[JITLink][RISCV] Implement eh_frame handling

[Hahnfeld]

Summary

This requires adding Delta{32,64} and NegDelta32 edge kinds that cannot be mapped to existing relocations.

[Hahnfeld]

FWIW I thought we could reuse the ADD* relocations here, but it turns out the documentation had a sign error in the fixup expressions; I corrected that in rGf9d55410e242761d6d8697def28a86342560a60c.

[jobnoorman]

It seems I created a PR implementing essentially the same thing :) Since both patches are equivalent, I don't mind which one gets merged.

My PR has one extra test case that checks if the values for CIE_pointer, address_range, and DW_CFA_advance_loc are patched correctly. It might be worth adding that test case to this patch.

llvm/lib/ExecutionEngine/JITLink/ELF_riscv.cpp

462

This is the same as R_RISCV_32_PCREL so maybe just reuse that one? At some point, R_RISCV_32_PCREL should be renamed to Delta32 though.

473

Add range check?

[Hahnfeld]

llvm/lib/ExecutionEngine/JITLink/ELF_riscv.cpp

462

Actually the (positive) Delta edges are not needed at all; the hypothetical AddFDEToCIEEdges discussed in https://reviews.llvm.org/D157802 only needs NegDelta32. That's another reason why I think it's the way to go.

[jobnoorman]

llvm/lib/ExecutionEngine/JITLink/ELF_riscv.cpp

462

Ah yes, you're right. I see the point about AddFDEToCIEEdges but I worry a bit about the (non-trivial) code duplication it would introduce. The documentation of EHFrameEdgeFixer mentions that it should be fine to provide Edge::Invalid for unsupported edge kinds but the implementation doesn't seem to check for that. Maybe this could be a way to configure it to not do more than necessary on RISC-V?

[Hahnfeld]

Superseded by https://github.com/llvm/llvm-project/pull/68253 which implements only one newly needed edge kind.

llvm/include/llvm/ExecutionEngine/JITLink/riscv.h

enum EdgeKind_riscv : Edge::Kind {
   /// if it succeeds, or with R_RISCV_CALL_PLT if it fails.
   CallRelaxable,
 
   /// Alignment requirement used by linker relaxation.
   ///
   /// Linker relaxation will use this to ensure all code sequences are properly
   /// aligned and then remove these edges from the graph.
   AlignRelaxable,
+
+  /// 32-bit delta.
+  ///
+  /// Fixup expression:
+  ///   Fixup <- Target - Fixup + Addend
+  Delta32,
+
+  /// 64-bit delta.
+  ///
+  /// Fixup expression:
+  ///   Fixup <- Target - Fixup + Addend
+  Delta64,
+
+  /// 32-bit negative delta.
+  ///
+  /// Fixup expression:
+  ///   Fixup <- Fixup - Target + Addend
+  NegDelta32,
 };
 
 /// Returns a string name for the given riscv edge. For debugging purposes
 /// only
 const char *getEdgeKindName(Edge::Kind K);
 } // namespace riscv
 } // namespace jitlink
 } // namespace llvm
 
 #endif

llvm/lib/ExecutionEngine/JITLink/ELF_riscv.cpp

 //===------- ELF_riscv.cpp -JIT linker implementation for ELF/riscv -------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
 // ELF/riscv jit-link implementation.
 //
 //===----------------------------------------------------------------------===//
 
 #include "llvm/ExecutionEngine/JITLink/ELF_riscv.h"
+#include "EHFrameSupportImpl.h"
 #include "ELFLinkGraphBuilder.h"
 #include "JITLinkGeneric.h"
 #include "PerGraphGOTAndPLTStubsBuilder.h"
 #include "llvm/BinaryFormat/ELF.h"
+#include "llvm/ExecutionEngine/JITLink/DWARFRecordSectionSplitter.h"
 #include "llvm/ExecutionEngine/JITLink/JITLink.h"
 #include "llvm/ExecutionEngine/JITLink/riscv.h"
 #include "llvm/Object/ELF.h"
 #include "llvm/Object/ELFObjectFile.h"
 #include "llvm/Support/Endian.h"
 
