bfe9a2cfe9
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later calls a function that is tail call optimised, we will pop the stack frame and the value returned by __get_SP() is no longer valid.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>
41 lines
1.2 KiB
C
41 lines
1.2 KiB
C
/*
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* Performance event support - hardware-specific disambiguation
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*
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* For now this is a compile-time decision, but eventually it should be
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* runtime. This would allow multiplatform perf event support for e300 (fsl
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* embedded perf counters) plus server/classic, and would accommodate
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* devices other than the core which provide their own performance counters.
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*
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* Copyright 2010 Freescale Semiconductor, Inc.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version
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* 2 of the License, or (at your option) any later version.
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*/
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#ifdef CONFIG_PPC_PERF_CTRS
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#include <asm/perf_event_server.h>
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#endif
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#ifdef CONFIG_FSL_EMB_PERF_EVENT
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#include <asm/perf_event_fsl_emb.h>
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#endif
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#ifdef CONFIG_PERF_EVENTS
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#include <asm/ptrace.h>
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#include <asm/reg.h>
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/*
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* Overload regs->result to specify whether we should use the MSR (result
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* is zero) or the SIAR (result is non zero).
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*/
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#define perf_arch_fetch_caller_regs(regs, __ip) \
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do { \
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(regs)->result = 0; \
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(regs)->nip = __ip; \
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(regs)->gpr[1] = __get_SP(); \
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asm volatile("mfmsr %0" : "=r" ((regs)->msr)); \
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} while (0)
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#endif
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