perf tools: Make perf able to read files from older ABIs

This patches provides a way to handle legacy perf.data
files.  Legacy files are those using the older PERFFILE
signature.

For those, it is still necessary to detect endianness but
without comparing their header->attr_size with the
tool's own version as it may be different. Instead, we use
a reference table for all known sizes from the legacy era.

We try all the combinations for sizes and endianness. If we find
a match, we proceed, otherwise we return: "incompatible file
format".

This is also done for the pipe-mode file format.

Signed-off-by: Stephane Eranian <eranian@google.com>
Cc: peterz@infradead.org
Cc: acme@redhat.com
Cc: robert.richter@amd.com
Cc: ming.m.lin@intel.com
Cc: andi@firstfloor.org
Cc: asharma@fb.com
Cc: ravitillo@lbl.gov
Cc: vweaver1@eecs.utk.edu
Cc: khandual@linux.vnet.ibm.com
Cc: dsahern@gmail.com
Link: http://lkml.kernel.org/r/1328826068-11713-19-git-send-email-eranian@google.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 94 insertions, 28 deletions

diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
index 6d580267d043..c851495b9b48 100644
--- a/tools/perf/util/header.c
+++ b/tools/perf/util/header.c
@@ -1803,35 +1803,101 @@ out_free:
         return err;
 }
 
-static int check_magic_endian(u64 *magic, struct perf_file_header *header,
-                              struct perf_header *ph)
+static const int attr_file_abi_sizes[] = {
+        [0] = PERF_ATTR_SIZE_VER0,
+        [1] = PERF_ATTR_SIZE_VER1,
+        0,
+};
+
+/*
+ * In the legacy file format, the magic number is not used to encode endianness.
+ * hdr_sz was used to encode endianness. But given that hdr_sz can vary based
+ * on ABI revisions, we need to try all combinations for all endianness to
+ * detect the endianness.
+ */
+static int try_all_file_abis(uint64_t hdr_sz, struct perf_header *ph)
 {
-        int ret;
+        uint64_t ref_size, attr_size;
+        int i;
 
-        /* check for legacy format */
-        ret = memcmp(magic, __perf_magic1, sizeof(*magic));
-        if (ret == 0) {
-                pr_debug("legacy perf.data format\n");
-                if (!header)
-                        return -1;
+        for (i = 0 ; attr_file_abi_sizes[i]; i++) {
+                ref_size = attr_file_abi_sizes[i]
+                         + sizeof(struct perf_file_section);
+                if (hdr_sz != ref_size) {
+                        attr_size = bswap_64(hdr_sz);
+                        if (attr_size != ref_size)
+                                continue;
 
-                if (header->attr_size != sizeof(struct perf_file_attr)) {
-                        u64 attr_size = bswap_64(header->attr_size);
+                        ph->needs_swap = true;
+                }
+                pr_debug("ABI%d perf.data file detected, need_swap=%d\n",
+                         i,
+                         ph->needs_swap);
+                return 0;
+        }
+        /* could not determine endianness */
+        return -1;
+}
 
-                        if (attr_size != sizeof(struct perf_file_attr))
-                                return -1;
+#define PERF_PIPE_HDR_VER0      16
+
+static const size_t attr_pipe_abi_sizes[] = {
+        [0] = PERF_PIPE_HDR_VER0,
+        0,
+};
+
+/*
+ * In the legacy pipe format, there is an implicit assumption that endiannesss
+ * between host recording the samples, and host parsing the samples is the
+ * same. This is not always the case given that the pipe output may always be
+ * redirected into a file and analyzed on a different machine with possibly a
+ * different endianness and perf_event ABI revsions in the perf tool itself.
+ */
+static int try_all_pipe_abis(uint64_t hdr_sz, struct perf_header *ph)
+{
+        u64 attr_size;
+        int i;
+
+        for (i = 0 ; attr_pipe_abi_sizes[i]; i++) {
+                if (hdr_sz != attr_pipe_abi_sizes[i]) {
+                        attr_size = bswap_64(hdr_sz);
+                        if (attr_size != hdr_sz)
+                                continue;
 
                         ph->needs_swap = true;
                 }
+                pr_debug("Pipe ABI%d perf.data file detected\n", i);
                 return 0;
         }
+        return -1;
+}
+
+static int check_magic_endian(u64 magic, uint64_t hdr_sz,
+                              bool is_pipe, struct perf_header *ph)
+{
+        int ret;
+
+        /* check for legacy format */
+        ret = memcmp(&magic, __perf_magic1, sizeof(magic));
+        if (ret == 0) {
+                pr_debug("legacy perf.data format\n");
+                if (is_pipe)
+                        return try_all_pipe_abis(hdr_sz, ph);
+
+                return try_all_file_abis(hdr_sz, ph);
+        }
+        /*
+         * the new magic number serves two purposes:
+         * - unique number to identify actual perf.data files
+         * - encode endianness of file
+         */
 
-        /* check magic number with same endianness */
-        if (*magic == __perf_magic2)
+        /* check magic number with one endianness */
+        if (magic == __perf_magic2)
                 return 0;
 
-        /* check magic number but opposite endianness */
-        if (*magic != __perf_magic2_sw)
+        /* check magic number with opposite endianness */
+        if (magic != __perf_magic2_sw)
                 return -1;
 
         ph->needs_swap = true;
@@ -1850,8 +1916,11 @@ int perf_file_header__read(struct perf_file_header *header,
         if (ret <= 0)
                 return -1;
 
-        if (check_magic_endian(&header->magic, header, ph) < 0)
+        if (check_magic_endian(header->magic,
+                               header->attr_size, false, ph) < 0) {
+                pr_debug("magic/endian check failed\n");
                 return -1;
+        }
 
         if (ph->needs_swap) {
                 mem_bswap_64(header, offsetof(struct perf_file_header,
@@ -1938,21 +2007,17 @@ static int perf_file_header__read_pipe(struct perf_pipe_file_header *header,
         if (ret <= 0)
                 return -1;
 
-         if (check_magic_endian(&header->magic, NULL, ph) < 0)
+        if (check_magic_endian(header->magic, header->size, true, ph) < 0) {
+                pr_debug("endian/magic failed\n");
                 return -1;
+        }
+
+        if (ph->needs_swap)
+                header->size = bswap_64(header->size);
 
         if (repipe && do_write(STDOUT_FILENO, header, sizeof(*header)) < 0)
                 return -1;
 
-        if (header->size != sizeof(*header)) {
-                u64 size = bswap_64(header->size);
-
-                if (size != sizeof(*header))
-                        return -1;
-
-                ph->needs_swap = true;
-        }
-
         return 0;
 }
 
@@ -1992,6 +2057,7 @@ static int read_attr(int fd, struct perf_header *ph,
 
         /* on file perf_event_attr size */
         sz = attr->size;
+
         if (ph->needs_swap)
                 sz = bswap_32(sz);