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| author | Anton Blanchard <anton@samba.org> | 2014-10-13 10:41:38 +0200 |
|---|---|---|
| committer | Michael Ellerman <mpe@ellerman.id.au> | 2014-10-15 02:23:19 +0200 |
| commit | bfe9a2cfe91a1c920f152ce5fd0a9ad74b3daf12 (patch) | |
| tree | ff5f5b9cd9db51252e08ae41f8f5d751117a8fdf /arch/powerpc/include/asm/perf_event.h | |
| parent | powerpc/numa: Add ability to disable and debug topology updates (diff) | |
| download | linux-bfe9a2cfe91a1c920f152ce5fd0a9ad74b3daf12.tar.xz linux-bfe9a2cfe91a1c920f152ce5fd0a9ad74b3daf12.zip | |
powerpc: Reimplement __get_SP() as a function not a define
Li Zhong points out an issue with our current __get_SP()
implementation. If ftrace function tracing is enabled (ie -pg
profiling using _mcount) we spill a stack frame on 64bit all the
time.
If a function calls __get_SP() and later calls a function that is
tail call optimised, we will pop the stack frame and the value
returned by __get_SP() is no longer valid. An example from Li can
be found in save_stack_trace -> save_context_stack:
c0000000000432c0 <.save_stack_trace>:
c0000000000432c0: mflr r0
c0000000000432c4: std r0,16(r1)
c0000000000432c8: stdu r1,-128(r1) <-- stack frame for _mcount
c0000000000432cc: std r3,112(r1)
c0000000000432d0: bl <._mcount>
c0000000000432d4: nop
c0000000000432d8: mr r4,r1 <-- __get_SP()
c0000000000432dc: ld r5,632(r13)
c0000000000432e0: ld r3,112(r1)
c0000000000432e4: li r6,1
c0000000000432e8: addi r1,r1,128 <-- pop stack frame
c0000000000432ec: ld r0,16(r1)
c0000000000432f0: mtlr r0
c0000000000432f4: b <.save_context_stack> <-- tail call optimized
save_context_stack ends up with a stack pointer below the current
one, and it is likely to be scribbled over.
Fix this by making __get_SP() a function which returns the
callers stack frame. Also replace inline assembly which grabs
the stack pointer in save_stack_trace and show_stack with
__get_SP().
This also fixes an issue with perf_arch_fetch_caller_regs().
It currently unwinds the stack once, which will skip a
valid stack frame on a leaf function. With the __get_SP() fixes
in this patch, we never need to unwind the stack frame to get
to the first interesting frame.
We have to export __get_SP() because perf_arch_fetch_caller_regs()
(which is used in modules) calls it from a header file.
Reported-by: Li Zhong <zhong@linux.vnet.ibm.com>
Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Diffstat (limited to 'arch/powerpc/include/asm/perf_event.h')
| -rw-r--r-- | arch/powerpc/include/asm/perf_event.h | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/arch/powerpc/include/asm/perf_event.h b/arch/powerpc/include/asm/perf_event.h index 0bb23725b1e7..b058568a850d 100644 --- a/arch/powerpc/include/asm/perf_event.h +++ b/arch/powerpc/include/asm/perf_event.h @@ -34,7 +34,7 @@ do { \ (regs)->result = 0; \ (regs)->nip = __ip; \ - (regs)->gpr[1] = *(unsigned long *)__get_SP(); \ + (regs)->gpr[1] = __get_SP(); \ asm volatile("mfmsr %0" : "=r" ((regs)->msr)); \ } while (0) #endif |