Re: [PATCH] Linux/ptrace: don't convert ptids when asking inf-ptrace layer to resume LWP

[Mark Kettenis <mark dot kettenis at xs4all dot nl>]

> From: Pedro Alves <palves@redhat.com>
> Date: Tue, 3 Mar 2015 13:33:44 +0000
> 
> Tested on x86-64 Fedora 20, -m32.
> 
> gdb/ChangeLog:
> 2015-03-03  Pedro Alves  <palves@redhat.com>
> 
> 	* i386-linux-nat.c (i386_linux_resume): Get the ptrace PID out of
> 	the lwp field of ptid.  Pass the full ptid to get_thread_regcache.
> 	* inf-ptrace.c (get_ptrace_pid): New function.
> 	(inf_ptrace_resume): Use it.
> 	* linux-nat.c (linux_resume_one_lwp): Pass the LWP's ptid ummodified
> 	to the lower layer.
> ---
>  gdb/ChangeLog        |  9 +++++++++
>  gdb/i386-linux-nat.c |  5 ++---
>  gdb/inf-ptrace.c     | 25 ++++++++++++++++++++++---
>  gdb/linux-nat.c      |  6 +-----
>  4 files changed, 34 insertions(+), 11 deletions(-)

I have some fear this is going to break non-Linux targets.

> --- a/gdb/inf-ptrace.c
> +++ b/gdb/inf-ptrace.c
> @@ -289,6 +289,22 @@ inf_ptrace_stop (struct target_ops *self, ptid_t ptid)
>    kill (-inferior_process_group (), SIGINT);
>  }
>  
> +/* Return which PID to pass to ptrace in order to observe/control the
> +   tracee identified by PTID.  */
> +
> +static pid_t
> +get_ptrace_pid (ptid_t ptid)
> +{
> +  pid_t pid;
> +
> +  /* If we have an LWPID to work with, use it.  Otherwise, we're
> +     dealing with a non-threaded program/target.  */
> +  pid = ptid_get_lwp (ptid);
> +  if (pid == 0)
> +    pid = ptid_get_pid (ptid);
> +  return pid;
> +}
> +
>  /* Resume execution of thread PTID, or all threads if PTID is -1.  If
>     STEP is nonzero, single-step it.  If SIGNAL is nonzero, give it
>     that signal.  */
> @@ -297,13 +313,16 @@ static void
>  inf_ptrace_resume (struct target_ops *ops,
>  		   ptid_t ptid, int step, enum gdb_signal signal)
>  {
> -  pid_t pid = ptid_get_pid (ptid);
> +  pid_t pid;
> +
>    int request;

Please don't introduce a blank line here.

> -  if (pid == -1)
> +  if (ptid_equal (minus_one_ptid, ptid))
>      /* Resume all threads.  Traditionally ptrace() only supports
>         single-threaded processes, so simply resume the inferior.  */
> -    pid = ptid_get_pid (inferior_ptid);
> +    pid = get_ptrace_pid (inferior_ptid);

This defenitely should remain ptid_get_pid(); you want to resume the
entire process and not an individual thread.

> +  else
> +    pid = get_ptrace_pid (ptid);

This should work for OpenBSD, and probably works for FreeBSD.  It
won't work for NetBSD, but they will probably need their own
implementation of this function, so it's probably fine.