[RFA 1/3] Implement 'set/show exec-file-mismatch'.

Philippe Waroquiers
2019-12-21T14:36:51Z

This option allows to tell GDB to detect and possibly handle mismatched exec-files.

A recurrent problem with GDB is that GDB uses the wrong exec-file
when using the attach/detach commands successively.
Also, in case the user specifies a file on the command line but attaches
to the wrong PID, this error is not made visible and gives a not user
understandable behaviour.

For example:
$ gdb
...
(gdb) atta 2682 ############################################ PID running 'sleepers' executable
Attaching to process 2682
[New LWP 2683]
[New LWP 2684]
[New LWP 2685]
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
0x00007f5ff829f603 in select () at ../sysdeps/unix/syscall-template.S:84
84 ../sysdeps/unix/syscall-template.S: No such file or directory.
(gdb) det
Detaching from program: /home/philippe/valgrind/git/trunk_untouched/gdbserver_tests/sleepers, process 2682
[Inferior 1 (process 2682) detached]
(gdb) atta 31069 ############################################ PID running 'gdb' executable
Attaching to program: /home/philippe/valgrind/git/trunk_untouched/gdbserver_tests/sleepers, process 31069
Reading symbols from /lib64/ld-linux-x86-64.so.2...
Reading symbols from /usr/lib/debug/.build-id/60/6df9c355103e82140d513bc7a25a635591c153.debug...
0x00007f43c23478a0 in ?? ()
(gdb) bt
#0 0x00007f43c23478a0 in ?? ()
#1 0x0000558909e3ad91 in ?? ()
#2 0x0000202962646700 in ?? ()
#3 0x00007ffc69c74e70 in ?? ()
#4 0x000055890c1d2350 in ?? ()
#5 0x0000000000000000 in ?? ()
(gdb)

The second attach has kept the executable of the first attach.
(in this case, 31069 is the PID of a GDB, that has nothing to do
with the first determined 'sleepers' executable).

Similarly, if specifying an executable, but attaching to a wrong pid,
we get:

gdb /home/philippe/valgrind/git/trunk_untouched/gdbserver_tests/sleepers
...
Reading symbols from /home/philippe/valgrind/git/trunk_untouched/gdbserver_tests/sleepers...
(gdb) atta 31069 ############################################ PID running 'gdb' executable
Attaching to program: /home/philippe/valgrind/git/trunk_untouched/gdbserver_tests/sleepers, process 31069
Reading symbols from /lib64/ld-linux-x86-64.so.2...
Reading symbols from /usr/lib/debug/.build-id/60/6df9c355103e82140d513bc7a25a635591c153.debug...
0x00007f43c23478a0 in ?? ()
(gdb) bt
#0 0x00007f43c23478a0 in ?? ()
#1 0x0000558909e3ad91 in ?? ()
#2 0x0000202962646700 in ?? ()
#3 0x00007ffc69c74e70 in ?? ()
#4 0x000055890c1d2350 in ?? ()
#5 0x0000000000000000 in ?? ()
(gdb)

And it is unclear to the user what has happened/what is going wrong.

This patch series implements a new option:
(gdb) apropos exec-file-mismatch
set exec-file-mismatch -- Set exec-file-mismatch handling (reload|warn|off).
show exec-file-mismatch -- Show exec-file-mismatch handling (reload|warn|off).
(gdb) help set exec-file-mismatch
Set exec-file-mismatch handling (reload|warn|off).
Specifies how to handle a mismatch between the current exec-file
and the exec-file automatically determined when attaching to a process:

reload - warn the user, reload the automatically determined exec-file.
warn - warn the user, but do not change the exec-file.
off - do not check for mismatch.
(gdb)

"reload" means: in case of mismatch between the current exec-file
and the automatically determined exec-file of the PID we are attaching to,
give a warning to the user and reload the automatically determined exec-file.

"warn" means: in case of mismatch, just give a warning to the user.

"off" means: do not check for mismatch.

This fixes PR gdb/17626.
There was a previous trial to fix this PR.
See https://sourceware.org/ml/gdb-patches/2015-07/msg00118.html
This trial was however only fixing the problem for the automatically
determined executable files when doing attach.
It was differentiating the 'user specified executable files' ("sticky")
from the executable files automatically found by GDB.
But such user specified sticky executables are in most cases due
to a wrong manipulation by the user, giving unexpected results
such as backtrace showing no function like in the above example.

