[PATCH] D121017: [AArch64] Fallback to DWARF when trying to emit compact unwind info with multiple CFA offset adjustments

[Momchil Velikov via Phabricator via llvm-commits]

chill created this revision.
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Instead of asserting, fallback to emitting DWARF unwind info when an
attempt is made to output compact unwind info for a function with
multiple adjustments to the CFA offset.

Multiple adjustments of SP are common and with instruction precise
unwind tables these may translate into multiple `.cfi_def_cfa_offset`
directives.

      

Fixes https://bugs.chromium.org/p/chromium/issues/detail?id=1302998


https://reviews.llvm.org/D121017

Files:
  llvm/lib/Target/AArch64/MCTargetDesc/AArch64AsmBackend.cpp
  llvm/test/MC/AArch64/arm64-compact-unwind-fallback.s


Index: llvm/test/MC/AArch64/arm64-compact-unwind-fallback.s
===================================================================
--- llvm/test/MC/AArch64/arm64-compact-unwind-fallback.s
+++ llvm/test/MC/AArch64/arm64-compact-unwind-fallback.s
@@ -5,11 +5,21 @@
 
 // CHECK: Contents of __compact_unwind section:
 // CHECK: compact encoding:     0x03000000
+// CHECK: compact encoding:     0x03000000
 
 // CHECK: .eh_frame contents:
 // CHECK: DW_CFA_def_cfa: reg1 +32
 
-_cfi_dwarf:
+//  DW_CFA_def_cfa_offset: +32
+//  DW_CFA_def_cfa_offset: +64
+
+_cfi_dwarf0:
  .cfi_startproc
  .cfi_def_cfa x1, 32;
  .cfi_endproc
+
+_cfi_dwarf1:
+ .cfi_startproc
+ .cfi_def_cfa_offset 32
+ .cfi_def_cfa_offset 64
+ .cfi_endproc
Index: llvm/lib/Target/AArch64/MCTargetDesc/AArch64AsmBackend.cpp
===================================================================
--- llvm/lib/Target/AArch64/MCTargetDesc/AArch64AsmBackend.cpp
+++ llvm/lib/Target/AArch64/MCTargetDesc/AArch64AsmBackend.cpp
@@ -621,7 +621,8 @@
         break;
       }
       case MCCFIInstruction::OpDefCfaOffset: {
-        assert(StackSize == 0 && "We already have the CFA offset!");
+        if (StackSize != 0)
+          return CU::UNWIND_ARM64_MODE_DWARF;
         StackSize = std::abs(Inst.getOffset());
         break;
       }


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