[Libunwind-devel] Unwinding on arm and division by zero

Hello All,

I’m currently using the library in order to trace remote applications once an exception is detected.

It works pretty well for almost all the exceptions, but I encounter some unexpected behavior on division by 0 (as an example).

Using a sample application I get the following backtrace using the library:

====== backtrace:

261: exchnd_test

/lib/libpthread-2.18.so(raise+0x24)[0x76eea93c]

/bin/exchnd_test(__aeabi_ldiv0+0xc)[0xb108]

From this point unw_step returns 0.

Meanwhile, if I use GDB on the same application:

(gdb) bt

#0 0x76fbe93c in raise () from /lib/libpthread.so.0

#1 0x0000b108 in __aeabi_ldiv0 () at /arm-none-linux-gnueabi/src/gcc/libgcc/config/arm/lib1funcs.S:1331

#2 0x00008dc8 in function_div0last () at src/exchnd_test.c:281

#3 function_div03 () at src/exchnd_test.c:287

#4 function_div02 () at src/exchnd_test.c:292

#5 function_div01 (myvalue=0) at src/exchnd_test.c:298

#6 main (argc=<optimized out>, argv=<optimized out>) at src/exchnd_test.c:988

#7 0x76e652bc in __libc_start_main () from /lib/libc.so.6

#8 0x00009404 in _start () at ../ports/sysdeps/arm/start.S:124

As you can guess from these callstack, I’m working on ARM.

From what I can tel from the objdump, gcc has optimized the call in this example, but that doesn’t explain why we don’t see __libc_start_main (as we see it in other exception cases).

On all SIGFPE exception I saw until now, unw_step always stopped on __aeabi_ldiv0.

Any idea on what can happened there ?

Best regards

Frederic Berat

See below for some more information. I’m sorry in advance if a lot of things below are useless.

Application build command:

arm-none-linux-gnueabi-gcc -Wall -Wextra -Wformat -Wno-format-nonliteral -Wformat-security -Wformat-y2k -Werror -g -O3 -rdynamic -mtp=auto -mfloat-abi=softfp -mfpu=vfpv3-d16 -march=armv7-a -mtune=cortex-a9 -DG_BYTE_ORDER=G_LITTLE_ENDIAN -ffunction-sections -fdata-sections -funwind- -o exchnd_test.o -c src/exchnd_test.c

libunwind configuration:

configure --build=x86_64-linux --host=arm-mel-linux-gnueabi --target=arm-mel-linux-gnueabi --prefix=/usr --exec_prefix=/usr --bindir=/usr/bin --sbindir=/usr/sbin --libexecdir=/usr/lib/libunwind --datadir=/usr/share --sysconfdir=/etc --sharedstatedir=/com --localstatedir=/var --libdir=/usr/lib --includedir=/usr/include --oldincludedir=/usr/include --infodir=/usr/share/info --mandir=/usr/share/man --disable-silent-rules --disable-dependency-tracking --enable-minidebuginfo

Libunwund version: 1.1

I also tried with libunwind head and the following configuration and different UNW_ARM_UNWIND_METHOD env values:

The result is the same.

Concerning the test application:

====== processor registers:

R0: 00000000 R1: 00000117 R2: 00000008 R3: 76f5f4c0 R4: 7e88bc58 R5: 00000000

R6: 000093d8 R7: 0000010c R8: 00000000 R9: 00000000 R10: 76f64000

FP: 00000000 IP: 76f23918 SP: 7e88acfc LR: 0000b108 PC: 76f2393c CPSR: 20000010

====== stack dump:

<7e88acfc> 00000000 00000000 00008dc8 00000000 ................

<7e88ad0c> 00000000 00000000 00000000 00000000 ................

--- Skip zeroed

<7e88b27c> 00000000 00000000 00000000 001356cc .............V..

<7e88b28c> 76eea000 7e88b2d8 76ee9e24 ffffffff ...v...~$..v....

<7e88b29c> 00000000 00000000 00000000 00000000 ................

--- Skip zeroed

<7e88b2bc> 00000000 00000000 0012d000 0012ce28 ............(...

<7e88b2cc> 0012ce28 00000000 00000005 00135000 (............P..

<7e88b2dc> 00138000 00137e24 0013a5a8 0012d000 ....$~..........

<7e88b2ec> 00000003 00000000 00000000 00000000 ................