This patch ensures that whenever a process executable can be
determined, that the user is warned if there is a mismatch.

The same tests as above then give:

(gdb) atta 2682
Attaching to process 2682
[New LWP 2683]
[New LWP 2684]
[New LWP 2685]
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
0x00007f5ff829f603 in select () at ../sysdeps/unix/syscall-template.S:84
84 ../sysdeps/unix/syscall-template.S: No such file or directory.
(gdb) det
Detaching from program: /home/philippe/valgrind/git/trunk_untouched/gdbserver_tests/sleepers, process 2682
[Inferior 1 (process 2682) detached]
(gdb) atta 31069
Attaching to program: /home/philippe/valgrind/git/trunk_untouched/gdbserver_tests/sleepers, process 31069
warning: Mismatch between current exec-file /home/philippe/valgrind/git/trunk_untouched/gdbserver_tests/sleepers
and automatically determined exec-file /bd/home/philippe/gdb/git/build_fixes/gdb/gdb
exec-file-mismatch handling is currently "reload"
Load new symbol table from "/bd/home/philippe/gdb/git/build_fixes/gdb/gdb"? (y or n) y
Reading symbols from /bd/home/philippe/gdb/git/build_fixes/gdb/gdb...
Setting up the environment for debugging gdb.
...
Reading symbols from /usr/lib/debug/.build-id/60/6df9c355103e82140d513bc7a25a635591c153.debug...
0x00007f43c23478a0 in __poll_nocancel () at ../sysdeps/unix/syscall-template.S:84
84 ../sysdeps/unix/syscall-template.S: No such file or directory.
(top-gdb) bt
During symbol reading: incomplete CFI data; unspecified registers (e.g., rax) at 0x7f43c23478ad
During symbol reading: unsupported tag: 'DW_TAG_unspecified_type'
During symbol reading: cannot get low and high bounds for subprogram DIE at 0x12282a7
During symbol reading: Child DIE 0x12288ba and its abstract origin 0x1228b26 have different parents
During symbol reading: DW_AT_call_target target DIE has invalid low pc, for referencing DIE 0x1229540 [in module /bd/home/philippe/gdb/git/build_fixes/gdb/gdb]
#0 0x00007f43c23478a0 in __poll_nocancel () at ../sysdeps/unix/syscall-template.S:84
#1 0x0000558909e3ad91 in poll (__timeout=-1, __nfds=<optimized out>, __fds=<optimized out>) at /usr/include/x86_64-linux-gnu/bits/poll2.h:46
#2 gdb_wait_for_event (block=block@entry=1) at ../../fixes/gdb/event-loop.c:772
#3 0x0000558909e3aef4 in gdb_do_one_event () at ../../fixes/gdb/event-loop.c:347
#4 0x0000558909e3b085 in gdb_do_one_event () at ../../fixes/gdb/common/common-exceptions.h:219
#5 start_event_loop () at ../../fixes/gdb/event-loop.c:371
During symbol reading: Member function "~_Sp_counted_base" (offset 0x1c69bf7) is virtual but the vtable offset is not specified
During symbol reading: Multiple children of DIE 0x1c8f5a0 refer to DIE 0x1c8f0ee as their abstract origin
#6 0x0000558909ed3b78 in captured_command_loop () at ../../fixes/gdb/main.c:331
#7 0x0000558909ed4b6d in captured_main (data=<optimized out>) at ../../fixes/gdb/main.c:1174
#8 gdb_main (args=<optimized out>) at ../../fixes/gdb/main.c:1190
#9 0x0000558909c1e9a8 in main (argc=<optimized out>, argv=<optimized out>) at ../../fixes/gdb/gdb.c:32
(top-gdb)

gdb /home/philippe/valgrind/git/trunk_untouched/gdbserver_tests/sleepers
...
Reading symbols from /home/philippe/valgrind/git/trunk_untouched/gdbserver_tests/sleepers...
(gdb) atta 31069
Attaching to program: /home/philippe/valgrind/git/trunk_untouched/gdbserver_tests/sleepers, process 31069
warning: Mismatch between current exec-file /home/philippe/valgrind/git/trunk_untouched/gdbserver_tests/sleepers
and automatically determined exec-file /bd/home/philippe/gdb/git/build_fixes/gdb/gdb
exec-file-mismatch handling is currently "reload"
Load new symbol table from "/bd/home/philippe/gdb/git/build_fixes/gdb/gdb"? (y or n) y
Reading symbols from /bd/home/philippe/gdb/git/build_fixes/gdb/gdb...
Setting up the environment for debugging gdb.
....

