Re: [RFC/PATCH] perf tools: Introduce perf_thread for backtrace

[Arnaldo Carvalho de Melo]

Em Fri, Nov 20, 2015 at 09:05:23AM +0000, åæéå / HIRAMATUïMASAMI escreveu:
> >From: Namhyung Kim [mailto:namhyung@xxxxxxxxxx]
> >
> >Backtrace is a crucial info for debugging.  And upcoming refcnt
> >tracking facility also wants to use it.
> >
> >So instead of relying on glibc's backtrace_symbols[_fd] which misses
> >some (static) functions , use our own symbol searching mechanism.  To
> >do that, add perf_thread global variable to keep its maps and symbols.
> 
> Hmm, I doubt that this can work for debugging situation, because
> sometimes backtrace facilities has to debug itself by itself.

That is a valid point, possibly we can have both and when we think that
the code we rely on for resolving symbols has issues, activate the
other, more expensive, binutils/elfutils spawned command line utilities
to do compare the results?
 
> For the some (static) functions, I'd rather like to use glibc's 
> backtrace_symbols and addr2line or even with raw address for
> reliability...

 
> Thank you,
> 
> >
> >The backtrace output from TUI is changed like below.  (I made a key
> >action to generate a segfault for testing):
> >
> >Before:
> >  perf: Segmentation fault
> >  -------- backtrace --------
> >  perf[0x544a8b]
> >  /usr/lib/libc.so.6(+0x33680)[0x7fc46420b680]
> >  perf[0x54041b]
> >  perf(perf_evlist__tui_browse_hists+0x91)[0x5432e1]
> >  perf(cmd_report+0x1d20)[0x43cb10]
> >  perf[0x487073]
> >  perf(main+0x62f)[0x42cb1f]
> >  /usr/lib/libc.so.6(__libc_start_main+0xf0)[0x7fc4641f8610]
> >  perf(_start+0x29)[0x42cc39]
> >  [0x0]
> >
> >After:
> >  perf: Segmentation fault
> >  -------- backtrace --------
> >  perf_evsel__hists_browse(+0x43b) in perf [0x54066b]
> >  perf_evlist__tui_browse_hists(+0x91) in perf [0x543531]
> >  cmd_report(+0x1d20) in perf [0x43cb50]
> >  run_builtin(+0x53) in perf [0x4870b3]
> >  main(+0x634) in perf [0x42cb54]
> >  __libc_start_main(+0xf0) in libc-2.22.so [0x7fea3577c610]
> >  _start(+0x29) in perf [0x42cc79]
> >  [0x0]
> >
> >Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
> >Cc: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx>
> >Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxxx>
> >---
> > tools/perf/perf.c         |  7 +++++-
> > tools/perf/ui/tui/setup.c | 21 ++++++++++++++--
> > tools/perf/util/util.c    | 62 +++++++++++++++++++++++++++++++++++++++++++++++
> > tools/perf/util/util.h    |  5 ++++
> > 4 files changed, 92 insertions(+), 3 deletions(-)
> >
> >diff --git a/tools/perf/perf.c b/tools/perf/perf.c
> >index 4bee53c3f796..f77eb440b05c 100644
> >--- a/tools/perf/perf.c
> >+++ b/tools/perf/perf.c
> >@@ -604,6 +604,8 @@ int main(int argc, const char **argv)
> > 	 */
> > 	pthread__block_sigwinch();
> >
> >+	create_perf_thread();
> >+
> > 	while (1) {
> > 		static int done_help;
> > 		int was_alias = run_argv(&argc, &argv);
> >@@ -615,7 +617,7 @@ int main(int argc, const char **argv)
> > 			fprintf(stderr, "Expansion of alias '%s' failed; "
> > 				"'%s' is not a perf-command\n",
> > 				cmd, argv[0]);
> >-			goto out;
> >+			goto out_destroy;
> > 		}
> > 		if (!done_help) {
> > 			cmd = argv[0] = help_unknown_cmd(cmd);
> >@@ -626,6 +628,9 @@ int main(int argc, const char **argv)
> >
> > 	fprintf(stderr, "Failed to run command '%s': %s\n",
> > 		cmd, strerror_r(errno, sbuf, sizeof(sbuf)));
> >+
> >+out_destroy:
> >+	destroy_perf_thread();
> > out:
> > 	return 1;
> > }
> >diff --git a/tools/perf/ui/tui/setup.c b/tools/perf/ui/tui/setup.c
> >index 7dfeba0a91f3..bc2da884e65a 100644
> >--- a/tools/perf/ui/tui/setup.c
> >+++ b/tools/perf/ui/tui/setup.c
> >@@ -13,6 +13,8 @@
> > #include "../libslang.h"
> > #include "../keysyms.h"
> > #include "tui.h"
