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gdb: use reopen_exec_file from reread_symbols
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This commit fixes an issue that was discovered while writing the tests
for the previous commit.

I noticed that, when GDB restarts an inferior, the executable_changed
event would trigger twice.  The first notification would originate
from:

  #0  exec_file_attach (filename=0x4046680 "/tmp/hello.x", from_tty=0) at ../../src/gdb/exec.c:513
  #1  0x00000000006f3adb in reopen_exec_file () at ../../src/gdb/corefile.c:122
  #2  0x0000000000e6a3f2 in generic_mourn_inferior () at ../../src/gdb/target.c:3682
  #3  0x0000000000995121 in inf_child_target::mourn_inferior (this=0x2fe95c0 <the_amd64_linux_nat_target>) at ../../src/gdb/inf-child.c:192
  #4  0x0000000000995cff in inf_ptrace_target::mourn_inferior (this=0x2fe95c0 <the_amd64_linux_nat_target>) at ../../src/gdb/inf-ptrace.c:125
  #5  0x0000000000a32472 in linux_nat_target::mourn_inferior (this=0x2fe95c0 <the_amd64_linux_nat_target>) at ../../src/gdb/linux-nat.c:3609
  #6  0x0000000000e68a40 in target_mourn_inferior (ptid=...) at ../../src/gdb/target.c:2761
  #7  0x0000000000a323ec in linux_nat_target::kill (this=0x2fe95c0 <the_amd64_linux_nat_target>) at ../../src/gdb/linux-nat.c:3593
  #8  0x0000000000e64d1c in target_kill () at ../../src/gdb/target.c:924
  #9  0x00000000009a19bc in kill_if_already_running (from_tty=1) at ../../src/gdb/infcmd.c:328
  #10 0x00000000009a1a6f in run_command_1 (args=0x0, from_tty=1, run_how=RUN_STOP_AT_MAIN) at ../../src/gdb/infcmd.c:381
  #11 0x00000000009a20a5 in start_command (args=0x0, from_tty=1) at ../../src/gdb/infcmd.c:527
  #12 0x000000000068dc5d in do_simple_func (args=0x0, from_tty=1, c=0x35c7200) at ../../src/gdb/cli/cli-decode.c:95

While the second originates from:

  #0  exec_file_attach (filename=0x3d7a1d0 "/tmp/hello.x", from_tty=0) at ../../src/gdb/exec.c:513
  #1  0x0000000000dfe525 in reread_symbols (from_tty=1) at ../../src/gdb/symfile.c:2517
  #2  0x00000000009a1a98 in run_command_1 (args=0x0, from_tty=1, run_how=RUN_STOP_AT_MAIN) at ../../src/gdb/infcmd.c:398
  #3  0x00000000009a20a5 in start_command (args=0x0, from_tty=1) at ../../src/gdb/infcmd.c:527
  #4  0x000000000068dc5d in do_simple_func (args=0x0, from_tty=1, c=0x35c7200) at ../../src/gdb/cli/cli-decode.c:95

In the first case the call to exec_file_attach first passes through
reopen_exec_file.  The reopen_exec_file performs a modification time
check on the executable file, and only calls exec_file_attach if the
executable has changed on disk since it was last loaded.

However, in the second case things work a little differently.  In this
case GDB is really trying to reread the debug symbol.  As such, we
iterate over the objfiles list, and for each of those we check the
modification time, if the file on disk has changed then we reload the
debug symbols from that file.

However, there is an additional check, if the objfile has the same
name as the executable then we will call exec_file_attach, but we do
so without checking the cached modification time that indicates when
the executable was last reloaded, as a result, we reload the
executable twice.

In this commit I propose that reread_symbols be changed to
unconditionally call reopen_exec_file before performing the objfile
iteration.  This will ensure that, if the executable has changed, then
the executable will be reloaded, however, if the executable has
already been recently reloaded, we will not reload it for a second
time.

After handling the executable, GDB can then iterate over the objfiles
list and reload them in the normal way.

With this done I now see the executable reloaded only once when GDB
restarts an inferior, which means I can remove the kfail that I added
to the gdb.python/py-exec-file.exp test in the previous commit.

Approved-By: Tom Tromey <tom@tromey.com>
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@T-J-Teru
T-J-Teru committed Sep 28, 2023
1 parent 42f297a commit c7bdb38
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Showing 2 changed files with 10 additions and 18 deletions.
23 changes: 10 additions & 13 deletions gdb/symfile.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -2457,11 +2457,15 @@ remove_symbol_file_command (const char *args, int from_tty)
void
reread_symbols (int from_tty)
{
long new_modtime;
struct stat new_statbuf;
int res;
std::vector<struct objfile *> new_objfiles;

/* Check to see if the executable has changed, and if so reopen it. The
executable might not be in the list of objfiles (if the user set
different values for 'exec-file' and 'symbol-file'), and even if it
is, then we use a separate timestamp (within the program_space) to
indicate when the executable was last reloaded. */
reopen_exec_file ();

for (objfile *objfile : current_program_space->objfiles ())
{
if (objfile->obfd.get () == NULL)
Expand All @@ -2475,6 +2479,8 @@ reread_symbols (int from_tty)
`ar', often called a `static library' on most systems, though
a `shared library' on AIX is also an archive), then you should
stat on the archive name, not member name. */
int res;
struct stat new_statbuf;
if (objfile->obfd->my_archive)
res = stat (bfd_get_filename (objfile->obfd->my_archive), &new_statbuf);
else
Expand All @@ -2486,7 +2492,7 @@ reread_symbols (int from_tty)
objfile_name (objfile));
continue;
}
new_modtime = new_statbuf.st_mtime;
time_t new_modtime = new_statbuf.st_mtime;
if (new_modtime != objfile->mtime)
{
gdb_printf (_("`%ps' has changed; re-reading symbols.\n"),
Expand All @@ -2508,15 +2514,6 @@ reread_symbols (int from_tty)
/* We need to do this whenever any symbols go away. */
clear_symtab_users_cleanup defer_clear_users (0);

if (current_program_space->exec_bfd () != NULL
&& filename_cmp (bfd_get_filename (objfile->obfd.get ()),
bfd_get_filename (current_program_space->exec_bfd ())) == 0)
{
/* Reload EXEC_BFD without asking anything. */

exec_file_attach (bfd_get_filename (objfile->obfd.get ()), 0);
}

/* Keep the calls order approx. the same as in free_objfile. */

/* Free the separate debug objfiles. It will be
Expand Down
5 changes: 0 additions & 5 deletions gdb/testsuite/gdb.python/py-exec-file.exp
View file
Original file line number Diff line number Diff line change
Expand Up @@ -190,11 +190,6 @@ with_test_prefix "exec changes on disk" {

runto_main

# There is currently an issue where the executable_changed event
# will trigger twice during an inferior restart. This should be
# fixed in the next commit, at which point this kfail can be
# removed.
setup_kfail "????" *-*-*
check_exec_change [string_to_regexp $binfile1] True \
"check executable_changed state after exec changed on disk"
}

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