<7e88b2fc> 00000000 00000000 00000000 00000000 ................

<7e88b30c> 00015000 00014b10 00014b10 7e88b60c .P...K...K.....~

<7e88b31c> 7e88b66c 7e88b4f4 7e88b52c 76f573f8 l..~...~,..~.s.v

<7e88b32c> 00000020 7e88b60c 7e88b37c 00000000 ......~|..~....

<7e88b33c> 00000000 00000000 00000000 00000000 ................

<7e88b34c> 00000000 7e88b388 00000003 00000000 .......~........

<7e88b35c> 76f61ba0 76f61ba0 76f471f0 76f64960 ...v...v.q.v`I.v

<7e88b36c> 007a33b8 00000000 00000000 00000000 .3z.............

<7e88b37c> 76f64058 00000003 76f61ba0 76eea000 address@hidden

<7e88b38c> 76f4310c 00000000 00000000 0000362e .1.v.........6..

<7e88b39c> 00362e6f 00362e6f 00362e6f 00000000 o.6.o.6.o.6.....

<7e88b3ac> 00000000 00000003 76f61658 0012d000 ........X..v....

<7e88b3bc> 00138e23 76eec5a8 76f3cdf0 00000000 #......v...v....

<7e88b3cc> 76dc3e8e 00000000 76f44774 7e88b390 .>.v....tG.v...~

<7e88b3dc> 00000003 00000000 76f16457 00000000 ........Wd.v....

<7e88b3ec> 76f44774 00000003 7e88b4f4 76ef8df7 tG.v.......~...v

<7e88b3fc> 73516240 00000001 6474e552 7e88b2c0 @bQs....R.td...~

<7e88b40c> 0013a5a8 76ef8df7 00000000 00000000 .......v........

<7e88b41c> 007a33b8 000081a4 00000001 00000000 .3z.............

<7e88b42c> 00000000 00000000 00000000 00000000 ................

<7e88b43c> 00000000 00131668 00000000 00001000 ....h...........

<7e88b44c> 00000000 00000990 00000000 5506b429 ............)..U

<7e88b45c> 34ef21f2 550063b9 00000000 5506b411 .!.4.c.U.......U

Sections:

