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From: Simon Marchi <simark@sourceware.org> To: gdb-cvs@sourceware.org Subject: [binutils-gdb] gdb: remove manual frame_info reinflation code in backtrace_command_1 Date: Thu, 10 Nov 2022 16:34:05 +0000 (GMT) [thread overview] Message-ID: <20221110163405.ED7373858439@sourceware.org> (raw) 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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