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0850800ff0
This commit works around a problem introduced by commit:
commit e58beedf2c
Date: Tue Jan 23 16:00:59 2024 +0000
gdb: attach to a process when the executable has been deleted
The above commit extended GDB for Linux, so that, of the executable
for a process had been deleted, GDB would instead try to use
/proc/PID/exe as the executable.
This worked by updating linux_proc_pid_to_exec_file to introduce the
/proc/PID/exe fallback. However, the result of
linux_proc_pid_to_exec_file is then passed to exec_file_find to
actually find the executable, and exec_file_find, will take into
account the sysroot. In addition, if GDB is attaching to a process in
a different MNT and/or PID namespace then the executable lookup is
done within that namespace.
This all means two things:
1. Just because linux_proc_pid_to_exec_file cannot see the
executable doesn't mean that GDB is actually going to fail to
find the executable, and
2. returning /proc/PID/exe isn't useful if we know GDB is then going
to look for this within a sysroot, or within some other
namespace (where PIDs might be different).
There was an initial attempt to fix this issue here:
https://inbox.sourceware.org/gdb-patches/20250511141517.2455092-4-kilger@sec.in.tum.de/
This proposal addresses the issue in PR gdb/32955, which is all about
the namespace side of the problem. The fix in this original proposal
is to check the MNT namespace inside linux_proc_pid_to_exec_file, and
for the namespace problem this is fine. But we should also consider
the sysroot problem.
And for the sysroot problem, the fix cannot fully live inside
linux_proc_pid_to_exec_file, as linux_proc_pid_to_exec_file is shared
between GDB and gdbserver, and gdbserver has no sysroot.
And so, I propose a slightly bigger change.
Now, linux_proc_pid_to_exec_file takes a flag which indicates if
GDB (or gdbserver) will look for the inferior executable in the
local file system, where local means the same file system as GDB (or
gdbserver) is running in.
This local file system check is true if:
1. The MNT namespace of the inferior is the same as for GDB, and
2. for GDB only, the sysroot must either be empty, or 'target:'.
If the local file system check is false then GDB (or gdbserver) is
going to look elsewhere for the inferior executable, and so, falling
back to /proc/PID/exe should not be done, as GDB will end up looking
for this file in the sysroot, or within the alternative MNT
namespace (which in also likely to be a different PID namespace).
Now this is all a bit of a shame really. It would be nice if
linux_proc_pid_to_exec_file could return /proc/PID/exe in such a way
that exec_file_find would know that the file should NOT be looked for
in the sysroot, or in the alternative namespace. But fixing that
problem would be a much bigger change, so for now lets just disable
the /proc/PID/exe fallback for cases where it might not work.
For testing, the sysroot case is now tested.
I don't believe we have any alternative namespace testing. It would
certainly be interesting to add some, but I'm not proposing any with
this patch, so the code for checking the MNT namespace has been tested
manually by me, but isn't covered by a new test I'm adding here.
Author of the original fix is listed as co-author here. Credit for
identifying the original problem, and proposing a solution belongs to
them.
Co-Authored-By: Fabian Kilger <kilger@sec.in.tum.de>
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=32955
110 lines
4.1 KiB
C++
110 lines
4.1 KiB
C++
/* Linux-specific PROCFS manipulation routines.
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Copyright (C) 2011-2025 Free Software Foundation, Inc.
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This file is part of GDB.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>. */
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#ifndef GDB_NAT_LINUX_PROCFS_H
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#define GDB_NAT_LINUX_PROCFS_H
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#include <unistd.h>
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/* Return the TGID of LWPID from /proc/pid/status. Returns -1 if not
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found. Failure to open the /proc file results in a warning. */
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extern int linux_proc_get_tgid (pid_t lwpid);
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/* Return the TracerPid of LWPID from /proc/pid/status. Returns -1 if
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not found. Does not warn on failure to open the /proc file. */
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extern pid_t linux_proc_get_tracerpid_nowarn (pid_t lwpid);
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/* Detect `T (stopped)' in `/proc/PID/status'.
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Other states including `T (tracing stop)' are reported as false. */
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extern int linux_proc_pid_is_stopped (pid_t pid);
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extern int linux_proc_pid_is_trace_stopped_nowarn (pid_t pid);
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/* Return non-zero if PID is a zombie. Failure to open the
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/proc/pid/status file results in a warning. */
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extern int linux_proc_pid_is_zombie (pid_t pid);
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/* Return non-zero if PID is a zombie. Does not warn on failure to
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open the /proc file. */
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extern int linux_proc_pid_is_zombie_nowarn (pid_t pid);
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/* Return non-zero if /proc/PID/status indicates that PID is gone
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(i.e., in Z/Zombie or X/Dead state). Failure to open the /proc
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file is assumed to indicate the thread is gone. */
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extern int linux_proc_pid_is_gone (pid_t pid);
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/* Index of fields of interest in /proc/PID/stat, from procfs(5) man page. */
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#define LINUX_PROC_STAT_STATE 3
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#define LINUX_PROC_STAT_STARTTIME 22
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#define LINUX_PROC_STAT_PROCESSOR 39
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/* Returns FIELD (as numbered in procfs(5) man page) of
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/proc/PID/task/LWP/stat file. */
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extern std::optional<std::string> linux_proc_get_stat_field (ptid_t ptid,
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int field);
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/* Return a string giving the thread's name or NULL if the
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information is unavailable. The returned value points to a statically
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allocated buffer. The value therefore becomes invalid at the next
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linux_proc_tid_get_name call. */
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extern const char *linux_proc_tid_get_name (ptid_t ptid);
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/* Callback function for linux_proc_attach_tgid_threads. If the PTID
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thread is not yet known, try to attach to it and return true,
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otherwise return false. */
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typedef int (*linux_proc_attach_lwp_func) (ptid_t ptid);
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/* If PID is a tgid, scan the /proc/PID/task/ directory for existing
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threads, and call FUNC for each thread found. */
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extern void linux_proc_attach_tgid_threads (pid_t pid,
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linux_proc_attach_lwp_func func);
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/* Return true if the /proc/PID/task/ directory exists. */
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extern int linux_proc_task_list_dir_exists (pid_t pid);
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/* Return the full absolute name of the executable file that was run
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to create the process PID. The returned value persists until this
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function is next called.
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LOCAL_FS should be true if the file returned from the function will
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be searched for in the same filesystem as GDB itself is running.
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In practice, this means LOCAL_FS should be true if PID and GDB are
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running in the same MNT namespace and GDB's sysroot is either the
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empty string, or is 'target:'.
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When used from gdbserver, where there is no sysroot, the only check
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that matters is that PID and gdbserver are running in the same MNT
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namespace. */
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extern const char *linux_proc_pid_to_exec_file (int pid, bool local_fs);
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/* Display possible problems on this system. Display them only once
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per GDB execution. */
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extern void linux_proc_init_warnings ();
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#endif /* GDB_NAT_LINUX_PROCFS_H */
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