[DTrace-devel] [PATCH v2] dtprobed: use /proc/$pid/map_files, not the filename of the mapping

[Eugene Loh]

Reviewed-by: Eugene Loh <eugene.loh at oracle.com>

On 1/20/26 11:20, Nick Alcock via DTrace-devel wrote:
> Instead of using prf->prf_mapname (which resolves to the mapped file's
> target), use Pmap_mapfile_name() to get the actual
> /proc/$pid/map_files/* path.  These magic symlinks can be opened even
> when their corresponding files are deleted or in an inaccessible
> filesystem namespace, ensuring we can read the mapping contents
> reliably.  DTrace already does this to read mappings during USDT probe
> lookup.
>
> Fixes issues with probes in paths like /home when dtprobed
> is sandboxed by systemd.
>
> Tested on both systemd and non-systemd (non-jailed) systems, with USDT
> programs running out of /tmp, /usr/local and /home.
>
> Signed-off-by: Nick Alcock <nick.alcock at oracle.com>
> ---
>   dtprobed/dtprobed.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/dtprobed/dtprobed.c b/dtprobed/dtprobed.c
> index a808586559d96..9a6928055cd13 100644
> --- a/dtprobed/dtprobed.c
> +++ b/dtprobed/dtprobed.c
> @@ -487,7 +487,7 @@ handle_usdt_notes(pid_t pid, uintptr_t addr)
>   		fuse_log(FUSE_LOG_ERR, "%i: dtprobed: cannot look up mapping (process dead?)\n",
>   			 pid);
>   		goto out;
> -	} else if ((fn = prf->prf_mapname) == NULL) {
> +	} else if ((fn = Pmap_mapfile_name(P, mapp)) == NULL) {
>   		fuse_log(FUSE_LOG_ERR, "%i: dtprobed: cannot look up mapname (process dead?)\n",
>   			 pid);
>   		goto out;
>
> base-commit: 6e94c7d0a253806f85c39ff5f4e32a800d4cb6b6