Re: [PATCH 2/2] gdb: use current executable for 'remote exec-file' in some cases

[Eli Zaretskii <eliz@gnu.org>]

> From: Andrew Burgess <aburgess@redhat.com>
> Cc: Andrew Burgess <aburgess@redhat.com>,
> 	Eli Zaretskii <eliz@gnu.org>
> Date: Sat, 11 Oct 2025 14:34:04 +0100
> 
> This commit allows GDB to make use of the file set with the 'file'
> command when starting a new inferior on an extended-remote target.
> There are however some restrictions.
> 
> If the user has used 'set remote exec-file', then this setting is
> always used in preference to the file set with the 'file' command.
> 
> Similarly, if the qExecAndArgs packet has succeeded, and GDB knows
> that the remote target has an executable set, then this will be used
> in preference to the file set with the 'file' command; this preserves
> GDB's existing behaviour.  In effect, when GDB connects to the remote
> target, the remote sets the 'remote exec-file' and this prevents GDB
> from using the 'file' filename.
> 
> And, GDB can only use the file set with the 'file' command if it
> believes that both GDB and the remote target will both be able to
> access this file.  This means that one of these is true:
> 
>   + the the remote_target::filesystem_is_local function returns
>     true (see the implementation of that function for details of when
>     this can happen).  This means GDB and the remote target can see
>     the same file system, GDB can just use the current executable's
>     filename as is, or
> 
>   + the user has set the 'file' to something with a 'target:' prefix,
>     e.g. 'file target:/path/to/exec'.  In this last case, GDB will use
>     the exec filename without the 'target:' prefix, this filename is,
>     by definition, something the remote target can see, or
> 
>   + the sysroot has been updated by the user and no longer contains a
>     'target:' prefix.  In this case, if the 'file' filename is within
>     the sysroot, then it is assumed the remote will also be able to
>     see a file with the same filename.  For example, if the sysroot is
>     '/aa/', and the current executable is '/aa/bb/cc', then GDB will
>     tell the remote to run '/bb/cc'.  One common case here is when the
>     sysroot is set to the empty string, which is usually done when GDB
>     and the remote target can see the same filesystem, in this case
>     GDB will use the current executable's filename unmodified.
> 
> If one of these conditions is met, then GDB will use the current
> executable's filename (with possible modifications as mentioned
> above), when starting a new extended-remote inferior, in all other
> cases, GDB will use the file name  set with 'set remote exec-file'.
> 
> This change could be useful any time a user is running a remote target
> on the same machine as GDB, but I am specifically thinking of the case
> where GDB is using a tool other than gdbserver, e.g. valgrind, as this
> saves one additional step that a user must remember.  The current
> steps to start valgrind with GDB, as given on the valgrind
> website (https://valgrind.org/docs/manual/manual-core-adv.html) are:
> 
>   $ gdb prog
>   (gdb) set remote exec-file prog
>   (gdb) set sysroot /
>   (gdb) target extended-remote | vgdb --multi --vargs -q
>   (gdb) start
> 
> With this GDB work, and once support for the qExecAndArgs packet is
> added to valgrind, then the 'set remote exec-file' line can be dropped
> from those instructions.
> 
> This commit also extends the 'show remote exec-file' command so that
> GDB will display the automatic value that it plans to use.  Here's an
> example of the new output:
> 
>   $ gdb -q /tmp/hello
>   Reading symbols from /tmp/hello...
>   (gdb) set sysroot
>   (gdb) target extended-remote | ./gdbserver/gdbserver --multi --once -
>   Remote debugging using | ./gdbserver/gdbserver --multi --once -
>   Remote debugging using stdio
>   (gdb) show remote exec-file
>   The remote exec-file is unset, using automatic value "/tmp/hello".
> 
> The last line shows the new output.
> 
> Reviewed-By: Eli Zaretskii <eliz@gnu.org>
> ---
>  gdb/NEWS                             |   8 ++
>  gdb/doc/gdb.texinfo                  |   4 +-
>  gdb/remote.c                         | 156 +++++++++++++++++++++++---
>  gdb/testsuite/gdb.server/ext-run.exp | 160 ++++++++++++++++++++++-----
>  4 files changed, 286 insertions(+), 42 deletions(-)

Thanks, the documentation parts are okay.

Reviewed-By: Eli Zaretskii <eliz@gnu.org>