Commit 63be1a81 authored by Naveen N. Rao's avatar Naveen N. Rao Committed by Michael Ellerman

Revert "powerpc64/elfv1: Only dereference function descriptor for non-text symbols"

This reverts commit 83e840c7 ("powerpc64/elfv1: Only dereference
function descriptor for non-text symbols").

Chandan reported that on newer kernels, trying to enable function_graph
tracer on ppc64 (BE) locks up the system with the following trace:

  Unable to handle kernel paging request for data at address 0x600000002fa30010
  Faulting instruction address: 0xc0000000001f1300
  Thread overran stack, or stack corrupted
  Oops: Kernel access of bad area, sig: 11 [#1]
  Modules linked in:
  CPU: 1 PID: 6586 Comm: bash Not tainted 4.14.0-rc3-00162-g6e51f1f-dirty #20
  task: c000000625c07200 task.stack: c000000625c07310
  NIP:  c0000000001f1300 LR: c000000000121cac CTR: c000000000061af8
  REGS: c000000625c088c0 TRAP: 0380   Not tainted  (4.14.0-rc3-00162-g6e51f1f-dirty)
  MSR:  8000000000001032 <SF,ME,IR,DR,RI>  CR: 28002848  XER: 00000000
  CFAR: c0000000001f1320 SOFTE: 0
  NIP [c0000000001f1300] .__is_insn_slot_addr+0x30/0x90
  LR [c000000000121cac] .kernel_text_address+0x18c/0x1c0
  Call Trace:
  [c000000625c08b40] [c0000000001bd040] .is_module_text_address+0x20/0x40 (unreliable)
  [c000000625c08bc0] [c000000000121cac] .kernel_text_address+0x18c/0x1c0
  [c000000625c08c50] [c000000000061960] .prepare_ftrace_return+0x50/0x130
  [c000000625c08cf0] [c000000000061b10] .ftrace_graph_caller+0x14/0x34
  [c000000625c08d60] [c000000000121b40] .kernel_text_address+0x20/0x1c0
  [c000000625c08df0] [c000000000061960] .prepare_ftrace_return+0x50/0x130
  [c000000625c0ab30] [c000000000061960] .prepare_ftrace_return+0x50/0x130
  [c000000625c0abd0] [c000000000061b10] .ftrace_graph_caller+0x14/0x34
  [c000000625c0ac40] [c000000000121b40] .kernel_text_address+0x20/0x1c0
  [c000000625c0acd0] [c000000000061960] .prepare_ftrace_return+0x50/0x130
  [c000000625c0ad70] [c000000000061b10] .ftrace_graph_caller+0x14/0x34
  [c000000625c0ade0] [c000000000121b40] .kernel_text_address+0x20/0x1c0

This is because ftrace is using ppc_function_entry() for obtaining the
address of return_to_handler() in prepare_ftrace_return(). The call to
kernel_text_address() itself gets traced and we end up in a recursive

Fixes: 83e840c7 ("powerpc64/elfv1: Only dereference function descriptor for non-text symbols")
Cc: # v4.13+
Reported-by: default avatarChandan Rajendra <>
Signed-off-by: default avatarNaveen N. Rao <>
Signed-off-by: default avatarMichael Ellerman <>
parent 26e53d5e
......@@ -83,16 +83,8 @@ static inline unsigned long ppc_function_entry(void *func)
* On PPC64 ABIv1 the function pointer actually points to the
* function's descriptor. The first entry in the descriptor is the
* address of the function text.
* However, we may also receive pointer to an assembly symbol. To
* detect that, we first check if the function pointer we receive
* already points to kernel/module text and we only dereference it
* if it doesn't.
if (kernel_text_address((unsigned long)func))
return (unsigned long)func;
return ((func_descr_t *)func)->entry;
return ((func_descr_t *)func)->entry;
return (unsigned long)func;
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