Re: [PATCH] coredump: add core_pattern specifier for si_code

[Christian Brauner <brauner@kernel.org>]

On Tue, Mar 17, 2026 at 04:00:06PM +0100, Emanuele Rocca wrote:
> The specifiers supported by core_pattern include the option to indicate the
> signal number si_signo by using %s. Other than identifying which signal
> generated a core dump (eg: 11 for SIGSEGV), it is useful to know the reason why
> a certain signal was sent. The signal code si_code (eg: 2 for SEGV_ACCERR)
> provides this information.
> 
> Adding the signal code to core_pattern can benefit in particular sysadmins who
> pipe core dumps to user-space programs for later analysis. systemd-coredump(8)
> is a notable example of such programs.
> 
> Signed-off-by: Emanuele Rocca <emanuele.rocca@arm.com>
> ---
>  Documentation/admin-guide/sysctl/kernel.rst | 1 +
>  fs/coredump.c                               | 5 +++++
>  2 files changed, 6 insertions(+)
> 
> diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
> index 9aed74e65cf4..20177bd94514 100644
> --- a/Documentation/admin-guide/sysctl/kernel.rst
> +++ b/Documentation/admin-guide/sysctl/kernel.rst
> @@ -170,6 +170,7 @@ core_pattern
>  	%d		dump mode, matches ``PR_SET_DUMPABLE`` and
>  			``/proc/sys/fs/suid_dumpable``
>  	%s		signal number
> +	%n		signal code

Request %F which installs pidfd for the coredumping process into the
coredump helper then use the pidfd info ioctl in you binary with
PIDFD_INFO_EXIT | PIDFD_INFO_COREDUMP and you can retrieve the exit
status including the signal that was sent to the process.