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From: Nicholas Piggin <npiggin@gmail.com>
To: linuxppc-dev@lists.ozlabs.org
Cc: Nicholas Piggin <npiggin@gmail.com>
Subject: [PATCH 13/17] powerpc: copy_thread add a back chain to the switch stack frame
Date: Sun, 27 Nov 2022 22:49:38 +1000	[thread overview]
Message-ID: <20221127124942.1665522-14-npiggin@gmail.com> (raw)
In-Reply-To: <20221127124942.1665522-1-npiggin@gmail.com>

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 --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;
 
-- 
2.37.2


  parent reply	other threads:[~2022-11-27 13:02 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-11-27 12:49 [PATCH 00/17] powerpc: Remove STACK_FRAME_OVERHEAD Nicholas Piggin
2022-11-27 12:49 ` [PATCH 01/17] KVM: PPC: Book3E: Fix CONFIG_TRACE_IRQFLAGS support Nicholas Piggin
2022-11-27 12:49 ` [PATCH 02/17] powerpc/64: Remove asm interrupt tracing call helpers Nicholas Piggin
2022-11-27 12:49 ` [PATCH 03/17] powerpc/perf: callchain validate kernel stack pointer bounds Nicholas Piggin
2022-11-27 12:49 ` [PATCH 04/17] powerpc: Rearrange copy_thread child stack creation Nicholas Piggin
2022-11-27 12:49 ` [PATCH 05/17] powerpc/pseries: hvcall stack frame overhead Nicholas Piggin
2022-11-27 12:49 ` [PATCH 06/17] powerpc: simplify ppc_save_regs Nicholas Piggin
2022-11-27 12:49 ` [PATCH 07/17] powerpc: add definition for pt_regs offset within an interrupt frame Nicholas Piggin
2022-11-27 12:49 ` [PATCH 08/17] powerpc: add a definition for the marker offset within the " Nicholas Piggin
2022-11-27 12:49 ` [PATCH 09/17] powerpc: Rename STACK_FRAME_MARKER and derive it from frame offset Nicholas Piggin
2022-11-27 12:49 ` [PATCH 10/17] powerpc: add a define for the user interrupt frame size Nicholas Piggin
2022-11-27 12:49 ` [PATCH 11/17] powerpc: add a define for the switch frame size and regs offset Nicholas Piggin
2022-11-27 12:49 ` [PATCH 12/17] powerpc: copy_thread fill in interrupt frame marker and back chain Nicholas Piggin
2022-11-27 12:49 ` Nicholas Piggin [this message]
2022-11-27 12:49 ` [PATCH 14/17] powerpc: split validate_sp into two functions Nicholas Piggin
2022-11-27 12:49 ` [PATCH 15/17] powerpc: allow minimum sized kernel stack frames Nicholas Piggin
2022-11-27 12:49 ` [PATCH 16/17] powerpc/64: ELFv2 use minimal stack frames in int and switch frame sizes Nicholas Piggin
2022-11-27 12:49 ` [PATCH 17/17] powerpc: remove STACK_FRAME_OVERHEAD Nicholas Piggin
2022-12-08 12:40 ` [PATCH 00/17] powerpc: Remove STACK_FRAME_OVERHEAD Michael Ellerman

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