diff mbox series

[13/17] powerpc: copy_thread add a back chain to the switch stack frame

Message ID 20221127124942.1665522-14-npiggin@gmail.com (mailing list archive)
State Accepted
Commit edbd0387f3249cc7e102f86d4852a9a9f3bb1305
Headers show
Series powerpc: Remove STACK_FRAME_OVERHEAD | expand

Commit Message

Nicholas Piggin Nov. 27, 2022, 12:49 p.m. UTC 
Stack unwinders need LR and the back chain as a minimum. The switch
stack uses regs->nip for its return pointer rather than lrsave, so
that was not set in the fork frame, and neither was the back chain.
This change sets those fields in the stack.

With this and the previous change, a stack trace in the switch or
interrupt stack goes from looking like this:

  Oops: Exception in kernel mode, sig: 5 [#1]
  LE PAGE_SIZE=64K MMU=Radix SMP NR_CPUS=2048 NUMA pSeries
  Modules linked in:
  CPU: 3 PID: 90 Comm: systemd Not tainted
  NIP:  c000000000011060 LR: c000000000010f68 CTR: 0000000000007fff
  [ ... regs ... ]
  NIP [c000000000011060] _switch+0x160/0x17c
  LR [c000000000010f68] _switch+0x68/0x17c
  Call Trace:

To this:

  Oops: Exception in kernel mode, sig: 5 [#1]
  LE PAGE_SIZE=64K MMU=Radix SMP NR_CPUS=2048 NUMA pSeries
  CPU: 0 PID: 93 Comm: systemd Not tainted
  NIP:  c000000000011060 LR: c000000000010f68 CTR: 0000000000007fff
  [ ... regs ... ]
  NIP [c000000000011060] _switch+0x160/0x17c
  LR [c000000000010f68] _switch+0x68/0x17c
  Call Trace:
  [c000000005a93e10] [c00000000000cdbc] ret_from_fork_scv+0x0/0x54
  --- interrupt: 3000 at 0x7fffa72f56d8
  NIP:  00007fffa72f56d8 LR: 0000000000000000 CTR: 0000000000000000
  [ ... regs ... ]
  NIP [00007fffa72f56d8] 0x7fffa72f56d8
  LR [0000000000000000] 0x0
  --- interrupt: 3000

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
 arch/powerpc/kernel/process.c | 2 ++
 1 file changed, 2 insertions(+)
diff mbox series

Patch

diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 27956831fa5d..6cb3982a11ef 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -1781,7 +1781,9 @@  int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
 	 * do some house keeping and then return from the fork or clone
 	 * system call, using the stack frame created above.
 	 */
+	((unsigned long *)sp)[STACK_FRAME_LR_SAVE] = (unsigned long)f;
 	sp -= STACK_SWITCH_FRAME_SIZE;
+	((unsigned long *)sp)[0] = sp + STACK_SWITCH_FRAME_SIZE;
 	kregs = (struct pt_regs *)(sp + STACK_SWITCH_FRAME_REGS);
 	p->thread.ksp = sp;