Hi,
I see this testcase occasionally failing. After reproducing it with
verbose output and checking objdump output I found at least 3 scenarios
where data read from objdump output does not match:
1. same byte is repeated in objdump output
Note that byte at ffffffff815cf071 is in output twice
ffffffff815cf06e <sysret_check+0x4b>:
ffffffff815cf06e: 24 2f and $0x2f,%al
ffffffff815cf070: 00 0f add %cl,(%rdi)
ffffffff815cf071 <sysret_careful>:
ffffffff815cf071: 0f ba e2 03 bt $0x3,%edx
ffffffff815cf075: 73 11 jae
2. objdump output can span across multiple sections
For example in case of libcrc32c.ko and start_address=8 .text
sections ends at 6b, but test continues to read output from
.init.text:
Disassembly of section .text:
0000000000000008 <crc32c+0x8>:
8: 48 89 e5 mov %rsp,%rbp
b: 53 push %rbx
c: 8b 01 mov (%rcx),%eax
...
6b: 90 nop
Disassembly of section .init.text:
0000000000000008 <init_module+0x8>:
8: 00 00 add %al,(%rax)
a: 00 00 add %al,(%rax)
c: 48 89 e5 mov %rsp,%rbp
3. gaps in output
For example, note that byte at ffffffff81670500 is missing:
ffffffff816704fe <sysret_check+0x4b>:
ffffffff816704fe: 7b 34 jnp ffffffff81670534
<sysret_signal+0x1c>
...
ffffffff81670501 <sysret_careful>:
ffffffff81670501: 0f ba e2 03 bt $0x3,%edx
ffffffff81670505: 73 11 jae ffffffff81670518
<sysret_signal>
My idea to fix this (attached) was to change objdump output reading
from sequential to offset-based - to take into account offset of
each line. And if offset starts going backwards, stop reading.
Comments/other ideas are welcome.
Regards,
Jan
diff --git a/tools/perf/tests/code-reading.c b/tools/perf/tests/code-reading.c
index f671ec3..4c3d87c 100644
--- a/tools/perf/tests/code-reading.c
+++ b/tools/perf/tests/code-reading.c
@@ -33,20 +33,20 @@ static unsigned int hex(char c)
return c - 'A' + 10;
}
-static void read_objdump_line(const char *line, size_t line_len, void **buf,
- size_t *len)
+static size_t read_objdump_line(const char *line, size_t line_len, void *buf,
+ size_t len)
{
const char *p;
- size_t i;
+ size_t i, j = 0;
/* Skip to a colon */
p = strchr(line, ':');
if (!p)
- return;
+ return 0;
i = p + 1 - line;
/* Read bytes */
- while (*len) {
+ while (j < len) {
char c1, c2;
/* Skip spaces */
@@ -65,20 +65,24 @@ static void read_objdump_line(const char *line, size_t line_len, void **buf,
if (i < line_len && line[i] && !isspace(line[i]))
break;
/* Store byte */
- *(unsigned char *)*buf = (hex(c1) << 4) | hex(c2);
- *buf += 1;
- *len -= 1;
+ *(unsigned char *)buf = (hex(c1) << 4) | hex(c2);
+ buf += 1;
+ j++;
}
+ /* return number of succesfully read bytes */
+ return j;
}
-static int read_objdump_output(FILE *f, void **buf, size_t *len)
+static int read_objdump_output(FILE *f, void *buf, size_t *len, u64 start_addr)
{
char *line = NULL;
- size_t line_len;
+ size_t line_len, off, off_last = 0, read_bytes, written_bytes;
ssize_t ret;
int err = 0;
+ u64 addr, last_addr = start_addr;
+ unsigned char tmp[BUFSZ];
- while (1) {
+ while (off_last < *len) {
ret = getline(&line, &line_len, f);
if (feof(f))
break;
@@ -87,9 +91,33 @@ static int read_objdump_output(FILE *f, void **buf, size_t *len)
err = -1;
break;
}
- read_objdump_line(line, ret, buf, len);
+
+ /* read objdump data into temporary buffer */
+ read_bytes = read_objdump_line(line, ret, tmp, sizeof(tmp));
+ if (!read_bytes)
+ continue;
+
+ if (sscanf(line, "%"PRIx64, &addr) != 1)
+ continue;
+ if (addr < last_addr) {
+ pr_debug("addr going backwards, read beyond section?\n");
+ break;
+ }
+ last_addr = addr;
+
+ /* copy it from temporary buffer to 'buf' according
+ * to address on current objdump line */
+ off = addr - start_addr;
+ if (off >= *len)
+ break;
+ written_bytes = MIN(read_bytes, *len - off);
+ memcpy(buf + off, tmp, written_bytes);
+ off_last = off + written_bytes;
}
+ /* len returns number of bytes that could not be read */
+ *len -= off_last;
+
free(line);
return err;
@@ -103,7 +131,8 @@ static int read_via_objdump(const char *filename, u64 addr, void *buf,
FILE *f;
int ret;
- fmt = "%s -d --start-address=0x%"PRIx64" --stop-address=0x%"PRIx64" %s";
+ /* -z parameter helps to avoid gaps in objdump output */
+ fmt = "%s -z -d --start-address=0x%"PRIx64" --stop-address=0x%"PRIx64" %s";
ret = snprintf(cmd, sizeof(cmd), fmt, "objdump", addr, addr + len,
filename);
if (ret <= 0 || (size_t)ret >= sizeof(cmd))
@@ -120,7 +149,7 @@ static int read_via_objdump(const char *filename, u64 addr, void *buf,
return -1;
}
- ret = read_objdump_output(f, &buf, &len);
+ ret = read_objdump_output(f, buf, &len, addr);
if (len) {
pr_debug("objdump read too few bytes\n");
if (!ret)
@@ -132,6 +161,18 @@ static int read_via_objdump(const char *filename, u64 addr, void *buf,
return ret;
}
+static void dump_buf(unsigned char *buf, size_t len)
+{
+ size_t i;
+
+ for (i = 0; i < len; i++) {
+ pr_debug("0x%02x ", buf[i]);
+ if (i % 16 == 15)
+ pr_debug("\n");
+ }
+ pr_debug("\n");
+}
+
static int read_object_code(u64 addr, size_t len, u8 cpumode,
struct thread *thread, struct state *state)
{
@@ -234,6 +275,10 @@ static int read_object_code(u64 addr, size_t len, u8 cpumode,
/* The results should be identical */
if (memcmp(buf1, buf2, len)) {
pr_debug("Bytes read differ from those read by objdump\n");
+ pr_debug("buf1:\n");
+ dump_buf(buf1, len);
+ pr_debug("buf2:\n");
+ dump_buf(buf2, len);
return -1;
}
pr_debug("Bytes read match those read by objdump\n");
