runtime/pprof: package emits invalid memory profile

[gopherbot]

by majek04:

What steps will reproduce the problem?

    $ cat << EOF > simple.mprof
heap profile: 10141899: 3497395080 [61368113: 46518687552] @ heap/1048576
6: 0 [12: 192] @ 0x42d56f 0x42e8c8 0x417e07 0x417fdd 0x601887 0x602f11 0x5140dc 0x51431c
0x51431c 0x514596 0x514ef5 0x510ccf 0x50b523 0x4c32ed 0x4ca90d 0x425b20
53: 0 [159: 2544] @ 0x42d56f 0x42e9d1 0x42ea5a 0x42a4ad 0x42a3e8 0x4e27cf 0x4e26bb
0x511722 0x512d4f 0x514d4d 0x5138bf 0x512b75 0x514d4d 0x510ccf 0x50b523 0x4c32ed
0x4ca90d 0x425b20
    EOF
    $ go tool pprof /bin/sh simple.mprof 

(simple.mprof also available here  [1])

What is the expected output?

    Although I simplified the mprof file, the two extracted lines are from real profile. Either the memory profiler is broken to generate this lines or the pprof is broken not to accept it. Or most likely both.

    The problem is with the second field. Pprof assumes that if first field is not zero, second must not be zero. This is not the case in mprofs generated in real world.

What do you see instead?

    pprof crashes. It should not.

Which version are you using?  (run 'go version')

    $ hg id
    87dea3f5ebe7+ (release-branch.go1.2) go1.2/release


Please provide any additional information below.

    Here's a quick-and-dirty patch [2]. Not sure if it's correct as I can't find any documentation of mprof file format.

[1] 
https://gist.github.com/majek/fe71148abac09b7f867a/raw/34f4d1978b816e02557d2d3b26038da123ef34c9/simple.mprof

[2]
https://gist.github.com/majek/fe71148abac09b7f867a/raw/28fc6638e8e699ac0e87300eed3bfb4254384c2f/pprof.patch

[DanielMorsing]

Comment 1:

The profile is saying that a non-zero number of objects are occupying zero bytes. I'm
pretty sure this is a bug in the runtime since we don't profile zero sized allocations.

Labels changed: added repo-main, release-go1.3maybe.

Status changed to Accepted.

[dvyukov]

Comment 2:

How to reproduce this bad profile?
Can you please symbolize it or create an svg from it?

[DanielMorsing]

Comment 3:

The pprof tool just fails to start and I can't make an svg or symbolize the profile
without removing the offending entry.

[dvyukov]

Comment 4:

But it must work with the fix [2]. Or plain addr2line must work.

[DanielMorsing]

Comment 5:

Did some text surgery on the memprof file. The offending entry is created at
src/pkg/crypto/x509/pkix/pkix.go:80

[dvyukov]

Comment 6:

what version of Go? OS? is it possible to reproduce it?

[DanielMorsing]

Comment 7:

Using Go 1.2, running on Linux. It happens about once a week, but I've yet to find a
reproducer.
I'll insert some checks into our runtime so that I have more info once this happens next.

[dvyukov]

Comment 8:

I've tried to run std tests with the following patch and -memprofilerate=1024:
https://golang.org/cl/62130043/diff/20001/src/pkg/runtime/mprof.goc
but it did not catch anything.
Maybe it will help you to localize the problem...

[rsc]

Comment 9:

Labels changed: added release-none, removed release-go1.3maybe.