[PATCH] perf tools: fix endian conversion reading event attr from header

[PATCH] perf tools: fix endian conversion reading event attr from header

[David Ahern]

The perf_event_attr struct has 2 __u32's at the top and need to
be swapped individually. With this change I was able to analyze
a perf.data collected in a 32-bit PPC VM on an x86 system. I
tested both 32-bit and 64-bit binaries for the Intel analysis
side; both read the PPC perf.data file correctly.

Signed-off-by: David Ahern <dsahern@gmail.com>
---
 tools/perf/util/header.c |    9 ++++++++-
 1 files changed, 8 insertions(+), 1 deletions(-)

diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
index afb0849..8044c6f 100644
--- a/tools/perf/util/header.c
+++ b/tools/perf/util/header.c
@@ -877,9 +877,16 @@ int perf_session__read_header(struct perf_session *session, int fd)
 		struct perf_evsel *evsel;
 		off_t tmp;
 
-		if (perf_header__getbuffer64(header, fd, &f_attr, sizeof(f_attr)))
+		if (readn(fd, &f_attr, sizeof(f_attr)) <= 0)
 			goto out_errno;
 
+		if (header->needs_swap) {
+			f_attr.attr.type = bswap_32(f_attr.attr.type);
+			f_attr.attr.size = bswap_32(f_attr.attr.size);
+			mem_bswap_64(&f_attr.attr.config,
+				     sizeof(struct perf_event_attr) - 8);
+		}
+
 		tmp = lseek(fd, 0, SEEK_CUR);
 		evsel = perf_evsel__new(&f_attr.attr, i);
 
-- 
1.7.6

Re: [PATCH] perf tools: fix endian conversion reading event attr from header

[David Ahern]

On 07/12/2011 09:19 AM, David Ahern wrote:
> The perf_event_attr struct has 2 __u32's at the top and need to
> be swapped individually. With this change I was able to analyze
> a perf.data collected in a 32-bit PPC VM on an x86 system. I
> tested both 32-bit and 64-bit binaries for the Intel analysis
> side; both read the PPC perf.data file correctly.

Similarly with this one. It replaces a call to perf_header__getbuffer64
with what it does inline -- only doing the swap of the attr struct after
the initial 2 u32's. I spent 2 days tracking this down and would hate to
lose it waiting for Arnaldo's return.

David

> 
> Signed-off-by: David Ahern <dsahern@gmail.com>
> ---
>  tools/perf/util/header.c |    9 ++++++++-
>  1 files changed, 8 insertions(+), 1 deletions(-)
> 
> diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
> index afb0849..8044c6f 100644
> --- a/tools/perf/util/header.c
> +++ b/tools/perf/util/header.c
> @@ -877,9 +877,16 @@ int perf_session__read_header(struct perf_session *session, int fd)
>  		struct perf_evsel *evsel;
>  		off_t tmp;
>  
> -		if (perf_header__getbuffer64(header, fd, &f_attr, sizeof(f_attr)))
> +		if (readn(fd, &f_attr, sizeof(f_attr)) <= 0)
>  			goto out_errno;
>  
> +		if (header->needs_swap) {
> +			f_attr.attr.type = bswap_32(f_attr.attr.type);
> +			f_attr.attr.size = bswap_32(f_attr.attr.size);
> +			mem_bswap_64(&f_attr.attr.config,
> +				     sizeof(struct perf_event_attr) - 8);
> +		}
> +
>  		tmp = lseek(fd, 0, SEEK_CUR);
>  		evsel = perf_evsel__new(&f_attr.attr, i);
>  

Re: [PATCH] perf tools: fix endian conversion reading event attr from header

[Frederic Weisbecker]

On Tue, Jul 12, 2011 at 09:19:19AM -0600, David Ahern wrote:
> The perf_event_attr struct has 2 __u32's at the top and need to
> be swapped individually. With this change I was able to analyze
> a perf.data collected in a 32-bit PPC VM on an x86 system. I
> tested both 32-bit and 64-bit binaries for the Intel analysis
> side; both read the PPC perf.data file correctly.
> 
> Signed-off-by: David Ahern <dsahern@gmail.com>
> ---
>  tools/perf/util/header.c |    9 ++++++++-
>  1 files changed, 8 insertions(+), 1 deletions(-)
> 
> diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
> index afb0849..8044c6f 100644
> --- a/tools/perf/util/header.c
> +++ b/tools/perf/util/header.c
> @@ -877,9 +877,16 @@ int perf_session__read_header(struct perf_session *session, int fd)
>  		struct perf_evsel *evsel;
>  		off_t tmp;
>  
> -		if (perf_header__getbuffer64(header, fd, &f_attr, sizeof(f_attr)))
> +		if (readn(fd, &f_attr, sizeof(f_attr)) <= 0)
>  			goto out_errno;
>  
> +		if (header->needs_swap) {
> +			f_attr.attr.type = bswap_32(f_attr.attr.type);
> +			f_attr.attr.size = bswap_32(f_attr.attr.size);
> +			mem_bswap_64(&f_attr.attr.config,
> +				     sizeof(struct perf_event_attr) - 8);
> +		}
> +

Good catch!

But would be nice to also handle the wakeup_events and bp_type fields.

Thanks.

>  		tmp = lseek(fd, 0, SEEK_CUR);
>  		evsel = perf_evsel__new(&f_attr.attr, i);
>  
> -- 
> 1.7.6
> 

Re: [PATCH] perf tools: fix endian conversion reading event attr from header

[David Ahern]

On 07/15/2011 09:47 AM, Frederic Weisbecker wrote:
>> -		if (perf_header__getbuffer64(header, fd, &f_attr, sizeof(f_attr)))
>> +		if (readn(fd, &f_attr, sizeof(f_attr)) <= 0)
>>  			goto out_errno;
>>  
>> +		if (header->needs_swap) {
>> +			f_attr.attr.type = bswap_32(f_attr.attr.type);
>> +			f_attr.attr.size = bswap_32(f_attr.attr.size);
>> +			mem_bswap_64(&f_attr.attr.config,
>> +				     sizeof(struct perf_event_attr) - 8);
>> +		}
>> +
> 
> Good catch!

A long, painful discovery

> But would be nice to also handle the wakeup_events and bp_type fields.
> 

I did not think those values were used in userspace, so did not touch
them. But then your inquiry pushed me into cscope and I found the
perf_event__attr_swap() function. I'll redo the patch leveraging the
swapping done there.

David