[Libunwind-devel] User stack unwind issue on mips64r6el platform

Hi,

I am trying to capture user stack callgraph on MIPS64R6EL platform(Boston), but unfortunately I failed to get the user stack unwind info.

My environment info is:

kernel version: 5.0-rc1

libunwind: 1.3.1

test platform: Qemu for boston

I applied the patch from David Daney and made some modification for linux kernel 5.0.

I use 'perf record --call-graph dwarf ./test' to record, but only get following info:

38.95% 38.95% 2-mips-2 2-mips-2 [.] .L12

---test_hi (inlined!!)

38.95% 0.00% 2-mips-2 2-mips-2 [.] test_hi (inlined)

---test_hi (inlined!!)

30.05% 30.05% 2-mips-2 2-mips-2 [.] .L9

---test_high (inlined!!)

30.05% 0.00% 2-mips-2 2-mips-2 [.] test_high (inlined)

---test_high (inlined!!)

The same test program running under x86 can get full call graph from main to test_high etc:

- 41.12% 41.10% 2 2 [.] test_hi

41.09% _start

__libc_start_main

main

test_hi

- 32.44% 32.39% 2 2 [.] test_high

32.39% _start

__libc_start_main

main

test_high

According to the discuss between Luke and Sapir(https://lists.libreplanet.org/archive/html/libunwind-devel/2018-07/msg00005.html), I double checked .eh_frame section has already been generated.

Two things are weird:

1. in _Umips_dwarf_search_unwind_table, IP register value is out of the range betwee pi->start_ip and pi->end_ip, this directs unw_step return error and could find the stack levels.

2. The test_high function are cross assembled into following three sections and in the perf sample, the user IP register always pointer to section .L9 not section test_high. I am not sure if this directs the unwind info can't be decoded correctly.

0000000000000da0 <test_high>:

da0: 67bdffd0 daddiu sp,sp,-48

da4: ffbf0028 sd ra,40(sp)

da8: ffbe0020 sd s8,32(sp)

dac: ffbc0018 sd gp,24(sp)

db0: 03a0f025 move s8,sp

db4: 3c1c0002 lui gp,0x2

db8: 0399e02d daddu gp,gp,t9

dbc: 679c8670 daddiu gp,gp,-31120

dc0: df828060 ld v0,-32672(gp)

dc4: 0040c825 move t9,v0

dc8: f8190000 jalrc t9

dcc: afc00000 sw zero,0(s8)

dd0: c8000005 bc de8 <.L8>

0000000000000dd4 <.L9>:

dd4: 8fc20000 lw v0,0(s8)

dd8: afc20004 sw v0,4(s8)

ddc: 8fc20000 lw v0,0(s8)

de0: 24420001 addiu v0,v0,1

de4: afc20000 sw v0,0(s8)

0000000000000de8 <.L8>:

de8: 8fc20000 lw v0,0(s8)

dec: 3c03055d lui v1,0x55d

df0: 34634a7f ori v1,v1,0x4a7f

df4: 5862fff7 bgec v1,v0,dd4 <.L9>

df8: 00000000 nop

dfc: 03c0e825 move sp,s8

e00: dfbf0028 ld ra,40(sp)

e04: dfbe0020 ld s8,32(sp)

e08: dfbc0018 ld gp,24(sp)

e0c: 67bd0030 daddiu sp,sp,48

e10: d81f0000 jrc ra

Could you please help with this? Any suggestion is welcomed:).

From:	Yan Archer
Subject:	[Libunwind-devel] User stack unwind issue on mips64r6el platform
Date:	Mon, 4 Mar 2019 16:05:04 +0000