[LoongArch] Set correct encodings for DWARF exception handling

[wangleiat]

Summary

This patch sets correct encodings for DWARF exception handling for
LoongArch.

Depends on D134709

[xen0n]

LGTM but I haven't cross-checked with gcc.

llvm/test/CodeGen/LoongArch/dwarf-eh.ll

4

nit: one single space

[xry111]

In D134710#3819859, @xen0n wrote:

LGTM but I haven't cross-checked with gcc.

https://gcc.gnu.org/git?p=gcc.git;a=blob;f=gcc/config/loongarch/loongarch.h#l1133:

#ifdef HAVE_AS_EH_FRAME_PCREL_ENCODING_SUPPORT
#define ASM_PREFERRED_EH_DATA_FORMAT(CODE, GLOBAL) \
  (((GLOBAL) ? DW_EH_PE_indirect : 0) | DW_EH_PE_pcrel | DW_EH_PE_sdata4)
#else
#define ASM_PREFERRED_EH_DATA_FORMAT(CODE, GLOBAL) \
  (((GLOBAL) ? DW_EH_PE_indirect : 0) | DW_EH_PE_absptr)
#endif

The ifdef is just for old GNU assemblers, we don't need to care about it because normally LLVM doesn't use an external assembler. I'm not sure about the difference with DW_EH_PE_indirect though (I know literally, nothing about debug symbols).

[wangleiat]

In D134710#3819861, @xry111 wrote:

In D134710#3819859, @xen0n wrote:

LGTM but I haven't cross-checked with gcc.

https://gcc.gnu.org/git?p=gcc.git;a=blob;f=gcc/config/loongarch/loongarch.h#l1133:

#ifdef HAVE_AS_EH_FRAME_PCREL_ENCODING_SUPPORT
#define ASM_PREFERRED_EH_DATA_FORMAT(CODE, GLOBAL) \
  (((GLOBAL) ? DW_EH_PE_indirect : 0) | DW_EH_PE_pcrel | DW_EH_PE_sdata4)
#else
#define ASM_PREFERRED_EH_DATA_FORMAT(CODE, GLOBAL) \
  (((GLOBAL) ? DW_EH_PE_indirect : 0) | DW_EH_PE_absptr)
#endif

The ifdef is just for old GNU assemblers, we don't need to care about it because normally LLVM doesn't use an external assembler.

Considering that the old binutils might be used, gcc keeps this definition:

#define ASM_PREFERRED_EH_DATA_FORMAT(CODE, GLOBAL) \
  (((GLOBAL) ? DW_EH_PE_indirect : 0) | DW_EH_PE_absptr)

I'm not sure about the difference with DW_EH_PE_indirect though (I know literally, nothing about debug symbols).

The definition here is simply to keep consistent with gcc. As for DW_EH_PE_indirect, it seems to be for the read-only attribute of .eh_frame section.

llvm/test/CodeGen/LoongArch/dwarf-eh.ll

4

nit: one single space

Thanks, I will remove the extra spaces.

[wangleiat]

Address @xen0n's comments

[xen0n]

Cross-checked with some gcc code and it looks okay. I don't think we should care for old binutils, the new-world userbase is small enough it'd be easier to tell everyone to upgrade than maintaining such a compatibility hack indefinitely.

[MaskRay]

One nit

llvm/test/CodeGen/LoongArch/dwarf-eh.ll

2

Better to set --relocation-model=static instead of relying on the default.

[wangleiat]

llvm/test/CodeGen/LoongArch/dwarf-eh.ll

2

Better to set --relocation-model=static instead of relying on the default.

Thanks, I will modify it.