Idx Name Size VMA LMA File off Algn

0 .interp 00000013 00008134 00008134 00000134 2**0

CONTENTS, ALLOC, LOAD, READONLY, DATA

1 .note.ABI-tag 00000020 00008148 00008148 00000148 2**2

CONTENTS, ALLOC, LOAD, READONLY, DATA

2 .hash 00000148 00008168 00008168 00000168 2**2

CONTENTS, ALLOC, LOAD, READONLY, DATA

3 .dynsym 000002b0 000082b0 000082b0 000002b0 2**2

CONTENTS, ALLOC, LOAD, READONLY, DATA

4 .dynstr 000001e3 00008560 00008560 00000560 2**0

CONTENTS, ALLOC, LOAD, READONLY, DATA

5 .gnu.version 00000056 00008744 00008744 00000744 2**1

CONTENTS, ALLOC, LOAD, READONLY, DATA

6 .gnu.version_r 00000060 0000879c 0000879c 0000079c 2**2

CONTENTS, ALLOC, LOAD, READONLY, DATA

7 .rel.dyn 00000020 000087fc 000087fc 000007fc 2**2

CONTENTS, ALLOC, LOAD, READONLY, DATA

8 .rel.plt 00000110 0000881c 0000881c 0000081c 2**2

CONTENTS, ALLOC, LOAD, READONLY, DATA

9 .init 0000000c 0000892c 0000892c 0000092c 2**2

CONTENTS, ALLOC, LOAD, READONLY, CODE

10 .plt 000001ac 00008938 00008938 00000938 2**2

CONTENTS, ALLOC, LOAD, READONLY, CODE

11 .text 00002690 00008ae4 00008ae4 00000ae4 2**2

CONTENTS, ALLOC, LOAD, READONLY, CODE

12 .fini 00000008 0000b174 0000b174 00003174 2**2

CONTENTS, ALLOC, LOAD, READONLY, CODE

13 .rodata 00001db4 0000b17c 0000b17c 0000317c 2**2

CONTENTS, ALLOC, LOAD, READONLY, DATA

14 .ARM.extab 00000060 0000cf30 0000cf30 00004f30 2**2

CONTENTS, ALLOC, LOAD, READONLY, DATA

15 .ARM.exidx 000000f0 0000cf90 0000cf90 00004f90 2**2

CONTENTS, ALLOC, LOAD, READONLY, DATA

16 .eh_frame 00000004 0000d080 0000d080 00005080 2**2

CONTENTS, ALLOC, LOAD, READONLY, DATA

17 .init_array 00000004 00015084 00015084 00005084 2**2

CONTENTS, ALLOC, LOAD, DATA

18 .fini_array 00000004 00015088 00015088 00005088 2**2

CONTENTS, ALLOC, LOAD, DATA

19 .jcr 00000004 0001508c 0001508c 0000508c 2**2

CONTENTS, ALLOC, LOAD, DATA

20 .dynamic 000000f8 00015090 00015090 00005090 2**2

CONTENTS, ALLOC, LOAD, DATA

21 .got 00000098 00015188 00015188 00005188 2**2

CONTENTS, ALLOC, LOAD, DATA

22 .data 000003c0 00015220 00015220 00005220 2**2

CONTENTS, ALLOC, LOAD, DATA

23 .bss 0002d778 000155e0 000155e0 000055e0 2**3

ALLOC

24 .comment 00000041 00000000 00000000 000055e0 2**0

CONTENTS, READONLY

25 .ARM.attributes 00000033 00000000 00000000 00005621 2**0

CONTENTS, READONLY

26 .debug_aranges 00000228 00000000 00000000 00005658 2**3

CONTENTS, READONLY, DEBUGGING

27 .debug_info 00004533 00000000 00000000 00005880 2**0

CONTENTS, READONLY, DEBUGGING

28 .debug_abbrev 00000bdc 00000000 00000000 00009db3 2**0

CONTENTS, READONLY, DEBUGGING

29 .debug_line 00001047 00000000 00000000 0000a98f 2**0

CONTENTS, READONLY, DEBUGGING

30 .debug_frame 000003fc 00000000 00000000 0000b9d8 2**2

CONTENTS, READONLY, DEBUGGING

31 .debug_str 000018ee 00000000 00000000 0000bdd4 2**0

CONTENTS, READONLY, DEBUGGING

32 .debug_loc 000014bb 00000000 00000000 0000d6c2 2**0

CONTENTS, READONLY, DEBUGGING

33 .debug_ranges 00000488 00000000 00000000 0000eb80 2**3

CONTENTS, READONLY, DEBUGGING

Contents of section .ARM.extab:

cf30 08b10181 b0b00084 00000000 08b10181 ................

cf40 b0b00084 00000000 08b10181 b0b00084 ................

cf50 00000000 08b10181 b0b003a9 00000000 ................

cf60 deb20181 b003a905 00000000 08b10181 ................

cf70 b0b003a9 00000000 82b20181 b0b0a907 ................

cf80 00000000 c6b20181 b0b0af06 00000000 ................

Contents of section .ARM.exidx:

cf90 54bbff7f f0ffff7f 40c4ff7f 01000000 address@hidden

cfa0 98c4ff7f 8cffff7f c8c4ff7f 90ffff7f ................

cfb0 00c5ff7f b0b0a880 20c5ff7f 8cffff7f ........ .......

cfc0 4cc5ff7f b0aa0780 d4c5ff7f b0ab0880 L...............

cfd0 9cc6ff7f b0b0a880 d4c6ff7f b003a880 ................

cfe0 30c7ff7f 70ffff7f 1cc8ff7f b003a880 0...p...........

cff0 80c8ff7f 03af0280 f8c9ff7f 64ffff7f ............d...

d000 84caff7f b003a880 d4caff7f 60ffff7f ............`...

d010 28cbff7f 64ffff7f 94cbff7f b0b0a880 (...d...........

d020 10ccff7f ab08b180 64ccff7f b0b0b080 ........d.......

d030 d4ccff7f ab08b180 24cfff7f b0b0ac80 ........$.......

d040 64d0ff7f ab08b180 0cd3ff7f b0b0a880 d...............

d050 64d3ff7f b0ad1c80 70d4ff7f b0af0a80 d.......p.......

d060 5cdeff7f 01000000 a4e0ff7f ad08b180 \...............

d070 00e1ff7f b0b0b080 fce0ff7f 01000000 ................

