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[MC] [Win64EH] Fix the calculation of the end of epilogs 

Exclude the terminating end opcode from the epilog - it doesn't
correspond to an actual instruction that is included in the epilog
itself (within the .seh_startepilogue/.seh_endepilogue range).

In most (all?) cases, an epilog is followed by a matching terminating
instruction though (a ret or a branch to a tail call), but it's not
strictly within the .seh_startepilogue/.seh_endepilogue range.

This fixes a number of failed asserts in cases where the codegen
has incorrectly reoredered SEH opcodes so they don't match up
exactly with their instructions.

However this still just avoids failing the assertion; the root cause
of generating unexpected epilogs is still present (and fixing that is
a less obvious issue).

Differential Revision: https://reviews.llvm.org/D131393
This commit is contained in:
Martin Storsjö 2022-08-08 12:34:29 +03:00
parent f181dff084
commit 0c52ab3968
2 changed files with 65 additions and 1 deletions
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4
llvm/lib/MC/MCWin64EH.cpp
View File

@ -997,7 +997,9 @@ static void ARM64FindSegmentsInFunction(MCStreamer &streamer,
int64_t Offset = GetAbsDifference(streamer, Start, info->Begin);
assert((Epilogs.size() == 0 || Offset >= Epilogs.back().End) &&
"Epilogs should be monotonically ordered");
Epilogs.push_back({Start, Offset, Offset + (int64_t)Instrs.size() * 4});
// Exclue the end opcode from Instrs.size() when calculating the end of the
// epilog.
Epilogs.push_back({Start, Offset, Offset + (int64_t)(Instrs.size() - 1) * 4});
}
unsigned E = 0;

62
llvm/test/MC/AArch64/seh-multi-epilog.s Normal file
View File

@ -0,0 +1,62 @@
// This test checks that we emit allow multiple consecutive epilogs without
// triggering failed asserts.unwind info correctly for epilogs that:
// RUN: llvm-mc -triple aarch64-pc-win32 -filetype=obj %s -o %t.o
// RUN: llvm-readobj -u %t.o | FileCheck %s
// CHECK-LABEL:UnwindInformation [
// CHECK-NEXT: RuntimeFunction {
// CHECK-NEXT: Function: multi_epilog (0x0)
// CHECK-NEXT: ExceptionRecord: .xdata (0x0)
// CHECK-NEXT: ExceptionData {
// CHECK-NEXT: FunctionLength: 20
// CHECK-NEXT: Version: 0
// CHECK-NEXT: ExceptionData: No
// CHECK-NEXT: EpiloguePacked: No
// CHECK-NEXT: EpilogueScopes: 2
// CHECK-NEXT: ByteCodeLength: 4
// CHECK-NEXT: Prologue [
// CHECK-NEXT: 0x81 ; stp x29, x30, [sp, #-16]!
// CHECK-NEXT: 0xe4 ; end
// CHECK-NEXT: ]
// CHECK-NEXT: EpilogueScopes [
// CHECK-NEXT: EpilogueScope {
// CHECK-NEXT: StartOffset: 2
// CHECK-NEXT: EpilogueStartIndex: 0
// CHECK-NEXT: Opcodes [
// CHECK-NEXT: 0x81 ; ldp x29, x30, [sp], #16
// CHECK-NEXT: 0xe4 ; end
// CHECK-NEXT: ]
// CHECK-NEXT: }
// CHECK-NEXT: EpilogueScope {
// CHECK-NEXT: StartOffset: 3
// CHECK-NEXT: EpilogueStartIndex: 0
// CHECK-NEXT: Opcodes [
// CHECK-NEXT: 0x81 ; ldp x29, x30, [sp], #16
// CHECK-NEXT: 0xe4 ; end
// CHECK-NEXT: ]
// CHECK-NEXT: }
// CHECK-NEXT: ]
// CHECK-NEXT: }
// CHECK-NEXT: }
// CHECK-NEXT:]
.text
.global multi_epilog
.p2align 2
.seh_proc multi_epilog
multi_epilog:
stp x29, lr, [sp, #-16]!
.seh_save_fplr_x 16
.seh_endprologue
nop
.seh_startepilogue
ldp x29, lr, [sp], #16
.seh_save_fplr_x 16
.seh_endepilogue
.seh_startepilogue
ldp x29, lr, [sp], #16
.seh_save_fplr_x 16
.seh_endepilogue
ret
.seh_endfunclet
.seh_endproc