> >+#include "../../util/symbol.h"
> >+#include "../../util/thread.h"
> >
> > static volatile int ui__need_resize;
> >
> >@@ -96,14 +98,29 @@ int ui__getch(int delay_secs)
> > static void ui__signal_backtrace(int sig)
> > {
> > 	void *stackdump[32];
> >-	size_t size;
> >+	size_t size, i;
> >
> > 	ui__exit(false);
> > 	psignal(sig, "perf");
> >
> > 	printf("-------- backtrace --------\n");
> > 	size = backtrace(stackdump, ARRAY_SIZE(stackdump));
> >-	backtrace_symbols_fd(stackdump, size, STDOUT_FILENO);
> >+	/* skip first two stack frame (for this function and signal stack) */
> >+	for (i = 2; i < size; i++) {
> >+		struct addr_location al = {
> >+			.sym = NULL,
> >+		};
> >+
> >+		thread__find_addr_location(perf_thread, PERF_RECORD_MISC_USER,
> >+					   MAP__FUNCTION, (long)stackdump[i], &al);
> >+
> >+		if (al.sym)
> >+			printf("%s(+0x%"PRIx64") in ", al.sym->name,
> >+			       map__map_ip(al.map, (u64)stackdump[i]) - al.sym->start);
> >+		if (al.map)
> >+			printf("%s ", al.map->dso->short_name);
> >+		printf("[0x%lx]\n", (unsigned long)stackdump[i]);
> >+	}
> >
> > 	exit(0);
> > }
> >diff --git a/tools/perf/util/util.c b/tools/perf/util/util.c
> >index 75759aebc7b8..f1a26ea14053 100644
> >--- a/tools/perf/util/util.c
> >+++ b/tools/perf/util/util.c
> >@@ -16,6 +16,9 @@
> > #include <linux/kernel.h>
> > #include <unistd.h>
> > #include "callchain.h"
> >+#include "machine.h"
> >+#include "thread.h"
> >+#include "thread_map.h"
> >
> > struct callchain_param	callchain_param = {
> > 	.mode	= CHAIN_GRAPH_ABS,
> >@@ -696,3 +699,62 @@ fetch_kernel_version(unsigned int *puint, char *str,
> > 		*puint = (version << 16) + (patchlevel << 8) + sublevel;
> > 	return 0;
> > }
> >+
> >+
> >+static int process_event(struct perf_tool *tool, union perf_event *event,
> >+			 struct perf_sample *sample, struct machine *machine)
> >+{
> >+	switch (event->header.type) {
> >+	case PERF_RECORD_COMM:
> >+		return tool->comm(tool, event, sample, machine);
> >+	case PERF_RECORD_MMAP:
> >+		return tool->mmap(tool, event, sample, machine);
> >+	case PERF_RECORD_MMAP2:
> >+		return tool->mmap2(tool, event, sample, machine);
> >+	default:
> >+		break;
> >+	}
> >+	return 0;
> >+}
> >+
> >+struct thread *perf_thread;
> >+
> >+void create_perf_thread(void)
> >+{
> >+	struct perf_tool tool = {
> >+		.comm	= perf_event__process_comm,
> >+		.mmap	= perf_event__process_mmap,
> >+		.mmap2	= perf_event__process_mmap2,
> >+	};
> >+	struct thread_map *tm;
> >+	struct machine *machine;
> >+	int pid = getpid();
> >+
> >+	machine = machine__new_host();
> >+	if (machine == NULL)
> >+		return;
> >+
> >+	tm = thread_map__new_dummy();
> >+	if (tm == NULL) {
> >+		machine__delete(machine);
> >+		return;
> >+	}
> >+
> >+	thread_map__set_pid(tm, 0, pid);
> >+
> >+	perf_event__synthesize_thread_map(&tool, tm, process_event, machine,
> >+					  false, 500);
> >+
> >+	perf_thread = machine__find_thread(machine, pid, pid);
> >+	BUG_ON(perf_thread == NULL);
> >+
> >+	thread_map__put(tm);
> >+}
> >+
> >+void destroy_perf_thread(void)
> >+{
> >+	struct machine *machine = perf_thread->mg->machine;
> >+
> >+	machine__delete_threads(machine);
> >+	machine__delete(machine);
> >+}
> >diff --git a/tools/perf/util/util.h b/tools/perf/util/util.h
> >index dcc659017976..630e145049aa 100644
> >--- a/tools/perf/util/util.h
> >+++ b/tools/perf/util/util.h
> >@@ -358,4 +358,9 @@ int fetch_kernel_version(unsigned int *puint,
> > #define KVER_FMT	"%d.%d.%d"
> > #define KVER_PARAM(x)	KVER_VERSION(x), KVER_PATCHLEVEL(x), KVER_SUBLEVEL(x)
> >
> >+extern struct thread *perf_thread;
> >+
> >+void create_perf_thread(void);
> >+void destroy_perf_thread(void);
> >+
> > #endif /* GIT_COMPAT_UTIL_H */
> >--
> >2.6.2
> 
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