Re: [PATCH] Fix crash in AIX when current working directory is NULL

[Keith Seitz <keiths@redhat.com>]

Hi,

On 6/22/26 2:11 AM, Aditya Vidyadhar Kamath wrote:
> From: Aditya Kamath <Aditya.Kamath1@ibm.com>
> 
> In AIX if we cannot read in the current directory we get,
> 

Thank you for the patch. I can confirm that this is independent of
architecture/OS. On x86_64 Fedora 43, we can also demonstrate the issue:

term1$ pwd
/home/keiths/tmp
term1$ mkdir gone && cd gone
term2$ rm -rf ~/tmp/gone
term1$ gdb -nx -q ~/tmp/simple
/home/keiths/gdb: ⚠️ warning: error finding working directory: No such 
file or directory
Reading symbols from /home/keiths/tmp/simple...
terminate called after throwing an instance of 'std::logic_error'
   what():  basic_string: construction from null is not valid

We've seen a number of similar issues throughout the years. Is it
possible to write a test for this?

> The reason for the same above is that in AIX, the variable current_directory in dwarf2/read.c
> can be NULL if getcwd () fails during GDB initialisation. When this happens the dwarf2_per_bfd
> construction initialisation list captured_cwd to NULL resulting in this segmentation fault shown above.

I apologize for being pedantic, but this is more accurately described as 
a (abort due to a) std::logic_error.

> There are two reasons this happened:
> 1: The current working directory got deleted in another terminal.
> 2: Insufficient permission to read the current directory or its parent/predicissor directory.

Typo "predicissor". Did you mean "predecessor?"

> 
> This patch is a fix to the same.
> 
> Afer this fix we get GDB loaded correctly.

Typo "After"

> gdb ~/gdb_tests/simple_test
> gdb: warning: error finding working directory: A parameter must be a directory.
> GNU gdb (GDB) 18.0.50.20260619-git
> Copyright (C) 2026 Free Software Foundation, Inc.
> License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
> This is free software: you are free to change and redistribute it.
> There is NO WARRANTY, to the extent permitted by law.
> Type "show copying" and "show warranty" for details.
> This GDB was configured as "powerpc64-ibm-aix7.2.0.0".
> Type "show configuration" for configuration details.
> For bug reporting instructions, please see:
> <https://www.gnu.org/software/gdb/bugs/>.
> 
> +------------------------------------------------------------------------------+
> | Find the GDB manual online at:                                               |
> | http://www.gnu.org/software/gdb/documentation/.                              |
> | For help, type "help".                                                       |
> | Type "apropos word" to search for commands related to "word".                |
> +------------------------------------------------------------------------------+
> 
> Reading symbols from //gdb_tests/simple_test...
> (gdb) q
> ---
>   gdb/dwarf2/read.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
> index 84b1480dbcb..7962acc784d 100644
> --- a/gdb/dwarf2/read.c
> +++ b/gdb/dwarf2/read.c
> @@ -859,7 +859,7 @@ dwarf2_per_bfd::dwarf2_per_bfd (bfd *obfd, const dwarf2_debug_sections *names,
>   				bool can_copy_)
>     : obfd (obfd),
>       can_copy (can_copy_),
> -    captured_cwd (current_directory),
> +    captured_cwd (current_directory == NULL ? "" : current_directory),

Please use "nullptr" instead.

>       captured_debug_dir (debug_file_directory)
>   {
>     if (names == NULL)

While this fix does catch this one specific place, I wonder if this bug
lurks elsewhere. For example, in main.c, when getcwd() is called and
returns NULL, gdb warns the user and leaves current_directory as NULL.

Changing that so that current_directory isn't NULL also fixes this
problem and could prevent(?) other similar problems. Of course, that
kind of change could introduce some sort of API semantic inconsistencies
with current_directory which likely would require more (invasive)
changes.

In any case, I am just asking. Your patch is simple and minimally
invasive. Nonetheless, if it is possible, I would really like a
test for this.

Keith