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[X86] Support function attribute "patchable-function-entry"

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For x86-64, we diverge from GCC -fpatchable-function-entry in that we
emit multi-byte NOPs.

Differential Revision: https://reviews.llvm.org/D72220
This commit is contained in:
Fangrui Song 2020-01-04 19:52:36 -08:00
parent 4d1e23e3b3
commit a8fbdc5769
2 changed files with 73 additions and 3 deletions
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18
llvm/lib/Target/X86/X86MCInstLower.cpp
View File

@ -1035,9 +1035,11 @@ void X86AsmPrinter::LowerTlsAddr(X86MCInstLower &MCInstLowering,
/// bytes. Return the size of nop emitted.
static unsigned EmitNop(MCStreamer &OS, unsigned NumBytes, bool Is64Bit,
const MCSubtargetInfo &STI) {
// This works only for 64bit. For 32bit we have to do additional checking if
// the CPU supports multi-byte nops.
assert(Is64Bit && "EmitNops only supports X86-64");
if (!Is64Bit) {
// TODO Do additional checking if the CPU supports multi-byte nops.
OS.EmitInstruction(MCInstBuilder(X86::NOOP), STI);
return 1;
}
unsigned NopSize;
unsigned Opc, BaseReg, ScaleVal, IndexReg, Displacement, SegmentReg;
@ -1597,6 +1599,16 @@ void X86AsmPrinter::LowerPATCHABLE_FUNCTION_ENTER(const MachineInstr &MI,
NoAutoPaddingScope NoPadScope(*OutStreamer);
const Function &F = MF->getFunction();
if (F.hasFnAttribute("patchable-function-entry")) {
unsigned Num;
if (F.getFnAttribute("patchable-function-entry")
.getValueAsString()
.getAsInteger(10, Num))
return;
EmitNops(*OutStreamer, Num, Subtarget->is64Bit(), getSubtargetInfo());
return;
}
// We want to emit the following pattern:
//
// .p2align 1, ...

58
llvm/test/CodeGen/X86/patchable-function-entry.ll Normal file
View File

@ -0,0 +1,58 @@
; RUN: llc -mtriple=i386 %s -o - | FileCheck --check-prefixes=CHECK,NOFSECT,32 %s
; RUN: llc -mtriple=x86_64 %s -o - | FileCheck --check-prefixes=CHECK,NOFSECT,64 %s
define void @f0() "patchable-function-entry"="0" {
; CHECK-LABEL: f0:
; CHECK-NEXT: .Lfunc_begin0:
; CHECK-NOT: nop
; CHECK: ret
; CHECK: .section __patchable_function_entries,"awo",@progbits,f0,unique,0
; 32: .p2align 2
; 32-NEXT: .long .Lfunc_begin0
; 64: .p2align 3
; 64-NEXT: .quad .Lfunc_begin0
ret void
}
define void @f1() "patchable-function-entry"="1" {
; CHECK-LABEL: f1:
; CHECK: nop
; CHECK-NEXT: ret
; NOFSECT: .section __patchable_function_entries,"awo",@progbits,f0,unique,0
; FSECT: .section __patchable_function_entries,"awo",@progbits,f1,unique,1
; 32: .p2align 2
; 32-NEXT: .long .Lfunc_begin1
; 64: .p2align 3
; 64-NEXT: .quad .Lfunc_begin1
ret void
}
$f3 = comdat any
define void @f3() "patchable-function-entry"="3" comdat {
; CHECK-LABEL: f3:
; 32-COUNT-3: nop
; 64: nopl (%rax)
; CHECK: ret
; NOFSECT: .section __patchable_function_entries,"aGwo",@progbits,f3,comdat,f3,unique,1
; FSECT: .section __patchable_function_entries,"aGwo",@progbits,f3,comdat,f3,unique,2
; 32: .p2align 2
; 32-NEXT: .long .Lfunc_begin2
; 64: .p2align 3
; 64-NEXT: .quad .Lfunc_begin2
ret void
}
$f5 = comdat any
define void @f5() "patchable-function-entry"="5" comdat {
; CHECK-LABEL: f5:
; 32-COUNT-5: nop
; 64: nopl 8(%rax,%rax)
; CHECK-NEXT: ret
; NOFSECT .section __patchable_function_entries,"aGwo",@progbits,f5,comdat,f5,unique,2
; FSECT: .section __patchable_function_entries,"aGwo",@progbits,f5,comdat,f5,unique,3
; 32: .p2align 2
; 32-NEXT: .long .Lfunc_begin3
; 64: .p2align 3
; 64-NEXT: .quad .Lfunc_begin3
ret void
}