0000b0fc <__aeabi_idiv0>:

b0fc: e92d4002 push {r1, lr}

b100: e3a00008 mov r0, #8

b104: ebfff613 bl 8958 <_init+0x2c>

b108: e8bd8002 pop {r1, pc}

0000aebc <__aeabi_idiv>:

aebc: e3510000 cmp r1, #0

aec0: 0a000081 beq b0cc <.divsi3_skip_div0_test+0x208>

0000aec4 <.divsi3_skip_div0_test>:

aec4: e020c001 eor ip, r0, r1

aec8: 42611000 rsbmi r1, r1, #0

aecc: e2512001 subs r2, r1, #1

aed0: 0a000070 beq b098 <.divsi3_skip_div0_test+0x1d4>

aed4: e1b03000 movs r3, r0

aed8: 42603000 rsbmi r3, r0, #0

aedc: e1530001 cmp r3, r1

aee0: 9a00006f bls b0a4 <.divsi3_skip_div0_test+0x1e0>

aee4: e1110002 tst r1, r2

aee8: 0a000071 beq b0b4 <.divsi3_skip_div0_test+0x1f0>

aeec: e16f2f13 clz r2, r3

aef0: e16f0f11 clz r0, r1

aef4: e0402002 sub r2, r0, r2

aef8: e272201f rsbs r2, r2, #31

aefc: 10822082 addne r2, r2, r2, lsl #1

af00: e3a00000 mov r0, #0

af04: 108ff102 addne pc, pc, r2, lsl #2

af08: e1a00000 nop ; (mov r0, r0)

