From 57d1de9cf3ba8dd98eaf4a3d131c05ec4c49779d Mon Sep 17 00:00:00 2001 From: Luis Machado Date: Wed, 13 Apr 2016 15:17:22 -0500 Subject: [PATCH] Debugging without a binary (regression) 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 warning: /tmp/symbol-file: Permission denied. 0xf7ddb2d0 in ?? () (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) This is caused by a couple of function calls within exec_file_locate_attach that can potentially throw errors. The following patch guards both exec_file_attach and symbol_file_add_main to prevent the errors from disrupting the connection process. There was also a case where native GDB tripped on this problem, but it was mostly fixed by bf74e428bca61022bd5cdf6bf28789a184748b4d. Regression-tested on x86-64/Ubuntu. gdb/ChangeLog: 2016-04-13 Luis Machado * exec.c (exec_file_locate_attach): Guard a couple functions that can throw errors. (exception_print_same): New helper function. --- gdb/ChangeLog | 6 ++++++ gdb/exec.c | 60 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++-- 2 files changed, 64 insertions(+), 2 deletions(-) diff --git a/gdb/ChangeLog b/gdb/ChangeLog index d03d5ae..ad74df6 100644 --- a/gdb/ChangeLog +++ b/gdb/ChangeLog @@ -1,3 +1,9 @@ +2016-04-13 Luis Machado + + * exec.c (exec_file_locate_attach): Guard a couple functions + that can throw errors. + (exception_print_same): New helper function. + 2016-04-13 Pedro Alves PR remote/19840 diff --git a/gdb/exec.c b/gdb/exec.c index a10ab9b..c998ab1 100644 --- a/gdb/exec.c +++ b/gdb/exec.c @@ -135,6 +135,25 @@ exec_file_clear (int from_tty) printf_unfiltered (_("No executable file now.\n")); } +/* Returns non-zero if exceptions E1 and E2 are equal. Returns zero + otherwise. */ + +static int +exception_print_same (struct gdb_exception e1, struct gdb_exception e2) +{ + const char *msg1 = e1.message; + const char *msg2 = e2.message; + + if (msg1 == NULL) + msg1 = ""; + if (msg2 == NULL) + msg2 = ""; + + return (e1.reason == e2.reason + && e1.error == e2.error + && strcmp (e1.message, e2.message) == 0); +} + /* See gdbcore.h. */ 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 = exception_none; /* Do nothing if we already have an executable filename. */ exec_file = (char *) get_exec_file (0); @@ -181,9 +201,45 @@ exec_file_locate_attach (int pid, int from_tty) } old_chain = make_cleanup (xfree, full_exec_path); + make_cleanup (free_current_contents, &prev_err.message); + + /* 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 below. */ + prev_err.message = xstrdup (err.message); + } + END_CATCH - exec_file_attach (full_exec_path, from_tty); - symbol_file_add_main (full_exec_path, from_tty); + 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 do_cleanups (old_chain); } -- 2.7.4