[PATCH] perf trace: Fix SIGBUS failures due to misaligned accesses

* [PATCH] perf trace: Fix SIGBUS failures due to misaligned accesses
@ 2015-02-19 20:00 David Ahern
  2015-02-28  9:30 ` [tip:perf/core] " tip-bot for David Ahern
  0 siblings, 1 reply; 2+ messages in thread
From: David Ahern @ 2015-02-19 20:00 UTC (permalink / raw)
  To: acme, linux-kernel; +Cc: David Ahern, Peter Zijlstra, Ingo Molnar

On Sparc64 perf-trace is failing in many spots due to extended load
instructions being used on misaligned accesses.

(gdb) run trace ls
Starting program: /tmp/perf/perf trace ls
[Thread debugging using libthread_db enabled]
Detaching after fork from child process 169460.

<ls output removed>

Program received signal SIGBUS, Bus error.
0x000000000014f4dc in tp_field__u64 (field=0x4cc700, sample=0x7feffffa098) at builtin-trace.c:61
warning: Source file is more recent than executable.
61      TP_UINT_FIELD(64);

(gdb) bt
 0  0x000000000014f4dc in tp_field__u64 (field=0x4cc700, sample=0x7feffffa098) at builtin-trace.c:61
 1  0x0000000000156ad4 in trace__sys_exit (trace=0x7feffffc268, evsel=0x4cc580, event=0xfffffc0104912000,
    sample=0x7feffffa098) at builtin-trace.c:1701
 2  0x0000000000158c14 in trace__run (trace=0x7feffffc268, argc=1, argv=0x7fefffff360) at builtin-trace.c:2160
 3  0x000000000015b78c in cmd_trace (argc=1, argv=0x7fefffff360, prefix=0x0) at builtin-trace.c:2609
 4  0x0000000000107d94 in run_builtin (p=0x4549c8, argc=2, argv=0x7fefffff360) at perf.c:341
 5  0x0000000000108140 in handle_internal_command (argc=2, argv=0x7fefffff360) at perf.c:400
 6  0x0000000000108308 in run_argv (argcp=0x7feffffef2c, argv=0x7feffffef20) at perf.c:444
 7  0x0000000000108728 in main (argc=2, argv=0x7fefffff360) at perf.c:559

(gdb) p *sample
$1 = {ip = 4391276, pid = 169472, tid = 169472, time = 6303014583281250, addr = 0, id = 72082,
  stream_id = 18446744073709551615, period = 1, weight = 0, transaction = 0, cpu = 73, raw_size = 36,
  data_src = 84410401, flags = 0, insn_len = 0, raw_data = 0xfffffc010491203c, callchain = 0x0,
  branch_stack = 0x0, user_regs = {abi = 0, mask = 0, regs = 0x0, cache_regs = 0x7feffffa098, cache_mask = 0},
  intr_regs = {abi = 0, mask = 0, regs = 0x0, cache_regs = 0x7feffffa098, cache_mask = 0}, user_stack = {
    offset = 0, size = 0, data = 0x0}, read = {time_enabled = 0, time_running = 0, {group = {nr = 0,
        values = 0x0}, one = {value = 0, id = 0}}}}
(gdb) p *field
$2 = {offset = 16, {integer = 0x14f4a8 <tp_field__u64>, pointer = 0x14f4a8 <tp_field__u64>}}

sample->raw_data is guaranteed to not be 8-byte aligned because it is preceded
by the size as a u3. So accessing raw data with an extended load instruction causes
the SIGBUS. Resolve by using memcpy to a temporary variable of appropriate size.