af0c: e1530f81 cmp r3, r1, lsl #31

af10: e0a00000 adc r0, r0, r0

af14: 20433f81 subcs r3, r3, r1, lsl #31

af18: e1530f01 cmp r3, r1, lsl #30

af1c: e0a00000 adc r0, r0, r0

af20: 20433f01 subcs r3, r3, r1, lsl #30

af24: e1530e81 cmp r3, r1, lsl #29

af28: e0a00000 adc r0, r0, r0

af2c: 20433e81 subcs r3, r3, r1, lsl #29

af30: e1530e01 cmp r3, r1, lsl #28

af34: e0a00000 adc r0, r0, r0

af38: 20433e01 subcs r3, r3, r1, lsl #28

af3c: e1530d81 cmp r3, r1, lsl #27

af40: e0a00000 adc r0, r0, r0

af44: 20433d81 subcs r3, r3, r1, lsl #27

af48: e1530d01 cmp r3, r1, lsl #26

af4c: e0a00000 adc r0, r0, r0

af50: 20433d01 subcs r3, r3, r1, lsl #26

af54: e1530c81 cmp r3, r1, lsl #25

af58: e0a00000 adc r0, r0, r0

af5c: 20433c81 subcs r3, r3, r1, lsl #25

af60: e1530c01 cmp r3, r1, lsl #24

af64: e0a00000 adc r0, r0, r0

af68: 20433c01 subcs r3, r3, r1, lsl #24

af6c: e1530b81 cmp r3, r1, lsl #23

af70: e0a00000 adc r0, r0, r0

af74: 20433b81 subcs r3, r3, r1, lsl #23

af78: e1530b01 cmp r3, r1, lsl #22

af7c: e0a00000 adc r0, r0, r0

af80: 20433b01 subcs r3, r3, r1, lsl #22

af84: e1530a81 cmp r3, r1, lsl #21

af88: e0a00000 adc r0, r0, r0

af8c: 20433a81 subcs r3, r3, r1, lsl #21

af90: e1530a01 cmp r3, r1, lsl #20

af94: e0a00000 adc r0, r0, r0

af98: 20433a01 subcs r3, r3, r1, lsl #20

af9c: e1530981 cmp r3, r1, lsl #19

afa0: e0a00000 adc r0, r0, r0

afa4: 20433981 subcs r3, r3, r1, lsl #19

afa8: e1530901 cmp r3, r1, lsl #18

afac: e0a00000 adc r0, r0, r0

afb0: 20433901 subcs r3, r3, r1, lsl #18

afb4: e1530881 cmp r3, r1, lsl #17

afb8: e0a00000 adc r0, r0, r0

afbc: 20433881 subcs r3, r3, r1, lsl #17

afc0: e1530801 cmp r3, r1, lsl #16

afc4: e0a00000 adc r0, r0, r0

afc8: 20433801 subcs r3, r3, r1, lsl #16

afcc: e1530781 cmp r3, r1, lsl #15

afd0: e0a00000 adc r0, r0, r0

afd4: 20433781 subcs r3, r3, r1, lsl #15

afd8: e1530701 cmp r3, r1, lsl #14

afdc: e0a00000 adc r0, r0, r0

afe0: 20433701 subcs r3, r3, r1, lsl #14

afe4: e1530681 cmp r3, r1, lsl #13

afe8: e0a00000 adc r0, r0, r0

afec: 20433681 subcs r3, r3, r1, lsl #13

aff0: e1530601 cmp r3, r1, lsl #12

aff4: e0a00000 adc r0, r0, r0

aff8: 20433601 subcs r3, r3, r1, lsl #12

affc: e1530581 cmp r3, r1, lsl #11

b000: e0a00000 adc r0, r0, r0

b004: 20433581 subcs r3, r3, r1, lsl #11

b008: e1530501 cmp r3, r1, lsl #10

b00c: e0a00000 adc r0, r0, r0

b010: 20433501 subcs r3, r3, r1, lsl #10

b014: e1530481 cmp r3, r1, lsl #9

b018: e0a00000 adc r0, r0, r0

b01c: 20433481 subcs r3, r3, r1, lsl #9

b020: e1530401 cmp r3, r1, lsl #8

b024: e0a00000 adc r0, r0, r0

b028: 20433401 subcs r3, r3, r1, lsl #8

b02c: e1530381 cmp r3, r1, lsl #7

b030: e0a00000 adc r0, r0, r0

b034: 20433381 subcs r3, r3, r1, lsl #7

b038: e1530301 cmp r3, r1, lsl #6

b03c: e0a00000 adc r0, r0, r0

b040: 20433301 subcs r3, r3, r1, lsl #6

b044: e1530281 cmp r3, r1, lsl #5

b048: e0a00000 adc r0, r0, r0

b04c: 20433281 subcs r3, r3, r1, lsl #5

b050: e1530201 cmp r3, r1, lsl #4

b054: e0a00000 adc r0, r0, r0

b058: 20433201 subcs r3, r3, r1, lsl #4

b05c: e1530181 cmp r3, r1, lsl #3

b060: e0a00000 adc r0, r0, r0

b064: 20433181 subcs r3, r3, r1, lsl #3

b068: e1530101 cmp r3, r1, lsl #2

b06c: e0a00000 adc r0, r0, r0

b070: 20433101 subcs r3, r3, r1, lsl #2

b074: e1530081 cmp r3, r1, lsl #1

b078: e0a00000 adc r0, r0, r0

b07c: 20433081 subcs r3, r3, r1, lsl #1

b080: e1530001 cmp r3, r1

b084: e0a00000 adc r0, r0, r0

b088: 20433001 subcs r3, r3, r1

b08c: e35c0000 cmp ip, #0

b090: 42600000 rsbmi r0, r0, #0

b094: e12fff1e bx lr

b098: e13c0000 teq ip, r0

b09c: 42600000 rsbmi r0, r0, #0

b0a0: e12fff1e bx lr

b0a4: 33a00000 movcc r0, #0

b0a8: 01a00fcc asreq r0, ip, #31

b0ac: 03800001 orreq r0, r0, #1

b0b0: e12fff1e bx lr

b0b4: e16f2f11 clz r2, r1

b0b8: e262201f rsb r2, r2, #31

b0bc: e35c0000 cmp ip, #0

b0c0: e1a00233 lsr r0, r3, r2

b0c4: 42600000 rsbmi r0, r0, #0

b0c8: e12fff1e bx lr

b0cc: e3500000 cmp r0, #0

b0d0: c3e00102 mvngt r0, #-2147483648 ; 0x80000000

b0d4: b3a00102 movlt r0, #-2147483648 ; 0x80000000

b0d8: ea000007 b b0fc <__aeabi_idiv0>

00008ae4 <main>:

[…]

8dbc: e3a01000 mov r1, #0

8dc0: e3a00001 mov r0, #1

8dc4: eb00083c bl aebc <__aeabi_idiv>

From:	Berat, Frederic (ADITG/SW1)
Subject:	[Libunwind-devel] Unwinding on arm and division by zero
Date:	Mon, 16 Mar 2015 15:54:50 +0000