Erroneous Dissassembly obtained when breakpoint is inserted

[llvmbot]

Bugzilla Link	23613
Resolution	FIXED
Resolved on	May 22, 2015 03:49
Version	unspecified
OS	Linux
Attachments	C++ source file
Reporter	LLVM Bugzilla Contributor
CC	@labath

Extended Description

When a breakpoint is inserted at an instruction, the subsequent instructions are erroneously decoded by LLDB. Possible reason could be that while decoding instructions (when a breakpoint is also inserted), LLDB should substitute the complete original instruction before decoding. Instead the dissassembly is decoded correctly till the breakpoint instruction but since the breakpoint instruction is basically modifying 1 byte of an already existing instruction, LLDB interprets the rest of the bytes as new instructions.

Disassembly by GDB

0x0000000000400922 <+0>: push %rbp
0x0000000000400923 <+1>: mov %rsp,%rbp
0x0000000000400926 <+4>: sub $0x30,%rsp
0x000000000040092a <+8>: mov %rdi,-0x18(%rbp)
0x000000000040092e <+12>: mov %esi,-0x1c(%rbp)
0x0000000000400931 <+15>: mov %edx,-0x20(%rbp)
0x0000000000400934 <+18>: mov %ecx,-0x24(%rbp)
=> 0x0000000000400937 <+21>: mov -0x1c(%rbp),%eax
0x000000000040093a <+24>: cmp -0x20(%rbp),%eax
0x000000000040093d <+27>: jle 0x40094b <binary_search(int*, int, int, int)+41>
0x000000000040093f <+29>: movl $0xffffffff,-0x8(%rbp)
0x0000000000400946 <+36>: jmpq 0x4009d9 <binary_search(int*, int, int, int)+183>

Corresponding Disassembly by LLDB

0x400922 <+0>:  pushq  %rbp
0x400923 <+1>:  movq   %rsp, %rbp
0x400926 <+4>:  subq   $0x30, %rsp
0x40092a <+8>:  movq   %rdi, -0x18(%rbp)
0x40092e <+12>: movl   %esi, -0x1c(%rbp)
0x400931 <+15>: movl   %edx, -0x20(%rbp)
0x400934 <+18>: movl   %ecx, -0x24(%rbp)

-> 0x400937 <+21>: int3
0x400938 <+22>: inb $0x3b, %al
0x40093b <+25>: loopne 0x4009bc ; <+154> at test.cpp:34
0x40093e <+28>: orb $-0x39, %al
0x400940 <+30>: clc

As it can be seen in the disassembly by LLDB, after breakpoint at <+21> the instructions are not correctly decoded.

Steps to reproduce

1. Compile attached source with g++ (with -g option)
2. Start debugging with LLDB
3. Insert breakpoint at binary_search (b binary_search)
4. Execute command "disassemble"

[labath]

This bug should be fixed in the SVN. If it still persists with the latest version of lldb, please reopen.

[llvmbot]

Is the fix also available in the git repository ? when merged into the git repository please inform me , I will check again.

[labath]

The git repository is automatically synced with SVN. Are you saying this still happens with the latest git?

[llvmbot]

Ok, I checked with the updated LLDB, this issue is fixed. I wasn't aware of the frequency of the synchronization between GIT and SVN.