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

[Sapir Natan]

Hi Luke,

 

Thank you very much for your reply.
I am afraid I haven’t seen ‘_UPT_access_mem.c’ or ‘_UPT_reg_offset.c’ linked to perf or called from it at all (or anything from libunwind-ptrace).

It is also already part of version 1.3-rc1, which means my perf still fails to unwind even with this latest fix.

 

Did this patch fix the perf unwinding on MIPS issue for you?

If so, can you tell me which patch you used to add this capability to perf on MIPS? (patch to the linux code)

Is there anything I’m missing here?

 

Thanks,

Sapir

 

From: Luke Diamand [mailto:address@hidden
Sent: Sunday, July 29, 2018 8:59 PM
To: Sergey Korolev
Cc: Sapir Natan; Chen Muchtar; Roi Chen; address@hidden
Subject: Re: [Libunwind-devel] Remote unwinding support for perf on MIPS

 

I had a similar problem on mipsel32. At least on that the problem was that the accessor function was calling read_s32 which seems to do the wrong thing on that platform. Fixing that seems to have made it work. I'm in the process of trying to organise a patch.

 

On Sun, 29 Jul 2018, 18:25 Sergey Korolev, <address@hidden> wrote:

In my opinion a mentioned patch [1] does not work properly

since it defines _UPT_reg_offset elements as

+    [UNW_MIPS_R0]  =  0,
+    [UNW_MIPS_R1]  =  1,
+    [UNW_MIPS_R2]  =  2,
+    [UNW_MIPS_R3]  =  3,
+    [UNW_MIPS_R4]  =  4,
+    [UNW_MIPS_R5]  =  5,
+    [UNW_MIPS_R6]  =  6,
+    [UNW_MIPS_R7]  =  7,
+    [UNW_MIPS_R8]  =  8,
+    [UNW_MIPS_R9]  =  9,
+    [UNW_MIPS_R10] = 10,
+    [UNW_MIPS_R11] = 11,
+    [UNW_MIPS_R12] = 12,
+    [UNW_MIPS_R13] = 13,
+    [UNW_MIPS_R14] = 14,
+    [UNW_MIPS_R15] = 15,
+    [UNW_MIPS_R16] = 16,
+    [UNW_MIPS_R17] = 17,
+    [UNW_MIPS_R18] = 18,
+    [UNW_MIPS_R19] = 19,
+    [UNW_MIPS_R20] = 20,
+    [UNW_MIPS_R21] = 21,
+    [UNW_MIPS_R22] = 22,
+    [UNW_MIPS_R23] = 23,
+    [UNW_MIPS_R24] = 24,
+    [UNW_MIPS_R25] = 25,
+    [UNW_MIPS_R26] = 26,
+    [UNW_MIPS_R27] = 27,
+    [UNW_MIPS_R28] = 28,
+    [UNW_MIPS_R29] = 29,
+    [UNW_MIPS_R30] = 30,
+    [UNW_MIPS_R31] = 31,
+    [UNW_MIPS_PC]  = 64,

 

but a code in _UPT_access_mem.c expects that _UPT_reg_offset

is a byte offset, and not a word offset or a register index.

 

[1] http://git.savannah.gnu.org/gitweb/?p=libunwind.git;a=commit;h=2a5d1a629634b3225fccb1ed8a0a765bccc77f2e

 

On Sun, Jul 29, 2018 at 6:18 PM, Sapir Natan <address@hidden> wrote:

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

 

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