Re: [PATCH v4 18/18] perf: make perf able to read file from older ABIs

[Anshuman Khandual <khandual@linux.vnet.ibm.com>]

On Saturday 28 January 2012 02:26 AM, Stephane Eranian wrote:
> 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>
> ---
>  tools/perf/util/header.c |  126 +++++++++++++++++++++++++++++++++++----------
>  1 files changed, 98 insertions(+), 28 deletions(-)
> 
> diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
> index 1fb365d..a15f451 100644
> --- a/tools/perf/util/header.c
> +++ b/tools/perf/util/header.c
> @@ -1630,35 +1630,102 @@ int perf_header__process_sections(struct perf_header *header, int fd,
>  	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)
> +{
> +	uint64_t ref_size;
> +	int i;
> +
> +	for (i = 0 ; attr_pipe_abi_sizes[i]; i++) {
> +		if (hdr_sz != attr_pipe_abi_sizes[i]) {
> +			u64 attr_size = bswap_64(hdr_sz);
> +
> +			if (attr_size != ref_size)

'ref_size' never got a value here but being checked against. This statement hits a compilation
failure. 

cc1: warnings being treated as errors
util/header.c: In function ‘try_all_pipe_abis’:
util/header.c:1692: error: ‘ref_size’ may be used uninitialized in this function
make: *** [util/header.o] Error 1

> +				continue;
> 
>  			ph->needs_swap = true;
>  		}
> +		pr_debug("Pipe ABI%d perf.data file detected\n", i);
>  		return 0;
>  	}
> +	return -1;
> +}
> 
> -	/* check magic number with same endianness */
> -	if (*magic == __perf_magic2)
> +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 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;
> @@ -1677,8 +1744,11 @@ 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,
> @@ -1924,21 +1994,17 @@ 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;
>  }
> 
> @@ -1975,6 +2041,10 @@ static int read_attr(int fd, struct perf_header *ph,
> 
>  	/* on file perf_event_attr size */
>  	sz = attr->size;
> +	if (sz != our_sz)
> +		pr_debug("on file attr=%zu vs. %zu bytes,"
> +			 " ignoring extra fields\n", sz, our_sz);
> +
>  	if (ph->needs_swap)
>  		sz = bswap_32(sz);
> 


-- 
Anshuman Khandual
Linux Technology Centre
IBM Systems and Technology Group