perf intel-pt: Support itrace option flag d+e to log on error

Pass d+e option and log size via intel_pt_log_enable(). Allocate a buffer
for log messages and provide intel_pt_log_dump_buf() to dump and reset the
buffer upon decoder errors.

Example:

$ sudo perf record -e intel_pt// sleep 1
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.094 MB perf.data ]
$ sudo perf config itrace.debug-log-buffer-size=300
$ sudo perf script --itrace=ed+e+o | head -20
Dumping debug log buffer (first line may be sliced)
Other
ffffffff96ca22f6: 48 89 e5 Other
ffffffff96ca22f9: 65 48 8b 05 ff e0 38 69 Other
ffffffff96ca2301: 48 3d c0 a5 c1 98 Other
ffffffff96ca2307: 74 08 Jcc +8
ffffffff96ca2311: 5d Other
ffffffff96ca2312: c3 Ret
ERROR: Bad RET compression (TNT=N) at 0xffffffff96ca2312
End of debug log buffer dump
instruction trace error type 1 time 15913.537143482 cpu 5 pid 36292 tid 36292 ip 0xffffffff96ca2312 code 6: Trace doesn't match instruction
Dumping debug log buffer (first line may be sliced)
Other
ffffffff96ce7fe9: f6 47 2e 20 Other
ffffffff96ce7fed: 74 11 Jcc +17
ffffffff96ce7fef: 48 8b 87 28 0a 00 00 Other
ffffffff96ce7ff6: 5d Other
ffffffff96ce7ff7: 48 8b 40 18 Other
ffffffff96ce7ffb: c3 Ret
ERROR: Bad RET compression (TNT=N) at 0xffffffff96ce7ffb
Warning:
8 instruction trace errors

Reviewed-by: Andi Kleen <[e-mail]>
Reviewed-by: Namhyung Kim <[e-mail]>
Signed-off-by: Adrian Hunter <[e-mail]>
Cc: Ian Rogers <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/Documentation/perf-intel-pt.txt

···
 
 		-a	Suppress logging of perf events
 		+a	Log all perf events
+		+e	Output only on decoding errors (size configurable)
 		+o	Output to stdout instead of "intel_pt.log"
 
 By default, logged perf events are filtered by any specified time ranges, but
-flag +a overrides that.
+flag +a overrides that.  The +e flag can be useful for analyzing errors.  By
+default, the log size in that case is 16384 bytes, but can be altered by
+linkperf:perf-config[1] e.g. perf config itrace.debug-log-buffer-size=30000
 
 In addition, the period of the "instructions" event can be specified. e.g.
 

tools/perf/util/intel-pt-decoder/intel-pt-log.c

···
  */
 
 #include <stdio.h>
+#include <stdlib.h>
 #include <stdint.h>
 #include <inttypes.h>
 #include <stdarg.h>
 #include <stdbool.h>
 #include <string.h>
+
+#include <linux/zalloc.h>
+#include <linux/kernel.h>
 
 #include "intel-pt-log.h"
 #include "intel-pt-insn-decoder.h"
···
 
 #define MAX_LOG_NAME 256
 
+#define DFLT_BUF_SZ	(16 * 1024)
+
+struct log_buf {
+	char			*buf;
+	size_t			buf_sz;
+	size_t			head;
+	bool			wrapped;
+	FILE			*backend;
+};
+
 static FILE *f;
 static char log_name[MAX_LOG_NAME];
 bool intel_pt_enable_logging;
+static bool intel_pt_dump_log_on_error;
+static unsigned int intel_pt_log_on_error_size;
+static struct log_buf log_buf;
 
 void *intel_pt_log_fp(void)
 {
 	return f;
 }
 
-void intel_pt_log_enable(void)
+void intel_pt_log_enable(bool dump_log_on_error, unsigned int log_on_error_size)
 {
 	intel_pt_enable_logging = true;
+	intel_pt_dump_log_on_error = dump_log_on_error;
+	intel_pt_log_on_error_size = log_on_error_size;
 }
 