In other words, it now works as intuitively expected by the user.
If ever the user gave the correct executable on the command line,
then attached to the wrong pid, then confirmed loading the wrong executable,
the user can simply fix this by detaching, and attaching to the correct pid,
GDB will then tell again to the user that the exec-file might better
be reloaded.

The default value of "reload" is chosen instead of e.g. "warn" as in most
cases, switching of executable will be the correct action,
and in any case, the user can decide to not load the executable,
as GDB asks a confirmation to the user to load the new executable.

For settings "reload" and "warn", the new function validate_exec_file ()
tries to get the inferior pid exec file and compares it with the current
exec file. In case of mismatch, it warns the user and optionally reload
the executable.
This function is called in the attach_command implementation to cover
most cases of attaching to a running process.
It must also be called in remote.c, as the attach command is not supported
for all types of remote gdbserver.

gdb/ChangeLog
YYYY-MM-DD Philippe Waroquiers <philippe.waroquiers@skynet.be>

* exec.c (xec_file_mismatch_names, exec_file_mismatch_mode)
(show_exec_file_mismatch_command, set_exec_file_mismatch_command)
(validate_exec_file): New variables, enums, functions.
(exec_file_locate_attach, print_section_info): Style the filenames.
(_initialize_exec): Install show_exec_file_mismatch_command and
set_exec_file_mismatch_command.
* gdbcore.h (validate_exec_file): Declare.
* infcmd.c (attach_command): Call validate_exec_file.
* remote.c ( remote_target::remote_add_inferior): Likewise.
---
gdb/exec.c | 144 ++++++++++++++++++++++++++++++++++++++++++++++----
gdb/gdbcore.h | 5 ++
gdb/infcmd.c | 3 ++
gdb/remote.c | 3 ++
4 files changed, 145 insertions(+), 10 deletions(-)

diff --git a/gdb/exec.c b/gdb/exec.c
index efc504eca4..3d36a0ee61 100644
--- a/gdb/exec.c
+++ b/gdb/exec.c
@@ -46,6 +46,7 @@
#include "solist.h"
#include <algorithm>
#include "gdbsupport/pathstuff.h"
+#include "cli/cli-style.h"

void (*deprecated_file_changed_hook) (const char *);

@@ -82,6 +83,50 @@ struct exec_target final : public target_ops

static exec_target exec_ops;

+/* How to handle a mismatch between the current exec file and the exec
+ file determined from target. */
+
+static const char *const exec_file_mismatch_names[]
+ = {"reload", "warn", "off", NULL };
+enum exec_file_mismatch_mode
+ {
+ exec_file_mismatch_reload, exec_file_mismatch_warn, exec_file_mismatch_off
+ };
+static const char *exec_file_mismatch = exec_file_mismatch_names[0];
+static enum exec_file_mismatch_mode exec_file_mismatch_mode
+ = exec_file_mismatch_reload;
+
+/* Show command. */
+static void
+show_exec_file_mismatch_command (struct ui_file *file, int from_tty,
+ struct cmd_list_element *c, const char *value)
+{
+ fprintf_filtered (gdb_stdout,
+ _("exec-file-mismatch handling is currently \"%s\".\n"),
+ exec_file_mismatch_names[exec_file_mismatch_mode]);
+}
+
+/* Set command. Change the setting for range checking. */
+static void
+set_exec_file_mismatch_command (const char *ignore,
+ int from_tty, struct cmd_list_element *c)
+{
+ for (enum exec_file_mismatch_mode mode = exec_file_mismatch_reload;
+ ;
+ mode = static_cast<enum exec_file_mismatch_mode>(1 + (int) mode))
+ {
+ if (strcmp (exec_file_mismatch, exec_file_mismatch_names[mode]) == 0)
+ {
+ exec_file_mismatch_mode = mode;
+ return;
+ }
+ if (mode == exec_file_mismatch_off)
+ internal_error (__FILE__, __LINE__,
+ _("Unrecognized exec-file-mismatch setting: \"%s\""),
+ exec_file_mismatch);
+ }
+}
+
/* Whether to open exec and core files read-only or read-write. */

bool write_files = false;
@@ -191,6 +236,61 @@ try_open_exec_file (const char *exec_file_host, struct inferior *inf,

