[binutils-gdb] gdb: initialize ctf_context::builder in create_partial_symtab

[binutils-gdb] gdb: initialize ctf_context::builder in create_partial_symtab

[Simon Marchi]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=59f837cb11e3b96c581fe23b79f6995b7c8177ee

commit 59f837cb11e3b96c581fe23b79f6995b7c8177ee
Author: Simon Marchi <simon.marchi@polymtl.ca>
Date:   Thu Mar 31 14:20:02 2022 -0400

    gdb: initialize ctf_context::builder in create_partial_symtab
    
    I built a random project with -gctf, in order to test the CTF support in
    GDB.  With my ASan/UBSan/etc-enabled build of GDB, I get:
    
        $ ./gdb --data-directory=data-directory /tmp/babeltrace-ctf/src/lib/.libs/libbabeltrace2.so.0.0.0
        ...
        Reading symbols from /tmp/babeltrace-ctf/src/lib/.libs/libbabeltrace2.so.0.0.0...
        /home/simark/src/binutils-gdb/gdb/ctfread.c:1545:31: runtime error: member call on misaligned address 0xbebebebebebebebe for type 'struct buildsym_compunit', which requires 8 byte alignment
        0xbebebebebebebebe: note: pointer points here
    
    The 0xbebebebebebebebe value is a sign that the ctf_context::builder
    field is uninitialized.  The problem probably goes under the radar if
    the field happens to be zero-initialized, because ctf_start_archive
    contains this code:
    
      if (ccx->builder == nullptr)
        {
          ccx->builder = new buildsym_compunit (of,
                          of->original_name, nullptr, language_c, 0);
    
    If the field was zero-initialized (by chance), this will create a new
    buildsym_compunit.  But if the field was purposely filled with random
    bytes by one of the sanitizers, we won't create a buildsym_compunit here
    and we'll continue with ccx->builder equal to 0xbebebebebebebebe.
    
    Fix this the easy way by initializing ccx->builder where the other
    ctf_context fields are initialized (yeah, this code could be made nicer
    C++, but I am going for the obvious fix here).
    
    With this patch, this passes cleanly on my system:
    
      $ make check TESTS="gdb.ctf/*.exp" RUNTESTFLAGS="CC_FOR_TARGET=/opt/gcc/git/bin/gcc"
      # of expected passes            40
    
    ... where /opt/gcc/git/bin/gcc is a gcc with CTF support, given my
    system gcc does not have it.
    
    Change-Id: Idea1b0cf3e3708b72ecb16b1b60222439160f9b9

Diff:
---
 gdb/ctfread.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/gdb/ctfread.c b/gdb/ctfread.c
index 585c664cce2..8da38cc70af 100644
--- a/gdb/ctfread.c
+++ b/gdb/ctfread.c
@@ -1449,6 +1449,7 @@ create_partial_symtab (const char *name,
   pst->context.of = objfile;
   pst->context.partial_symtabs = partial_symtabs;
   pst->context.pst = pst;
+  pst->context.builder = nullptr;
 
   return pst;
 }