[Libunwind-devel] Remote unwinding support for perf on MIPS

[Sapir Natan]

Hi,

 

We are trying to obtain a callgraph using ‘perf’ utility, while running on MIPS architecture with linux 3.10 (64Bit processes)

We wish to obtain callgraph on:

·         Terminated processes

·         Running processes (using –p <pid>)

 

Following the resolution that perf is unable to create callgraph on MIPS using frame pointer, we tried using libunwind

Since ‘dwarf’ option for perf isn’t part of linux 3.10 (or any other version), we added a patch (composed of the following 3 patches):

·         https://www.linux-mips.org/archives/linux-mips/2013-05/msg00123.html

·         https://www.linux-mips.org/archives/linux-mips/2013-05/msg00115.html

·         https://www.linux-mips.org/archives/linux-mips/2016-04/msg00003.html

·         As part of the patch we also linked ‘perf’ with ‘libunwind’ (open source version 1.2.1).

 

This patch added the ‘dwarf’ capability to ‘perf’ on MIPS, however we still couldn’t obtain a usable callgraph (most functions had no trace)

The problem we encountered was that when reaching ‘maps__find´ function (linux/tools/perf/util/map.c), the binary search for the required entry failed (could not be located)

From our investigation, we can support local unwinding but not remote (which is the type of unwinding required by ‘perf’)

 

Checking online we saw on ‘libunwind’ NEWS: ‘** Mips remote unwind support’ for version 1.3.

We replaced our ‘1.2.1’ version with ‘1.3-rc1’ and re-checked, however the results remained the same (no callgraph).

 

Could you please assist?

·         What was the issue you encountered that the fix in 1.3 version resolved?

·         Can the new addition enable ‘perf’ to support callgraph on MIPS?

·         Did we miss anything in our steps (as described above)?

·         Can you advice on the next steps?

 

Thanks,

Sapir