/* See gdbcore.h. */

+void
+validate_exec_file (int from_tty)
+{
+ /* If user asked to ignore the mismatch, do nothing. */
+ if (exec_file_mismatch_mode == exec_file_mismatch_off)
+ return;
+
+ const char *current_exec_file = get_exec_file (0);
+ struct inferior *inf = current_inferior ();
+ /* Try to determine a filename from the process itself. */
+ const char *pid_exec_file = target_pid_to_exec_file (inf->pid);
+
+ /* If wee cannot validate the exec file, return. */
+ if (current_exec_file == NULL || pid_exec_file == NULL)
+ return;
+
+ std::string exec_file_target (pid_exec_file);
+
+ /* In case the exec file is not local, exec_file_target has to point at
+ the target file system. */
+ if (is_target_filename (current_exec_file) && !target_filesystem_is_local ())
+ exec_file_target = TARGET_SYSROOT_PREFIX + exec_file_target;
+
+ if (exec_file_target != current_exec_file)
+ {
+ warning
+ (_("Mismatch between current exec-file %ps\n"
+ "and automatically determined exec-file %ps\n"
+ "exec-file-mismatch handling is currently \"%s\""),
+ styled_string (file_name_style.style (), current_exec_file),
+ styled_string (file_name_style.style (), exec_file_target.c_str ()),
+ exec_file_mismatch_names[exec_file_mismatch_mode]);
+ if (exec_file_mismatch_mode == exec_file_mismatch_reload)
+ {
+ symfile_add_flags add_flags = SYMFILE_MAINLINE;
+ if (from_tty)
+ add_flags |= SYMFILE_VERBOSE;
+ try
+ {
+ symbol_file_add_main (exec_file_target.c_str (), add_flags);
+ exec_file_attach (exec_file_target.c_str (), from_tty);
+ }
+ catch (gdb_exception_error &err)
+ {
+ warning (_("reloading %ps %s"),
+ styled_string (file_name_style.style (),
+ exec_file_target.c_str ()),
+ err.message != NULL ? err.what () : "error");
+ }
+ }
+ }
+}
+
+/* See gdbcore.h. */
+
void
exec_file_locate_attach (int pid, int defer_bp_reset, int from_tty)
{
@@ -331,8 +431,9 @@ exec_file_attach (const char *filename, int from_tty)

if (!exec_bfd)
{
- error (_("\"%s\": could not open as an executable file: %s."),
- scratch_pathname, bfd_errmsg (bfd_get_error ()));
+ error (_("\"%ps\": could not open as an executable file: %s."),
+ styled_string (file_name_style.style (), scratch_pathname),
+ bfd_errmsg (bfd_get_error ()));
}

/* gdb_realpath_keepfile resolves symlinks on the local
@@ -348,8 +449,8 @@ exec_file_attach (const char *filename, int from_tty)
/* Make sure to close exec_bfd, or else "run" might try to use
it. */
exec_close ();
- error (_("\"%s\": not in executable format: %s"),
- scratch_pathname,
+ error (_("\"%ps\": not in executable format: %s"),
+ styled_string (file_name_style.style (), scratch_pathname),
gdb_bfd_errmsg (bfd_get_error (), matching).c_str ());
}

@@ -358,8 +459,9 @@ exec_file_attach (const char *filename, int from_tty)
/* Make sure to close exec_bfd, or else "run" might try to use
it. */
exec_close ();
- error (_("\"%s\": can't find the file sections: %s"),
- scratch_pathname, bfd_errmsg (bfd_get_error ()));
+ error (_("\"%ps\": can't find the file sections: %s"),
+ styled_string (file_name_style.style (), scratch_pathname),
+ bfd_errmsg (bfd_get_error ()));
}

exec_bfd_mtime = bfd_get_mtime (exec_bfd);
@@ -879,7 +981,9 @@ print_section_info (struct target_section_table *t, bfd *abfd)
/* FIXME: 16 is not wide enough when gdbarch_addr_bit > 64. */
int wid = gdbarch_addr_bit (gdbarch) <= 32 ? 8 : 16;

