[binutils-gdb] gdb: call target_follow_exec when "set follow-exec-mode" is "same"
Simon Marchi
simark@sourceware.org
Thu May 13 19:29:58 GMT 2021
https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=2af87c859fe450d4a3a841cf19637a91d53c9486
commit 2af87c859fe450d4a3a841cf19637a91d53c9486
Author: Simon Marchi <simon.marchi@efficios.com>
Date: Thu May 13 15:27:55 2021 -0400
gdb: call target_follow_exec when "set follow-exec-mode" is "same"
target_follow_exec is currently only called in the "follow-exec-mode ==
new" branch of follow_exec, not the "follow-exec-mode == same" branch.
I think it would make sense to call it regardless of the mode to let
targets do some necessary handling.
This is needed in the context of rocm-gdb [1], where a target is pushed
on top of the linux-nat target. On exec, it needs to do some
bookkeeping, close some file descriptors / handles that were related to
the process pre-exec and open some new ones for the process post-exec.
However, by looking at the only in-tree implementation of
target_ops::follow_exec, remote_target::follow_exec, I found that it
would be useful for the extended-remote target too, to align its
behavior with native debugging (although I think that behavior is not
very user-friendly, see PR 27745 [2]).
Using two programs, one (let's call it "execer") that execs the other
(let's call it "execee"), with native:
$ ./gdb -q -nx --data-directory=data-directory ./execer
Reading symbols from ./execer...
(gdb) r
Starting program: /home/simark/build/binutils-gdb/gdb/execer
I am execer
process 1495622 is executing new program: /home/simark/build/binutils-gdb/gdb/execee
I am execee
[Inferior 1 (process 1495622) exited normally]
(gdb) r
Starting program: /home/simark/build/binutils-gdb/gdb/execee
I am execee
[Inferior 1 (process 1495626) exited normally]
And now with gdbserver (some irrelevant output lines removed for brevity):
$ ./gdbserver --once --multi :1234
...
$ ./gdb -q -nx --data-directory=data-directory ./execer -ex "set remote exec-file /home/simark/build/binutils-gdb/gdb/execer" -ex "tar ext :1234"
Reading symbols from ./execer...
Remote debugging using :1234
(gdb) r
Starting program: /home/simark/build/binutils-gdb/gdb/execer
process 1495724 is executing new program: /home/simark/build/binutils-gdb/gdb/execee
[Inferior 1 (process 1495724) exited normally]
(gdb) r
`target:/home/simark/build/binutils-gdb/gdb/execee' has disappeared; keeping its symbols.
Starting program: target:/home/simark/build/binutils-gdb/gdb/execee
warning: Build ID mismatch between current exec-file target:/home/simark/build/binutils-gdb/gdb/execee
and automatically determined exec-file target:/home/simark/build/binutils-gdb/gdb/execer
exec-file-mismatch handling is currently "ask"
Reading /home/simark/build/binutils-gdb/gdb/execer from remote target...
Load new symbol table from "target:/home/simark/build/binutils-gdb/gdb/execer"? (y or n)
When handling the exec, GDB updates the exec-file of the inferior to be
the execee. This means that a subsequent "run" will run the execee, not
the original executable (execer).
remote_target::follow_exec is meant to update the "remote exec-file",
which is the file on the remote system that will be executed if you
"run" the inferior, to the execee as well. However, this is not called
when follow-exec-mode is same, because target_follow_exec is not called
in this branch. As a result, GDB thinks the inferior is executing
execee but the remote side is really executing execer, hence the
mismatch message.
By calling target_follow_exec in the "same" branch of the follow_exec
function, we ensure that everybody agrees, and we get the same behavior
with the extended-remote target as we get with the native target, the
execee is executed on the second run:
$ ./gdbserver --once --multi :1234
...
$ ./gdb -q -nx --data-directory=data-directory ./execer -ex "set remote exec-file /home/simark/build/binutils-gdb/gdb/execer" -ex "tar ext :1234"
Reading symbols from ./execer...
Remote debugging using :1234
(gdb) r
Starting program: /home/simark/build/binutils-gdb/gdb/execer
process 1501445 is executing new program: /home/simark/build/binutils-gdb/gdb/execee
[Inferior 1 (process 1501445) exited normally]
(gdb) r
`target:/home/simark/build/binutils-gdb/gdb/execee' has disappeared; keeping its symbols.
Starting program: target:/home/simark/build/binutils-gdb/gdb/execee
[Inferior 1 (process 1501447) exited normally]
(gdb)
This scenario is tested in gdb.base/foll-exec-mode.exp, and in fact this
patch fixes the test for me when using
--target_board=native-extended-gdbserver.
gdb/ChangeLog:
* infrun.c (follow_exec): Call target_follow_fork when
follow-exec-mode is same.
* target.h (target_follow_fork): Improve doc.
[1] https://github.com/ROCm-Developer-Tools/ROCgdb
[2] https://sourceware.org/bugzilla/show_bug.cgi?id=27745
Change-Id: I4ee84a875e39bf3f8eaf3e6789a4bfe23a2a430e
Diff:
---
gdb/ChangeLog | 6 ++++++
gdb/infrun.c | 1 +
gdb/target.h | 7 +++++--
3 files changed, 12 insertions(+), 2 deletions(-)
diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index de66783dd26..f0ae77e1218 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,9 @@
+2021-05-13 Simon Marchi <simon.marchi@efficios.com>
+
+ * infrun.c (follow_exec): Call target_follow_fork when
+ follow-exec-mode is same.
+ * target.h (target_follow_fork): Improve doc.
+
2021-05-13 Simon Marchi <simon.marchi@polymtl.ca>
* cli/cli-decode.h (struct cmd_list_element) <pre_show_hook>:
diff --git a/gdb/infrun.c b/gdb/infrun.c
index 90bab8d984f..3e386aa587c 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -1198,6 +1198,7 @@ follow_exec (ptid_t ptid, const char *exec_file_target)
around (its description is later cleared/refetched on
restart). */
target_clear_description ();
+ target_follow_exec (inf, exec_file_target);
}
gdb_assert (current_program_space == inf->pspace);
diff --git a/gdb/target.h b/gdb/target.h
index 48bf734279a..b80cf88db81 100644
--- a/gdb/target.h
+++ b/gdb/target.h
@@ -1714,8 +1714,11 @@ extern int target_remove_vfork_catchpoint (int pid);
void target_follow_fork (bool follow_child, bool detach_fork);
-/* Handle the target-specific bookkeeping required when the inferior
- makes an exec call. INF is the exec'd inferior. */
+/* Handle the target-specific bookkeeping required when the inferior makes an
+ exec call. The current inferior is the inferior that has executed the exec
+ call. INF is the inferior in which execution continues post-exec. It is the
+ same inferior as the current one if "follow-exec-mode" is "same" but is a new
+ one if "follow-exec-mode" is "new". */
void target_follow_exec (struct inferior *inf, const char *execd_pathname);
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