 #define DEBUG_TYPE "jitlink"
+
 using namespace llvm;
 using namespace llvm::jitlink;
 using namespace llvm::jitlink::riscv;
 
 namespace {
 
 class PerGraphGOTAndPLTStubsBuilder_ELF_riscv
     : public PerGraphGOTAndPLTStubsBuilder<
case R_RISCV_32_PCREL: {
       int64_t Value = E.getTarget().getAddress() + E.getAddend() - FixupAddress;
       int64_t Word32 = Value & 0xffffffff;
       *(little32_t *)FixupPtr = Word32;
       break;
     }
     case AlignRelaxable:
       // Ignore when the relaxation pass did not run
       break;
+    case Delta32: {
+      int64_t Value = E.getTarget().getAddress() - FixupAddress + E.getAddend();
+      *(little32_t *)FixupPtr = static_cast<uint32_t>(Value);
+      break;
+    }
+    case Delta64: {
+      int64_t Value = E.getTarget().getAddress() - FixupAddress + E.getAddend();
+      *(little64_t *)FixupPtr = static_cast<uint64_t>(Value);
+      break;
+    }
+    case NegDelta32: {
+      int64_t Value = FixupAddress - E.getTarget().getAddress() + E.getAddend();
+      *(little32_t *)FixupPtr = static_cast<uint32_t>(Value);
+      break;
+    }
     }
     return Error::success();
   }
 };
 
 namespace {
 
 struct SymbolAnchor {
createLinkGraphFromELFObject_riscv(MemoryBufferRef ObjectBuffer) {
   }
 }
 
 void link_ELF_riscv(std::unique_ptr<LinkGraph> G,
                     std::unique_ptr<JITLinkContext> Ctx) {
   PassConfiguration Config;
   const Triple &TT = G->getTargetTriple();
   if (Ctx->shouldAddDefaultTargetPasses(TT)) {
+
+    Config.PrePrunePasses.push_back(DWARFRecordSectionSplitter(".eh_frame"));
+    Config.PrePrunePasses.push_back(EHFrameEdgeFixer(
+        ".eh_frame", G->getPointerSize(), R_RISCV_32, R_RISCV_64,
+        Delta32, Delta64, NegDelta32));
+    Config.PrePrunePasses.push_back(EHFrameNullTerminator(".eh_frame"));
+
     if (auto MarkLive = Ctx->getMarkLivePass(TT))
       Config.PrePrunePasses.push_back(std::move(MarkLive));
     else
       Config.PrePrunePasses.push_back(markAllSymbolsLive);
     Config.PostPrunePasses.push_back(
         PerGraphGOTAndPLTStubsBuilder_ELF_riscv::asPass);
     Config.PostAllocationPasses.push_back(relax);
   }

llvm/lib/ExecutionEngine/JITLink/riscv.cpp

const char *getEdgeKindName(Edge::Kind K) {
   case R_RISCV_SET32:
     return "R_RISCV_SET32";
   case R_RISCV_32_PCREL:
     return "R_RISCV_32_PCREL";
   case CallRelaxable:
     return "CallRelaxable";
   case AlignRelaxable:
     return "AlignRelaxable";
+  case Delta32:
+    return "Delta32";
+  case Delta64:
+    return "Delta64";
+  case NegDelta32:
+    return "NegDelta32";
   }
   return getGenericEdgeKindName(K);
 }
 } // namespace riscv
 } // namespace jitlink
 } // namespace llvm