- printf_filtered ("\t`%s', ", bfd_get_filename (abfd));
+ printf_filtered ("\t`%ps', ",
+ styled_string (file_name_style.style (),
+ bfd_get_filename (abfd)));
wrap_here (" ");
printf_filtered (_("file type %s.\n"), bfd_get_target (abfd));
if (abfd == exec_bfd)
@@ -906,8 +1010,9 @@ print_section_info (struct target_section_table *t, bfd *abfd)
}
}
if (p == t->sections_end)
- warning (_("Cannot find section for the entry point of %s."),
- bfd_get_filename (abfd));
+ warning (_("Cannot find section for the entry point of %ps."),
+ styled_string (file_name_style.style (),
+ bfd_get_filename (abfd)));

entry_point = gdbarch_addr_bits_remove (gdbarch,
bfd_get_start_address (abfd)
@@ -934,7 +1039,9 @@ print_section_info (struct target_section_table *t, bfd *abfd)
hex_string_custom (psect->filepos, 8));
printf_filtered (" is %s", bfd_section_name (psect));
if (pbfd != abfd)
- printf_filtered (" in %s", bfd_get_filename (pbfd));
+ printf_filtered (" in %ps",
+ styled_string (file_name_style.style (),
+ bfd_get_filename (pbfd)));
printf_filtered ("\n");
}
}
@@ -1070,5 +1177,22 @@ Show writing into executable and core files."), NULL,
show_write_files,
&setlist, &showlist);

+ add_setshow_enum_cmd ("exec-file-mismatch", class_support,
+ exec_file_mismatch_names,
+ &exec_file_mismatch,
+ _("\
+Set exec-file-mismatch handling (reload|warn|off)."),
+ _("\
+Show exec-file-mismatch handling (reload|warn|off)."),
+ _("\
+Specifies how to handle a mismatch between the current exec-file\n\
+and the exec-file automatically determined when attaching to a process:\n\n\
+ reload - warn the user, reload the automatically determined exec-file.\n\
+ warn - warn the user, but do not change the exec-file.\n\
+ off - do not check for mismatch."),
+ set_exec_file_mismatch_command,
+ show_exec_file_mismatch_command,
+ &setlist, &showlist);
+
add_target (exec_target_info, exec_target_open, filename_completer);
}
diff --git a/gdb/gdbcore.h b/gdb/gdbcore.h
index cac91c097b..5ff5e9e5ab 100644
--- a/gdb/gdbcore.h
+++ b/gdb/gdbcore.h
@@ -157,6 +157,11 @@ extern void exec_file_locate_attach (int pid, int defer_bp_reset, int from_tty);

extern void validate_files (void);

+/* Give the user a message if the current exec file does not match the exec
+ file determined from the target. In case of mismatch, ask the user
+ if the exec file determined from target must be loaded. */
+extern void validate_exec_file (int from_tty);
+
/* The current default bfd target. */

extern char *gnutarget;
diff --git a/gdb/infcmd.c b/gdb/infcmd.c
index af66eaffd8..df4478a26a 100644
--- a/gdb/infcmd.c
+++ b/gdb/infcmd.c
@@ -2782,6 +2782,9 @@ attach_command (const char *args, int from_tty)
target_stop (ptid_t (inferior_ptid.pid ()));
}

+ /* Check for exec file mismatch, and let the user solve it. */
+ validate_exec_file (from_tty);
+
mode = async_exec ? ATTACH_POST_WAIT_RESUME : ATTACH_POST_WAIT_STOP;

/* Some system don't generate traps when attaching to inferior.
diff --git a/gdb/remote.c b/gdb/remote.c
index 3c544502a8..6894a2b074 100644
--- a/gdb/remote.c
+++ b/gdb/remote.c
@@ -2378,6 +2378,9 @@ remote_target::remote_add_inferior (bool fake_pid_p, int pid, int attached,
if (try_open_exec && get_exec_file (0) == NULL)
exec_file_locate_attach (pid, 0, 1);

+ /* Check for exec file mismatch, and let the user solve it. */
+ validate_exec_file (1);
+
return inf;
}

--
2.20.1