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* [binutils-gdb] gdb: remove manual frame_info reinflation code in backtrace_command_1
@ 2022-11-10 16:34 Simon Marchi
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From: Simon Marchi @ 2022-11-10 16:34 UTC (permalink / raw)
To: gdb-cvs
https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=73cafdbd1ddd6ebfa21d737e3b69ae5aafd70c23
commit 73cafdbd1ddd6ebfa21d737e3b69ae5aafd70c23
Author: Simon Marchi <simon.marchi@efficios.com>
Date: Mon Oct 24 15:57:26 2022 -0400
gdb: remove manual frame_info reinflation code in backtrace_command_1
With the following patch applied (gdb: use frame_id_p instead of
comparing to null_frame_id in frame_info_ptr::reinflate), I would get:
$ ./gdb -q -nx --data-directory=data-directory testsuite/outputs/gdb.base/bt-selected-frame/bt-selected-frame -ex "b breakpt" -ex r -ex "bt full"
Reading symbols from testsuite/outputs/gdb.base/bt-selected-frame/bt-selected-frame...
Breakpoint 1 at 0x1131: file /home/smarchi/src/binutils-gdb/gdb/testsuite/gdb.base/bt-selected-frame.c, line 22.
Starting program: /home/smarchi/build/binutils-gdb/gdb/testsuite/outputs/gdb.base/bt-selected-frame/bt-selected-frame
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
Breakpoint 1, breakpt () at /home/smarchi/src/binutils-gdb/gdb/testsuite/gdb.base/bt-selected-frame.c:22
22 }
#0 breakpt () at /home/smarchi/src/binutils-gdb/gdb/testsuite/gdb.base/bt-selected-frame.c:22
No locals.
/home/smarchi/src/binutils-gdb/gdb/frame-info.c:42: internal-error: reinflate: Assertion `frame_id_p (m_cached_id)' failed.
This is because the code in backtrace_command_1 to manually reinflate
`fi` steps overs frame_info_ptr's toes.
When calling
fi.prepare_reinflate ();
`fi` gets properly filled with the cached frame id. But when this
happens:
fi = frame_find_by_id (frame_id);
`fi` gets replaced by a brand new frame_info_ptr that doesn't have a
cached frame id. Then this is called without a cached frame id:
fi.reinflate ();
That doesn't cause any problem currently, since
- the gdb_assert in the reinflate method doesn't actually do anything
(the following patch fixes that)
- `fi.m_ptr` will always be non-nullptr, since we just got it from
frame_find_by_id, so reinflate will not do anything, it won't try to
use m_cached_id
Fix that by removing the code to manually re-fetch the frame. That
should be taken care of by frame_info_ptr::reinflate.
Note that the old code checked if we successfully re-inflated the frame
or not, and if not it did emit a warning. The equivalent in
frame_info_ptr::reinflate asserts that the frame has been successfully
re-inflated. It's not clear if / when this can happen, but if it can
happen, we'll need to find a solution to this problem globally
(everywhere a frame_info_ptr can be re-inflated), not just here. So I
propose to leave it like this, until it does become a problem.
Reviewed-By: Bruno Larsen <blarsen@redhat.com>
Change-Id: I07b783d94e2853e0a2d058fe7deaf04eddf24835
Diff:
---
gdb/stack.c | 15 +--------------
1 file changed, 1 insertion(+), 14 deletions(-)
diff --git a/gdb/stack.c b/gdb/stack.c
index 4e2342c2a8d..5f29566fcfe 100644
--- a/gdb/stack.c
+++ b/gdb/stack.c
@@ -2082,20 +2082,7 @@ backtrace_command_1 (const frame_print_options &fp_opts,
print_frame_info (fp_opts, fi, 1, LOCATION, 1, 0);
if ((flags & PRINT_LOCALS) != 0)
- {
- struct frame_id frame_id = get_frame_id (fi);
-
- print_frame_local_vars (fi, false, NULL, NULL, 1, gdb_stdout);
-
- /* print_frame_local_vars invalidates FI. */
- fi = frame_find_by_id (frame_id);
- if (fi == NULL)
- {
- trailing = NULL;
- warning (_("Unable to restore previously selected frame."));
- break;
- }
- }
+ print_frame_local_vars (fi, false, NULL, NULL, 1, gdb_stdout);
/* Save the last frame to check for error conditions. */
fi.reinflate ();
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2022-11-10 16:34 [binutils-gdb] gdb: remove manual frame_info reinflation code in backtrace_command_1 Simon Marchi
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