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== Comment: #0 - Pedro Miraglia Franco de Carval <pedro...@br.ibm.com> -
2017-06-30 12:52:06 ==
After setting a hardware watchpoint on a variable through gdb, the traced
process gets stuck on the instruction that affects the watched address but
doesn't stop.
Steps to reproduce:
Make a program to be traced:
pedromfc@perch:~$ cat wp_test.c
int my_global = 0;
void main( void ) {
my_global = 1;
}
pedromfc@perch:~$ gcc -g -O0 -o wp_test wp_test.c
Debug the binary:
pedromfc@perch:~$ gdb -q wp_test
Reading symbols from wp_test...done.
(gdb) watch my_global
Hardware watchpoint 1: my_global
(gdb) run
Starting program: /home/pedromfc/wp_test
[Program stuck here, manually interrupt]
^C
Program received signal SIGINT, Interrupt.
0x00000000200007a0 in main () at wp_test.c:4
4 my_global = 1;
(gdb) disas
Dump of assembler code for function main:
0x0000000020000780 <+0>: addis r2,r12,2
0x0000000020000784 <+4>: addi r2,r2,30592
0x0000000020000788 <+8>: std r31,-8(r1)
0x000000002000078c <+12>: stdu r1,-48(r1)
0x0000000020000790 <+16>: mr r31,r1
0x0000000020000794 <+20>: nop
0x0000000020000798 <+24>: addi r9,r2,-32492
0x000000002000079c <+28>: li r10,1
=> 0x00000000200007a0 <+32>: stw r10,0(r9)
0x00000000200007a4 <+36>: nop
0x00000000200007a8 <+40>: addi r1,r31,48
0x00000000200007ac <+44>: ld r31,-8(r1)
0x00000000200007b0 <+48>: blr
0x00000000200007b4 <+52>: .long 0x0
0x00000000200007b8 <+56>: .long 0x0
0x00000000200007bc <+60>: .long 0x1000180
End of assembler dump.
(gdb) info reg r9
r9 0x20020014 537002004
(gdb) p /x &my_global
$1 = 0x20020014
(gdb) continue
Continuing.
[Like before, nothing happens]
^C
Program received signal SIGINT, Interrupt.
0x00000000200007a0 in main () at wp_test.c:4
4 my_global = 1;
(gdb) disass
Dump of assembler code for function main:
0x0000000020000780 <+0>: addis r2,r12,2
0x0000000020000784 <+4>: addi r2,r2,30592
0x0000000020000788 <+8>: std r31,-8(r1)
0x000000002000078c <+12>: stdu r1,-48(r1)
0x0000000020000790 <+16>: mr r31,r1
0x0000000020000794 <+20>: nop
0x0000000020000798 <+24>: addi r9,r2,-32492
0x000000002000079c <+28>: li r10,1
=> 0x00000000200007a0 <+32>: stw r10,0(r9)
0x00000000200007a4 <+36>: nop
0x00000000200007a8 <+40>: addi r1,r31,48
0x00000000200007ac <+44>: ld r31,-8(r1)
0x00000000200007b0 <+48>: blr
0x00000000200007b4 <+52>: .long 0x0
0x00000000200007b8 <+56>: .long 0x0
0x00000000200007bc <+60>: .long 0x1000180
End of assembler dump.
(gdb) continue
Continuing.
Check on another terminal that the program is running (but stuck in the
same instruction):
pedromfc@perch:~$ ps -C gdb,wp_test -o pid,comm,state
PID COMMAND S
19178 gdb S
19193 wp_test R
This happened on this machine model:
cpu : POWER9 (raw), altivec supported
revision : 1.0 (pvr 004e 0100)
machine : PowerNV 8375-42A
firmware : OPAL
SN : 13C665W
With this kernel:
pedromfc@perch:~$ uname -a
Linux perch 4.10.0-19-generic #21-Ubuntu SMP Thu Apr 6 17:03:05 UTC 2017
ppc64le ppc64le ppc64le GNU/Linux
It also happened with this kernel, on another machine:
[pedromfc@zzfp342p1 ~]$ uname -a
Linux zzfp342p1 4.11.0-10.el7a.ppc64le #1 SMP Wed Jun 21 20:50:21 EDT 2017
ppc64le ppc64le ppc64le GNU/Linux
On another machine (P8) the watchpoint triggers as expected and the
process stops immediately after the store instruction:
pedromfc@genoa:~$ uname -a
Linux genoa 3.13.0-35-generic #62-Ubuntu SMP Fri Aug 15 01:57:29 UTC 2014
ppc64le ppc64le ppc64le GNU/Linux
pedromfc@genoa:~$ gdb wp_test
...
Reading symbols from wp_test...done.
(gdb) watch my_global
Hardware watchpoint 1: my_global
(gdb) run
Starting program: /home/pedromfc/wp_test
Hardware watchpoint 1: my_global
Old value = 0
New value = 1
main () at wp_test.c:5
5 }
(gdb)
https://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux.git/commit/?id=d89ba5353f301971dd7d2f9fdf25c4432728f38e
** Affects: linux (Ubuntu)
Importance: Undecided
Assignee: Ubuntu on IBM Power Systems Bug Triage (ubuntu-power-triage)
Status: New
** Tags: architecture-ppc64le bugnameltc-156292 severity-medium
targetmilestone-inin1704
--
Process hangs on HW watchpoint on Power9
https://bugs.launchpad.net/bugs/1708451
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