[9/9] gdb: use reopen_exec_file from reread_symbols

Message ID beb69bea3ed292317afc7822feaf98e69c5022a6.1694858967.git.aburgess@redhat.com
State New
Series Add executable_changed event to Python API |


Context Check Description
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Commit Message

Andrew Burgess Sept. 16, 2023, 10:18 a.m. UTC
  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

  #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

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.
 gdb/symfile.c                             | 18 +++++-------------
 gdb/testsuite/gdb.python/py-exec-file.exp |  5 -----
 2 files changed, 5 insertions(+), 18 deletions(-)


Tom Tromey Sept. 19, 2023, 2:08 p.m. UTC | #1
>>>>> "Andrew" == Andrew Burgess via Gdb-patches <gdb-patches@sourceware.org> writes:
Andrew> +  reopen_exec_file ();

This addition could probably use a comment explaining why it is needed.

Andrew> -      new_modtime = new_statbuf.st_mtime;
Andrew> +      long new_modtime = new_statbuf.st_mtime;

Might as well change this to time_t now.

I don't really understand how reread_symbols interacts with target:
files.  It seems like this is just broken.

At AdaCore we carry a patch that changes this code to use bfd_stat.
According to internal notes, this was pushed:


... but I don't see it in gdb.  Maybe we never resolved the 'stat' issue
in gnulib?

Anyway, the reason I bring this up is that reopen_exec_file calls
bfd_cache_close_all -- but then the loop in reread_symbols, in the
bfd_stat case, will reopen the files (BFD uses fstat).  This seems

I don't think gdb has a very clear idea of when bfd_cache_close_all
ought to be called.  It would be good to clear this up.  I'm not very
clear on it myself.  Maybe it is to avoid ETXTBUSY errors -- in which
case it seems like it should be called just before starting the
inferior.  But, ISTR some error on Windows as well, though I don't know
exactly what... so maybe the files need to be guaranteed-closed in other
situations as well.



diff --git a/gdb/symfile.c b/gdb/symfile.c
index 43fd45c4050..fac8ec19a22 100644
--- a/gdb/symfile.c
+++ b/gdb/symfile.c
@@ -2457,11 +2457,10 @@  remove_symbol_file_command (const char *args, int from_tty)
 reread_symbols (int from_tty)
-  long new_modtime;
-  struct stat new_statbuf;
-  int res;
   std::vector<struct objfile *> new_objfiles;
+  reopen_exec_file ();
   for (objfile *objfile : current_program_space->objfiles ())
       if (objfile->obfd.get () == NULL)
@@ -2475,6 +2474,8 @@  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);
@@ -2486,7 +2487,7 @@  reread_symbols (int from_tty)
 		      objfile_name (objfile));
-      new_modtime = new_statbuf.st_mtime;
+      long new_modtime = new_statbuf.st_mtime;
       if (new_modtime != objfile->mtime)
 	  gdb_printf (_("`%ps' has changed; re-reading symbols.\n"),
@@ -2508,15 +2509,6 @@  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
diff --git a/gdb/testsuite/gdb.python/py-exec-file.exp b/gdb/testsuite/gdb.python/py-exec-file.exp
index 5ad3cd7e50f..7aa19a867d7 100644
--- a/gdb/testsuite/gdb.python/py-exec-file.exp
+++ b/gdb/testsuite/gdb.python/py-exec-file.exp
@@ -190,11 +190,6 @@  with_test_prefix "exec changes on disk" {
-    # 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"