[MC] Changes to help improve target specific symbol disassembly

Summary:
This commit slightly modifies the MCDisassembler, and llvm-objdump to
allow targets to also decode entire symbols.

WebAssembly uses the onSymbolStart hook it to decode preludes.
WebAssembly partially disassembles the symbol in its target specific
way; and then falls back to the normal flow of llvm-objdump.

AMDGPU needs it to decode kernel descriptors entirely, and move to the
next symbol.

This commit is to split the above task into 2.
- Changes to llvm-objdump and MC-layer without breaking WebAssembly code
  [ this commit ]
- AMDGPU's implementation of onSymbolStart that decodes kernel
  descriptors. [ https://reviews.llvm.org/D80713 ]

Reviewers: scott.linder, t-tye, sunfish, arsenm, jhenderson, MaskRay, aardappel

Reviewed By: scott.linder, jhenderson, aardappel

Subscribers: bcain, dschuff, wdng, tpr, sbc100, jgravelle-google, hiraditya, aheejin, MaskRay, rupprecht, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D80512

1 files changed, 8 insertions, 7 deletions

diff --git a/llvm/lib/Target/WebAssembly/Disassembler/WebAssemblyDisassembler.cpp b/llvm/lib/Target/WebAssembly/Disassembler/WebAssemblyDisassembler.cpp
index a8cb5d1..8f14de6 100644
--- a/llvm/lib/Target/WebAssembly/Disassembler/WebAssemblyDisassembler.cpp
+++ b/llvm/lib/Target/WebAssembly/Disassembler/WebAssemblyDisassembler.cpp
@@ -46,9 +46,10 @@ class WebAssemblyDisassembler final : public MCDisassembler {
   DecodeStatus getInstruction(MCInst &Instr, uint64_t &Size,
                               ArrayRef<uint8_t> Bytes, uint64_t Address,
                               raw_ostream &CStream) const override;
-  DecodeStatus onSymbolStart(StringRef Name, uint64_t &Size,
-                             ArrayRef<uint8_t> Bytes, uint64_t Address,
-                             raw_ostream &CStream) const override;
+  Optional<DecodeStatus> onSymbolStart(StringRef Name, uint64_t &Size,
+                                       ArrayRef<uint8_t> Bytes,
+                                       uint64_t Address,
+                                       raw_ostream &CStream) const override;
 
 public:
   WebAssemblyDisassembler(const MCSubtargetInfo &STI, MCContext &Ctx,
@@ -120,7 +121,7 @@ bool parseImmediate(MCInst &MI, uint64_t &Size, ArrayRef<uint8_t> Bytes) {
   return true;
 }
 
-MCDisassembler::DecodeStatus WebAssemblyDisassembler::onSymbolStart(
+Optional<MCDisassembler::DecodeStatus> WebAssemblyDisassembler::onSymbolStart(
     StringRef Name, uint64_t &Size, ArrayRef<uint8_t> Bytes, uint64_t Address,
     raw_ostream &CStream) const {
   Size = 0;
@@ -128,21 +129,21 @@ MCDisassembler::DecodeStatus WebAssemblyDisassembler::onSymbolStart(
     // Start of a code section: we're parsing only the function count.
     int64_t FunctionCount;
     if (!nextLEB(FunctionCount, Bytes, Size, false))
-      return MCDisassembler::Fail;
+      return None;
     outs() << "        # " << FunctionCount << " functions in section.";
   } else {
     // Parse the start of a single function.
     int64_t BodySize, LocalEntryCount;
     if (!nextLEB(BodySize, Bytes, Size, false) ||
         !nextLEB(LocalEntryCount, Bytes, Size, false))
-      return MCDisassembler::Fail;
+      return None;
     if (LocalEntryCount) {
       outs() << "        .local ";
       for (int64_t I = 0; I < LocalEntryCount; I++) {
         int64_t Count, Type;
         if (!nextLEB(Count, Bytes, Size, false) ||
             !nextLEB(Type, Bytes, Size, false))
-          return MCDisassembler::Fail;
+          return None;
         for (int64_t J = 0; J < Count; J++) {
           if (I || J)
             outs() << ", ";