 void intel_pt_log_disable(void)
···
 	fprintf(f, " ");
 }
 
+static ssize_t log_buf__write(void *cookie, const char *buf, size_t size)
+{
+	struct log_buf *b = cookie;
+	size_t sz = size;
+
+	if (!b->buf)
+		return size;
+
+	while (sz) {
+		size_t space = b->buf_sz - b->head;
+		size_t n = min(space, sz);
+
+		memcpy(b->buf + b->head, buf, n);
+		sz -= n;
+		buf += n;
+		b->head += n;
+		if (sz && b->head >= b->buf_sz) {
+			b->head = 0;
+			b->wrapped = true;
+		}
+	}
+	return size;
+}
+
+static int log_buf__close(void *cookie)
+{
+	struct log_buf *b = cookie;
+
+	zfree(&b->buf);
+	return 0;
+}
+
+static FILE *log_buf__open(struct log_buf *b, FILE *backend, unsigned int sz)
+{
+	cookie_io_functions_t fns = {
+		.write = log_buf__write,
+		.close = log_buf__close,
+	};
+	FILE *file;
+
+	memset(b, 0, sizeof(*b));
+	b->buf_sz = sz;
+	b->buf = malloc(b->buf_sz);
+	b->backend = backend;
+	file = fopencookie(b, "a", fns);
+	if (!file)
+		zfree(&b->buf);
+	return file;
+}
+
+static void log_buf__dump(struct log_buf *b)
+{
+	if (!b->buf)
+		return;
+
+	fflush(f);
+	fprintf(b->backend, "Dumping debug log buffer (first line may be sliced)\n");
+	if (b->wrapped)
+		fwrite(b->buf + b->head, b->buf_sz - b->head, 1, b->backend);
+	fwrite(b->buf, b->head, 1, b->backend);
+	fprintf(b->backend, "End of debug log buffer dump\n");
+
+	b->head = 0;
+	b->wrapped = false;
+}
+
+void intel_pt_log_dump_buf(void)
+{
+	log_buf__dump(&log_buf);
+}
+
 static int intel_pt_log_open(void)
 {
 	if (!intel_pt_enable_logging)
···
 		f = fopen(log_name, "w+");
 	else
 		f = stdout;
+	if (f && intel_pt_dump_log_on_error)
+		f = log_buf__open(&log_buf, f, intel_pt_log_on_error_size);
 	if (!f) {
 		intel_pt_enable_logging = false;
 		return -1;

tools/perf/util/intel-pt-decoder/intel-pt-log.h

···
 struct intel_pt_pkt;
 
 void *intel_pt_log_fp(void);
-void intel_pt_log_enable(void);
+void intel_pt_log_enable(bool dump_log_on_error, unsigned int log_on_error_size);
 void intel_pt_log_disable(void);
 void intel_pt_log_set_name(const char *name);
+void intel_pt_log_dump_buf(void);
 
 void __intel_pt_log_packet(const struct intel_pt_pkt *packet, int pkt_len,
 			   uint64_t pos, const unsigned char *buf);

tools/perf/util/intel-pt.c

···
 				pid_t pid, pid_t tid, u64 ip, u64 timestamp,
 				pid_t machine_pid, int vcpu)
 {
+	bool dump_log_on_error = pt->synth_opts.log_plus_flags & AUXTRACE_LOG_FLG_ON_ERROR;
+	bool log_on_stdout = pt->synth_opts.log_plus_flags & AUXTRACE_LOG_FLG_USE_STDOUT;
 	union perf_event event;
 	char msg[MAX_AUXTRACE_ERROR_MSG];
 	int err;
···
 	auxtrace_synth_guest_error(&event.auxtrace_error, PERF_AUXTRACE_ERROR_ITRACE,
 				   code, cpu, pid, tid, ip, msg, timestamp,
 				   machine_pid, vcpu);
+
+	if (intel_pt_enable_logging && !log_on_stdout) {
+		FILE *fp = intel_pt_log_fp();
+
+		if (fp)
+			perf_event__fprintf_auxtrace_error(&event, fp);
+	}
+
+	if (code != INTEL_PT_ERR_LOST && dump_log_on_error)
+		intel_pt_log_dump_buf();
 
 	err = perf_session__deliver_synth_event(pt->session, &event, NULL);
 	if (err)
···
 		goto err_delete_thread;
 	}
 
-	if (pt->synth_opts.log)
-		intel_pt_log_enable();
+	if (pt->synth_opts.log) {
+		bool log_on_error = pt->synth_opts.log_plus_flags & AUXTRACE_LOG_FLG_ON_ERROR;
+		unsigned int log_on_error_size = pt->synth_opts.log_on_error_size;
+
+		intel_pt_log_enable(log_on_error, log_on_error_size);
+	}
 
 	/* Maximum non-turbo ratio is TSC freq / 100 MHz */
 	if (pt->tc.time_mult) {