLock xstore 

Commit 8fa3e8fa14 added an implicit REP prefix to all VIA PadLock
instructions, but GNU as doesn't add one to xstore, only all the others.
This resulted in a kernel panic regression in FreeBSD upon updating to
LLVM 11 (https://bugs.freebsd.org/259218) which includes the commit in
question. This partially reverts that commit.

Reviewed By: craig.topper

Differential Revision: https://reviews.llvm.org/D112355
This commit is contained in:
Jessica Clarke 2021-10-23 01:56:05 +01:00
parent b432583d28
commit 2d8c18fbbd
2 changed files with 5 additions and 2 deletions
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2
llvm/lib/Target/X86/X86InstrSystem.td
View File

@ -584,7 +584,7 @@ def XRSTORS64 : RI<0xC7, MRM3m, (outs), (ins opaquemem:$dst),
//===----------------------------------------------------------------------===//
// VIA PadLock crypto instructions
let Defs = [RAX, RDI], Uses = [RDX, RDI], SchedRW = [WriteSystem] in
def XSTORE : I<0xa7, MRM_C0, (outs), (ins), "xstore", []>, TB, REP;
def XSTORE : I<0xa7, MRM_C0, (outs), (ins), "xstore", []>, TB;
def : InstAlias<"xstorerng", (XSTORE)>;

5
llvm/test/MC/X86/padlock.s
View File

@ -1,8 +1,11 @@
// RUN: llvm-mc -triple i386-unknown-unknown --show-encoding %s | FileCheck %s
/// Check xstore does not get an implicit REP prefix but all other PadLock
/// instructions do.
xstore
// CHECK: xstore
// CHECK: encoding: [0xf3,0x0f,0xa7,0xc0]
// CHECK: encoding: [0x0f,0xa7,0xc0]
xcryptecb
// CHECK: xcryptecb
// CHECK: encoding: [0xf3,0x0f,0xa7,0xc8]