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authorSimon Marchi <simon.marchi@efficios.com>2021-01-04 11:56:10 -0500
committerSimon Marchi <simon.marchi@polymtl.ca>2021-01-04 12:00:54 -0500
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tree2409dec31f64c5a58be92ea01787034a44495da0 /gdb/debug.c
parente71daf80d338e536597fa1c3cd1029aadbaa2a67 (diff)
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gdb: introduce scoped debug prints
I spent a lot of time reading infrun debug logs recently, and I think they could be made much more readable by being indented, to clearly see what operation is done as part of what other operation. In the current format, there are no visual cues to tell where things start and end, it's just a big flat list. It's also difficult to understand what caused a given operation (e.g. a call to resume_1) to be done. To help with this, I propose to add the new scoped_debug_start_end structure, along with a bunch of macros to make it convenient to use. The idea of scoped_debug_start_end is simply to print a start and end message at construction and destruction. It also increments/decrements a depth counter in order to make debug statements printed during this range use some indentation. Some care is taken to handle the fact that debug can be turned on or off in the middle of such a range. For example, a "set debug foo 1" command in a breakpoint command, or a superior GDB manually changing the debug_foo variable. Two macros are added in gdbsupport/common-debug.h, which are helpers to define module-specific macros: - scoped_debug_start_end: takes a message that is printed both at construction / destruction, with "start: " and "end: " prefixes. - scoped_debug_enter_exit: prints hard-coded "enter" and "exit" messages, to denote the entry and exit of a function. I added some examples in the infrun module to give an idea of how it can be used and what the result looks like. The macros are in capital letters (INFRUN_SCOPED_DEBUG_START_END and INFRUN_SCOPED_DEBUG_ENTER_EXIT) to mimic the existing SCOPE_EXIT, but that can be changed if you prefer something else. Here's an excerpt of the debug statements printed when doing "continue", where a displaced step is started: [infrun] proceed: enter [infrun] proceed: addr=0xffffffffffffffff, signal=GDB_SIGNAL_DEFAULT [infrun] global_thread_step_over_chain_enqueue: enqueueing thread Thread 0x7ffff75a5640 (LWP 2289301) in global step over chain [infrun] start_step_over: enter [infrun] start_step_over: stealing global queue of threads to step, length = 1 [infrun] start_step_over: resuming [Thread 0x7ffff75a5640 (LWP 2289301)] for step-over [infrun] resume_1: step=1, signal=GDB_SIGNAL_0, trap_expected=1, current thread [Thread 0x7ffff75a5640 (LWP 2289301)] at 0x5555555551bd [displaced] displaced_step_prepare_throw: displaced-stepping Thread 0x7ffff75a5640 (LWP 2289301) now [displaced] prepare: selected buffer at 0x5555555550c2 [displaced] prepare: saved 0x5555555550c2: 1e fa 31 ed 49 89 d1 5e 48 89 e2 48 83 e4 f0 50 [displaced] amd64_displaced_step_copy_insn: copy 0x5555555551bd->0x5555555550c2: c7 45 fc 00 00 00 00 eb 13 8b 05 d4 2e 00 00 83 [displaced] displaced_step_prepare_throw: prepared successfully thread=Thread 0x7ffff75a5640 (LWP 2289301), original_pc=0x5555555551bd, displaced_pc=0x5555555550c2 [displaced] resume_1: run 0x5555555550c2: c7 45 fc 00 [infrun] infrun_async: enable=1 [infrun] prepare_to_wait: prepare_to_wait [infrun] start_step_over: [Thread 0x7ffff75a5640 (LWP 2289301)] was resumed. [infrun] operator(): step-over queue now empty [infrun] start_step_over: exit [infrun] proceed: start: resuming threads, all-stop-on-top-of-non-stop [infrun] proceed: resuming Thread 0x7ffff7da7740 (LWP 2289296) [infrun] resume_1: step=0, signal=GDB_SIGNAL_0, trap_expected=0, current thread [Thread 0x7ffff7da7740 (LWP 2289296)] at 0x7ffff7f7d9b7 [infrun] prepare_to_wait: prepare_to_wait [infrun] proceed: resuming Thread 0x7ffff7da6640 (LWP 2289300) [infrun] resume_1: thread Thread 0x7ffff7da6640 (LWP 2289300) has pending wait status status->kind = stopped, signal = GDB_SIGNAL_TRAP (currently_stepping=0). [infrun] prepare_to_wait: prepare_to_wait [infrun] proceed: [Thread 0x7ffff75a5640 (LWP 2289301)] resumed [infrun] proceed: resuming Thread 0x7ffff6da4640 (LWP 2289302) [infrun] resume_1: thread Thread 0x7ffff6da4640 (LWP 2289302) has pending wait status status->kind = stopped, signal = GDB_SIGNAL_TRAP (currently_stepping=0). [infrun] prepare_to_wait: prepare_to_wait [infrun] proceed: end: resuming threads, all-stop-on-top-of-non-stop [infrun] proceed: exit We can easily see where the call to `proceed` starts and end. We can also see why there are a bunch of resume_1 calls, it's because we are resuming threads, emulating all-stop on top of a non-stop target. We also see that debug statements nest well with other modules that have been migrated to use the "new" debug statement helpers (because they all use debug_prefixed_vprintf in the end. I think this is desirable, for example we could see the debug statements about reading the DWARF info of a library nested under the debug statements about loading that library. Of course, modules that haven't been migrated to use the "new" helpers will still print without indentations. This will be one good reason to migrate them. I think the runtime cost (when debug statements are disabled) of this is reasonable, given the improvement in readability. There is the cost of the conditionals (like standard debug statements), one more condition (if (m_must_decrement_print_depth)) and the cost of constructing a stack object, which means copying a fews pointers. Adding the print in fetch_inferior_event breaks some tests that use "set debug infrun", because it prints a debug statement after the prompt. I adapted these tests to cope with it, by using the "-prompt" switch of gdb_test_multiple to as if this debug statement is part of the expected prompt. It's unfortunate that we have to do this, but I think the debug print is useful, and I don't want a few tests to get in the way of adding good debug output. gdbsupport/ChangeLog: * common-debug.h (debug_print_depth): New. (struct scoped_debug_start_end): New. (scoped_debug_start_end): New. (scoped_debug_enter_exit): New. * common-debug.cc (debug_prefixed_vprintf): Print indentation. gdb/ChangeLog: * debug.c (debug_print_depth): New. * infrun.h (INFRUN_SCOPED_DEBUG_START_END): New. (INFRUN_SCOPED_DEBUG_ENTER_EXIT): New. * infrun.c (start_step_over): Use INFRUN_SCOPED_DEBUG_ENTER_EXIT. (proceed): Use INFRUN_SCOPED_DEBUG_ENTER_EXIT and INFRUN_SCOPED_DEBUG_START_END. (fetch_inferior_event): Use INFRUN_SCOPED_DEBUG_ENTER_EXIT. gdbserver/ChangeLog: * debug.cc (debug_print_depth): New. gdb/testsuite/ChangeLog: * gdb.base/ui-redirect.exp: Expect infrun debug print after prompt. * gdb.threads/ia64-sigill.exp: Likewise. * gdb.threads/watchthreads-reorder.exp: Likewise. Change-Id: I7c3805e6487807aa63a1bae318876a0c69dce949
Diffstat (limited to 'gdb/debug.c')
-rw-r--r--gdb/debug.c4
1 files changed, 4 insertions, 0 deletions
diff --git a/gdb/debug.c b/gdb/debug.c
index 94eb39b..f7dfee1 100644
--- a/gdb/debug.c
+++ b/gdb/debug.c
@@ -23,6 +23,10 @@
/* See gdbsupport/common-debug.h. */
+int debug_print_depth = 0;
+
+/* See gdbsupport/common-debug.h. */
+
void
debug_vprintf (const char *fmt, va_list ap)
{