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On 04/13/2016 10:00 AM, Pedro Alves wrote:
On 04/12/2016 08:24 PM, Luis Machado wrote:When we attempt to debug a process using GDBserver in standard remote mode without a symbol file on GDB's end, we may run into an issue where GDB cuts the connection attempt short due to an error. The error is caused by not being able to open a symbol file, like so: -- (gdb) set sysroot (gdb) tar rem :2345 Remote debugging using :2345 /proc/23769/exe: Permission denied. (gdb) i r The program has no registers now. (gdb) It should've been like this: (gdb) set sysroot (gdb) tar rem :2345 Remote debugging using :2345 0xf7ddb2d0 in ?? ()The warning output is missing here, right?
It is, because i did not update it after the patch. :-) Should be fixed in v3.
(gdb) i r eax 0x0 0 ecx 0x0 0 edx 0x0 0 ebx 0x0 0 esp 0xffffdfa0 0xffffdfa0 ebp 0x0 0x0 esi 0x0 0 edi 0x0 0 eip 0xf7ddb2d0 0xf7ddb2d0 eflags 0x200 [ IF ] cs 0x33 51 ss 0x2b 43 ds 0x0 0 es 0x0 0 fs 0x0 0 gs 0x0 0 (gdb)void @@ -142,6 +161,7 @@ exec_file_locate_attach (int pid, int from_tty) { char *exec_file, *full_exec_path = NULL; struct cleanup *old_chain; + struct gdb_exception prev_err; /* Do nothing if we already have an executable filename. */ exec_file = (char *) get_exec_file (0); @@ -182,9 +202,46 @@ exec_file_locate_attach (int pid, int from_tty) old_chain = make_cleanup (xfree, full_exec_path); - exec_file_attach (full_exec_path, from_tty); - symbol_file_add_main (full_exec_path, from_tty); + /* exec_file_attach and symbol_file_add_main may throw an error if the file + cannot be opened either locally or remotely. + + This happens for example, when the file is first found in the local + sysroot (above), and then disappears (a TOCTOU race), or when it doesn't + exist in the target filesystem, or when the file does exist, but + is not readable. + + Even without a symbol file, the remote-based debugging session should + continue normally instead of ending abruptly. Hence we catch thrown + errors/exceptions in the following code. */ + TRY + { + exec_file_attach (full_exec_path, from_tty); + } + CATCH (err, RETURN_MASK_ERROR) + { + if (err.message != NULL) + warning ("%s", err.message); + + prev_err = err; + + /* Save message so it doesn't get trashed by the catch problem"the catch problem below" should be either the "the caught problem below", or "the catch below", I think.
Yeah, i got things mixed up when coming up with it. "the catch below" is what i wanted to say.
+ below. */ + prev_err.message = xstrdup (err.message); + } + END_CATCH + + TRY + { + symbol_file_add_main (full_exec_path, from_tty); + } + CATCH (err, RETURN_MASK_ERROR) + { + if (!exception_print_same (prev_err, err)) + warning ("%s", err.message); + } + END_CATCH + xfree ((void *) prev_err.message);This will reference an uninitialized prev_err.message if the first TRY doesn't throw. Initialize it with: struct gdb_exception prev_err = exception_none;
Done.
Also, it will leak prev_err.message on Ctrl-C/QUIT, which is not caught by RETURN_MASK_ERROR. prev_err.message needs to be freed with a cleanup. Say: struct gdb_exception prev_err = exception_none; old_chain = make_cleanup (xfree, full_exec_path); make_cleanup (free_current_contents, &prev_err.message); TRY { ... } CATCH (err, RETURN_MASK_ERROR) { if (err.message != NULL) warning ("%s", err.message); prev_err = err; prev_err.message = xstrdup (err.message); } ... do_cleanups (old_chain);
Thanks. I've fixed these. I'll get v3 out once the testcase gets reviewed.
Thanks, Pedro Alves
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