[Bug backtrace/29374] Internal-error when printing exception backtrace

["simark at simark dot ca" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=29374

Simon Marchi <simark at simark dot ca> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2022-07-24
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1
                 CC|                            |simark at simark dot ca

--- Comment #3 from Simon Marchi <simark at simark dot ca> ---
Thanks for the reproducer, I am able to reproduce.  And thanks for the
bisection.  The patch you found added some additional checks, and it looks like
it caught a pre-existing problem.

Here:

https://gitlab.com/gnutools/binutils-gdb/-/blob/6577f365ebdee7dda71cb996efa29d3714cbccd0/gdb/dwarf2/expr.c#L1027

We try to get the length of subobj_type, but it is a typedef whose actual size
hasn't been computed yet:

(top-gdb) p subobj_type.main_type.name
$1 = 0x6210001ef820 "Handler::key_type"
(top-gdb) p subobj_type.main_type.code
$2 = TYPE_CODE_TYPEDEF
(top-gdb) p subobj_type.length 
$3 = 0

If I add a check_typedef at the beginning of fetch_result, it looks like it
works:

>From 13d2d8b935f22ac2345c76a69ba009e583f9dc50 Mon Sep 17 00:00:00 2001
From: Simon Marchi <simon.marchi@polymtl.ca>
Date: Sat, 23 Jul 2022 21:41:55 -0400
Subject: [PATCH] patch

Change-Id: I182733ad08e34df40d8bcc47af72c482fabf4900
---
 gdb/dwarf2/expr.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/gdb/dwarf2/expr.c b/gdb/dwarf2/expr.c
index 592dbe19d562..d2b7a131de33 100644
--- a/gdb/dwarf2/expr.c
+++ b/gdb/dwarf2/expr.c
@@ -930,6 +930,11 @@ dwarf_expr_context::fetch_result (struct type *type,
struct type *subobj_type,
   if (subobj_type == nullptr)
     subobj_type = type;

+  /* Ensure that, if TYPE or SUBOBJ_TYPE are typedefs, their length is filled
+     in instead of being zero.  */
+  check_typedef (type);
+  check_typedef (subobj_type);
+
   if (this->m_pieces.size () > 0)
     {
       ULONGEST bit_size = 0;

base-commit: 4bce7cdaf481901edbc5ee47d953ea7e8efb56ca
-- 
2.37.1

$./gdb -nx --data-directory=data-directory -q -batch -ex "catch throw" -ex r
-ex bt a.out 
Catchpoint 1 (throw)

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Using host libthread_db library "/usr/lib/../lib/libthread_db.so.1".

Catchpoint 1 (exception thrown), 0x00007ffff7ca5e91 in __cxxabiv1::__cxa_throw
(obj=0x55555556af30, tinfo=0x555555557d20 <typeinfo for
std::runtime_error@GLIBCXX_3.4>, dest=0x7ffff7cbd370
<std::runtime_error::~runtime_error()>) at
/usr/src/debug/gcc/libstdc++-v3/libsupc++/eh_throw.cc:81
81      /usr/src/debug/gcc/libstdc++-v3/libsupc++/eh_throw.cc: No such file or
directory.
#0  0x00007ffff7ca5e91 in __cxxabiv1::__cxa_throw (obj=0x55555556af30,
tinfo=0x555555557d20 <typeinfo for std::runtime_error@GLIBCXX_3.4>,
dest=0x7ffff7cbd370 <std::runtime_error::~runtime_error()>) at
/usr/src/debug/gcc/libstdc++-v3/libsupc++/eh_throw.cc:81
#1  0x00005555555554a9 in Handler::find (this=this@entry=0x7fffffffdb20,
key=key@entry=@0x7fffffffdb1c: 0) at
/usr/include/c++/12.1.0/bits/new_allocator.h:90
#2  0x000055555555526e in Handler::operator() (key=@0x7fffffffdb1c: 0,
this=0x7fffffffdb20) at repro.cpp:14
#3  State::find (type=<optimized out>, this=0x7fffffffdb20) at repro.cpp:39
#4  main () at repro.cpp:49

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