[wangleiat]

Address @MaskRay's comment.

llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp

if (isPositionIndependent()) {
       TTypeEncoding = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
         dwarf::DW_EH_PE_sdata4;
     } else {
       PersonalityEncoding = dwarf::DW_EH_PE_absptr;
       LSDAEncoding = dwarf::DW_EH_PE_absptr;
       TTypeEncoding = dwarf::DW_EH_PE_absptr;
     }
     break;
+  case Triple::loongarch32:
+  case Triple::loongarch64:
+    LSDAEncoding = dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4;
+    PersonalityEncoding = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
+                          dwarf::DW_EH_PE_sdata4;
+    TTypeEncoding = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
+                    dwarf::DW_EH_PE_sdata4;
+    break;
   default:
     break;
   }
 }
 
 void TargetLoweringObjectFileELF::getModuleMetadata(Module &M) {
   SmallVector<GlobalValue *, 4> Vec;
   collectUsedGlobalVariables(M, Vec, false);

llvm/test/CodeGen/LoongArch/dwarf-eh.ll

+; RUN: llc --mtriple=loongarch32  < %s | FileCheck %s
+; RUN: llc --mtriple=loongarch32  --relocation-model=pic < %s | FileCheck %s
+; RUN: llc --mtriple=loongarch64  < %s | FileCheck %s
+; RUN: llc --mtriple=loongarch64  --relocation-model=pic < %s | FileCheck %s
+
+declare void @throw_exception()
+
+declare i32 @__gxx_personality_v0(...)
+
+declare ptr @__cxa_begin_catch(ptr)
+
+declare void @__cxa_end_catch()
+
+; CHECK-LABEL: test1:
+; CHECK: .cfi_startproc
+;; PersonalityEncoding = DW_EH_PE_indirect | DW_EH_PE_pcrel | DW_EH_PE_sdata4
+; CHECK-NEXT: .cfi_personality 155, DW.ref.__gxx_personality_v0
+;; LSDAEncoding = DW_EH_PE_pcrel | DW_EH_PE_sdata4
+; CHECK-NEXT: .cfi_lsda 27, .Lexception0
+
+define void @test1() personality ptr @__gxx_personality_v0 {
+entry:
+  invoke void @throw_exception() to label %try.cont unwind label %lpad
+
+lpad:
+  %0 = landingpad { ptr, i32 }
+          catch ptr null
+  %1 = extractvalue { ptr, i32 } %0, 0
+  %2 = tail call ptr @__cxa_begin_catch(ptr %1)
+  tail call void @__cxa_end_catch()
+  br label %try.cont
+
+try.cont:
+  ret void
+}
+
+; CHECK-LABEL: GCC_except_table0:
+; CHECK-NEXT: .Lexception0:
+; CHECK-NEXT: .byte 255 # @LPStart Encoding = omit
+;; TTypeEncoding = DW_EH_PE_indirect | DW_EH_PE_pcrel | DW_EH_PE_sdata4
+; CHECK-NEXT: .byte 155 # @TType Encoding = indirect pcrel sdata4
+; CHECK: .Lttbaseref0:
+;; CallSiteEncoding = dwarf::DW_EH_PE_uleb128
+; CHECK-NEXT: .byte 1                       # Call site Encoding = uleb128
+; CHECK-NEXT: .uleb128 .Lcst_end0-.Lcst_begin0
+; CHECK-NEXT: .Lcst_begin0:
+; CHECK-NEXT: .uleb128 .Ltmp0-.Lfunc_begin0   # >> Call Site 1 <<
+; CHECK-NEXT: .uleb128 .Ltmp1-.Ltmp0          #   Call between .Ltmp0 and .Ltmp1
+; CHECK-NEXT: .uleb128 .Ltmp2-.Lfunc_begin0   #     jumps to .Ltmp2
+; CHECK-NEXT: .byte 1                       #   On action: 1
+; CHECK-NEXT: .uleb128 .Ltmp1-.Lfunc_begin0   # >> Call Site 2 <<
+; CHECK-NEXT: .uleb128 .Lfunc_end0-.Ltmp1     #   Call between .Ltmp1 and .Lfunc_end0
+; CHECK-NEXT: .byte 0                       #     has no landing pad
+; CHECK-NEXT: .byte 0                       #   On action: cleanup