[llvm] 2d8c18f - [X86] Don't add implicit REP prefix to VIA PadLock xstore

[Jessica Clarke via llvm-commits]

Author: Jessica Clarke
Date: 2021-10-23T01:57:17+01:00
New Revision: 2d8c18fbbdd1b07ab0d36ac49ef63f4d243afb8b

URL: https://github.com/llvm/llvm-project/commit/2d8c18fbbdd1b07ab0d36ac49ef63f4d243afb8b
DIFF: https://github.com/llvm/llvm-project/commit/2d8c18fbbdd1b07ab0d36ac49ef63f4d243afb8b.diff

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

Commit 8fa3e8fa1492 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

Added: 
    

Modified: 
    llvm/lib/Target/X86/X86InstrSystem.td
    llvm/test/MC/X86/padlock.s

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Target/X86/X86InstrSystem.td b/llvm/lib/Target/X86/X86InstrSystem.td
index 0f86f0364ccd1..b4dd99d08a626 100644
--- a/llvm/lib/Target/X86/X86InstrSystem.td
+++ b/llvm/lib/Target/X86/X86InstrSystem.td
@@ -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)>;
 

diff  --git a/llvm/test/MC/X86/padlock.s b/llvm/test/MC/X86/padlock.s
index c79d346fa23ee..9f9b16294ea02 100644
--- a/llvm/test/MC/X86/padlock.s
+++ b/llvm/test/MC/X86/padlock.s
@@ -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]