llvm/test/ExecutionEngine/JITLink/RISCV/ELF_ehframe.s

+# REQUIRES: asserts
+# RUN: llvm-mc -triple=riscv64-linux-gnu -filetype=obj -o %t %s
+# RUN: llvm-jitlink -noexec -phony-externals -debug-only=jitlink %t 2>&1 | \
+# RUN:   FileCheck %s
+
+# Check that splitting of eh-frame sections works.
+#
+# CHECK: DWARFRecordSectionSplitter: Processing .eh_frame...
+# CHECK:  Processing block at
+# CHECK:    Processing CFI record at
+# CHECK:      Extracted {{.*}} section = .eh_frame
+# CHECK:    Processing CFI record at
+# CHECK:      Extracted {{.*}} section = .eh_frame
+# CHECK: EHFrameEdgeFixer: Processing .eh_frame in "{{.*}}"...
+# CHECK:   Processing block at
+# CHECK:     Processing CFI record at
+# CHECK:       Record is CIE
+# CHECK:   Processing block at
+# CHECK:     Processing CFI record at
+# CHECK:       Record is FDE
+# CHECK:         Adding edge at {{.*}} to CIE at: {{.*}}
+# CHECK:         Existing edge at {{.*}} to PC begin at {{.*}}
+# CHECK:         Adding keep-alive edge from target at {{.*}} to FDE at {{.*}}
+
+  .text
+  .attribute  4, 16
+  .attribute  5, "rv64i2p1_m2p0_a2p1_f2p2_d2p2_c2p0_zicsr2p0"
+  .file "catch.cpp"
+  .globl  main                            # -- Begin function main
+  .p2align  1
+  .type main,@function
+main:                                   # @main
+.Lfunc_begin0:
+  .cfi_startproc
+  .cfi_personality 155, DW.ref.__gxx_personality_v0
+  .cfi_lsda 27, .Lexception0
+# %bb.0:
+  addi  sp, sp, -16
+  .cfi_def_cfa_offset 16
+  sd  ra, 8(sp)                       # 8-byte Folded Spill
+  .cfi_offset ra, -8
+  li  a0, 4
+  call  __cxa_allocate_exception@plt
+  li  a1, 1
+  sw  a1, 0(a0)
+.Ltmp0:
+.Lpcrel_hi0:
+  auipc a1, %got_pcrel_hi(_ZTIi)
+  ld  a1, %pcrel_lo(.Lpcrel_hi0)(a1)
+  li  a2, 0
+  call  __cxa_throw@plt
+.Ltmp1:
+# %bb.1:
+.LBB0_2:
+.Ltmp2:
+  call  __cxa_begin_catch@plt
+.Lpcrel_hi1:
+  auipc a0, %pcrel_hi(.Lstr)
+  addi  a0, a0, %pcrel_lo(.Lpcrel_hi1)
+  call  puts@plt
+  call  __cxa_end_catch@plt
+  li  a0, 0
+  ld  ra, 8(sp)                       # 8-byte Folded Reload
+  addi  sp, sp, 16
+  ret
+.Lfunc_end0:
+  .size main, .Lfunc_end0-main
+  .cfi_endproc
+  .section  .gcc_except_table,"a",@progbits
+  .p2align  2, 0x0
+GCC_except_table0:
+.Lexception0:
+  .byte 255                             # @LPStart Encoding = omit
+  .byte 155                             # @TType Encoding = indirect pcrel sdata4
+  .uleb128 .Lttbase0-.Lttbaseref0
+.Lttbaseref0:
+  .byte 3                               # Call site Encoding = udata4
+  .uleb128 .Lcst_end0-.Lcst_begin0
+.Lcst_begin0:
+  .word .Lfunc_begin0-.Lfunc_begin0     # >> Call Site 1 <<
+  .word .Ltmp0-.Lfunc_begin0            #   Call between .Lfunc_begin0 and .Ltmp0
+  .word 0                               #     has no landing pad
+  .byte 0                               #   On action: cleanup
+  .word .Ltmp0-.Lfunc_begin0            # >> Call Site 2 <<
+  .word .Ltmp1-.Ltmp0                   #   Call between .Ltmp0 and .Ltmp1
+  .word .Ltmp2-.Lfunc_begin0            #     jumps to .Ltmp2
+  .byte 1                               #   On action: 1
+  .word .Ltmp1-.Lfunc_begin0            # >> Call Site 3 <<
+  .word .Lfunc_end0-.Ltmp1              #   Call between .Ltmp1 and .Lfunc_end0
+  .word 0                               #     has no landing pad
+  .byte 0                               #   On action: cleanup
+.Lcst_end0:
+  .byte 1                               # >> Action Record 1 <<
+                                        #   Catch TypeInfo 1
+  .byte 0                               #   No further actions
+  .p2align  2, 0x0
+                                        # >> Catch TypeInfos <<
+  .word 0                               # TypeInfo 1
+.Lttbase0:
+  .p2align  2, 0x0
+                                        # -- End function
+  .type .Lstr,@object                   # @str
+  .section  .rodata.str1.1,"aMS",@progbits,1
+.Lstr:
+  .asciz  "Caught!"
+  .size .Lstr, 8
+
+  .hidden DW.ref.__gxx_personality_v0
+  .weak DW.ref.__gxx_personality_v0
+  .section  .data.DW.ref.__gxx_personality_v0,"aGw",@progbits,DW.ref.__gxx_personality_v0,comdat
+  .p2align  3, 0x0
+  .type DW.ref.__gxx_personality_v0,@object
+  .size DW.ref.__gxx_personality_v0, 8
+DW.ref.__gxx_personality_v0:
+  .quad __gxx_personality_v0
+  .ident  "clang version 18.0.0"
+  .section  ".note.GNU-stack","",@progbits
+  .addrsig
+  .addrsig_sym __gxx_personality_v0
+  .addrsig_sym _ZTIi