[Lldb-commits] [PATCH] D131029: [NFC] Remove no-op code, duplicated, with multiple confusing comments, from x86AssemblyInspectionEngine::jmp_to_reg_p

Jason Molenda via Phabricator via lldb-commits lldb-commits at lists.llvm.org
Tue Aug 2 16:16:53 PDT 2022

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Thanks to @fixathon for catching this code I added in https://reviews.llvm.org/D62764.  This method clears the lower 3 bits of the second byte of an instruction, then compares it to a few values including 0x20 (fine) and 0x24, twice, with comments that seem to contradict the behavior.  Of course, having masked off the low 3 bits, these duplicated entries are never matched.

  rG LLVM Github Monorepo



Index: lldb/source/Plugins/UnwindAssembly/x86/x86AssemblyInspectionEngine.cpp
--- lldb/source/Plugins/UnwindAssembly/x86/x86AssemblyInspectionEngine.cpp
+++ lldb/source/Plugins/UnwindAssembly/x86/x86AssemblyInspectionEngine.cpp
@@ -682,10 +682,6 @@
   // The second byte is a ModR/M /4 byte, strip off the registers
   uint8_t second_byte_sans_reg = *(m_cur_insn + 1) & ~7;
-  // Don't handle 0x24 disp32, because the target address is
-  // knowable statically - pc_rel_branch_or_jump_p() will
-  // return the target address.
   // [reg]
   if (second_byte_sans_reg == 0x20)
     return true;
@@ -702,17 +698,6 @@
   if (second_byte_sans_reg == 0xe0)
     return true;
-  // disp32
-  // jumps to an address stored in memory, the value can't be cached
-  // in an unwind plan.
-  if (second_byte_sans_reg == 0x24)
-    return true;
-  // use SIB byte
-  // ff 24 fe  jmpq   *(%rsi,%rdi,8)
-  if (second_byte_sans_reg == 0x24)
-    return true;
   return false;

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