Re: [PATCH v2 2/5] Don't return stale data from fbsd_pid_to_exec_file for kernel processes.

[Simon Marchi <simark@simark.ca>]

On 2018-01-03 08:49 PM, John Baldwin wrote:
> For processes without an associated executable (such as kernel processes),
> the kern.proc.pathname.<pid> system control node returns a length of zero
> without modifying the user's buffer.  Detect this case and return NULL
> rather than the previous contents of the static buffer 'buf'.
> 
> gdb/ChangeLog:
> 
> 	* fbsd-nat.c (fbsd_pid_to_exec_file) [KERN_PROC_PATHNAME]: Return
> 	NULL for an empty pathname.
> ---
>  gdb/ChangeLog  | 5 +++++
>  gdb/fbsd-nat.c | 2 +-
>  2 files changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/gdb/ChangeLog b/gdb/ChangeLog
> index 29cfbb287b..804dd4f402 100644
> --- a/gdb/ChangeLog
> +++ b/gdb/ChangeLog
> @@ -1,3 +1,8 @@
> +2018-01-03  John Baldwin  <jhb@FreeBSD.org>
> +
> +	* fbsd-nat.c (fbsd_pid_to_exec_file) [KERN_PROC_PATHNAME]: Return
> +	NULL for an empty pathname.
> +
>  2018-01-03  John Baldwin  <jhb@FreeBSD.org>
>  
>  	* fbsd-tdep.c (KVE_STRUCTSIZE, KVE_START, KVE_END, KVE_OFFSET)
> diff --git a/gdb/fbsd-nat.c b/gdb/fbsd-nat.c
> index ec4eed9abe..7b1d1bf148 100644
> --- a/gdb/fbsd-nat.c
> +++ b/gdb/fbsd-nat.c
> @@ -63,7 +63,7 @@ fbsd_pid_to_exec_file (struct target_ops *self, int pid)
>    mib[3] = pid;
>    buflen = sizeof buf;
>    if (sysctl (mib, 4, buf, &buflen, NULL, 0) == 0)
> -    return buf;
> +    return buflen == 0 ? NULL : buf;
>  #endif
>  
>    xsnprintf (name, PATH_MAX, "/proc/%d/exe", pid);
> 

LGTM, but maybe add a comment saying in what situation the sysctl can
return a buflen of 0.

Does the alternative method that reads from /proc/<pid>/exe work in that
case too?

Simon