[binutils-gdb] gdb: fix use of uninitialised gdb_printing_disassembler::m_in_comment

[binutils-gdb] gdb: fix use of uninitialised gdb_printing_disassembler::m_in_comment

[Andrew Burgess]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=554128418b4f1328bb956d5926f24bfd56fd45ea

commit 554128418b4f1328bb956d5926f24bfd56fd45ea
Author: Andrew Burgess <aburgess@redhat.com>
Date:   Wed Jul 20 13:00:40 2022 +0100

    gdb: fix use of uninitialised gdb_printing_disassembler::m_in_comment
    
    Simon pointed out that gdb_printing_disassembler::m_in_comment can be
    used uninitialised by the Python disassembler API code.  This issue
    was spotted when GDB was built with the undefined behaviour sanitizer,
    and causes the gdb.python/py-disasm.exp test to fail like this:
    
      (gdb) PASS: gdb.python/py-disasm.exp: global_disassembler=GlobalPreInfoDisassembler: python add_global_disassembler(GlobalPreInfoDisassembler)
      disassemble main
      Dump of assembler code for function main:
         0x0000555555555119 <+0>:     push   %rbp
         0x000055555555511a <+1>:     mov    %rsp,%rbp
         0x000055555555511d <+4>:     nop
      /home/user/src/binutils-gdb/gdb/disasm.h:144:12: runtime error: load of value 118, which is not a valid value for type 'bool'
    
    The problem is that in disasmpy_builtin_disassemble we create a new
    instance of gdbpy_disassembler, which is a sub-class of
    gdb_printing_disassembler, however, the m_in_comment field is never
    initialised.
    
    This commit fixes the issue by providing a default initialisation
    value for m_in_comment in disasm.h.  As we only ever disassemble a
    single instruction in disasmpy_builtin_disassemble then we don't need
    to worry about reseting m_in_comment back to false after the single
    instruction has been disassembled.
    
    With this commit the above issue is resolved and
    gdb.python/py-disasm.exp now passes.

Diff:
---
 gdb/disasm.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/gdb/disasm.h b/gdb/disasm.h
index 2921d537e0a..09cb3921767 100644
--- a/gdb/disasm.h
+++ b/gdb/disasm.h
@@ -166,7 +166,7 @@ private:
      uses styled output and emits a start of comment character.  It is up
      to the code that uses this disassembler class to reset this flag back
      to false at a suitable time (e.g. at the end of every line).  */
-  bool m_in_comment;
+  bool m_in_comment = false;
 };
 
 /* A basic disassembler that doesn't actually print anything.  */