Signed-off-by: David Ahern <david.ahern@oracle.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
---
 tools/perf/builtin-trace.c |   36 +++++++++++++++++++++++++++++-------
 1 files changed, 29 insertions(+), 7 deletions(-)

diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
index b1c1df9..d3cab90 100644
--- a/tools/perf/builtin-trace.c
+++ b/tools/perf/builtin-trace.c
@@ -52,7 +52,9 @@ struct tp_field {
 #define TP_UINT_FIELD(bits) \
 static u64 tp_field__u##bits(struct tp_field *field, struct perf_sample *sample) \
 { \
-	return *(u##bits *)(sample->raw_data + field->offset); \
+	u##bits value; \
+	memcpy(&value, sample->raw_data + field->offset, sizeof(value)); \
+	return value;  \
 }
 
 TP_UINT_FIELD(8);
@@ -63,7 +65,8 @@ TP_UINT_FIELD(64);
 #define TP_UINT_FIELD__SWAPPED(bits) \
 static u64 tp_field__swapped_u##bits(struct tp_field *field, struct perf_sample *sample) \
 { \
-	u##bits value = *(u##bits *)(sample->raw_data + field->offset); \
+	u##bits value; \
+	memcpy(&value, sample->raw_data + field->offset, sizeof(value)); \
 	return bswap_##bits(value);\
 }
 
@@ -1513,11 +1516,22 @@ static int trace__read_syscall_info(struct trace *trace, int id)
 	return syscall__set_arg_fmts(sc);
 }
 
+/*
+ * args is to be interpreted as a series of longs but we need to handle
+ * 8-byte unaligned accesses. args points to raw_data within the event
+ * and raw_data is guaranteed to be 8-byte unaligned because it is
+ * preceded by raw_size which is a u32. So we need to copy args to a temp
+ * variable to read it. Most notably this avoids extended load instructions
+ * on unaligned addresses
+ */
+
 static size_t syscall__scnprintf_args(struct syscall *sc, char *bf, size_t size,
-				      unsigned long *args, struct trace *trace,
+				      unsigned char *args, struct trace *trace,
 				      struct thread *thread)
 {
 	size_t printed = 0;
+	unsigned char *p;
+	unsigned long val;
 
 	if (sc->tp_format != NULL) {
 		struct format_field *field;
@@ -1533,12 +1547,17 @@ static size_t syscall__scnprintf_args(struct syscall *sc, char *bf, size_t size,
 		     field = field->next, ++arg.idx, bit <<= 1) {
 			if (arg.mask & bit)
 				continue;
+
+			/* special care for unaligned accesses */
+			p = args + sizeof(unsigned long) * arg.idx;
+			memcpy(&val, p, sizeof(val));
+
 			/*
  			 * Suppress this argument if its value is zero and
  			 * and we don't have a string associated in an
  			 * strarray for it.
  			 */
-			if (args[arg.idx] == 0 &&
+			if (val == 0 &&
 			    !(sc->arg_scnprintf &&
 			      sc->arg_scnprintf[arg.idx] == SCA_STRARRAY &&
 			      sc->arg_parm[arg.idx]))
@@ -1547,23 +1566,26 @@ static size_t syscall__scnprintf_args(struct syscall *sc, char *bf, size_t size,
 			printed += scnprintf(bf + printed, size - printed,
 					     "%s%s: ", printed ? ", " : "", field->name);
 			if (sc->arg_scnprintf && sc->arg_scnprintf[arg.idx]) {
-				arg.val = args[arg.idx];
+				arg.val = val;
 				if (sc->arg_parm)
 					arg.parm = sc->arg_parm[arg.idx];
 				printed += sc->arg_scnprintf[arg.idx](bf + printed,
 								      size - printed, &arg);
 			} else {
 				printed += scnprintf(bf + printed, size - printed,
-						     "%ld", args[arg.idx]);
+						     "%ld", val);
 			}
 		}
 	} else {
 		int i = 0;
 
 		while (i < 6) {
+			/* special care for unaligned accesses */
+			p = args + sizeof(unsigned long) * i;
+			memcpy(&val, p, sizeof(val));
 			printed += scnprintf(bf + printed, size - printed,
 					     "%sarg%d: %ld",
-					     printed ? ", " : "", i, args[i]);
+					     printed ? ", " : "", i, val);
 			++i;
 		}
 	}
-- 
1.7.1


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