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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.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D131029
Files:
lldb/source/Plugins/UnwindAssembly/x86/x86AssemblyInspectionEngine.cpp
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;
}
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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