58b69401c7
Function tracing is currently broken for all 32 bit MIPS platforms.
When tracing is enabled, the kernel immediately hangs on boot.
This is a result of commit b732d439cb
that changes the kernel/trace/Kconfig file so that is no longer
forces FRAME_POINTER when FUNCTION_TRACING is enabled.
MIPS frame pointers are generally considered to be useless because
they cannot be used to unwind the stack. Unfortunately the MIPS
function tracing code has bugs that are masked by the use of frame
pointers. This commit fixes the bugs so that MIPS frame pointers
don't need to be enabled.
The bugs are a result of the odd calling sequence used to call the trace
routine. This calling sequence is inserted into every traceable function
when the tracing CONFIG option is enabled. This sequence is generated
for 32bit MIPS platforms by the compiler via the "-pg" flag.
Part of the sequence is "addiu sp,sp,-8" in the delay slot after every
call to the trace routine "_mcount" (some legacy thing where 2 arguments
used to be pushed on the stack). The _mcount routine is expected to
adjust the sp by +8 before returning. So when not disabled, the original
jalr and addiu will be there, so _mcount has to adjust sp.
The problem is that when tracing is disabled for a function, the
"jalr _mcount" instruction is replaced with a nop, but the
"addiu sp,sp,-8" is still executed and the stack pointer is left
trashed. When frame pointers are enabled the problem is masked
because any access to the stack is done through the frame
pointer and the stack pointer is restored from the frame pointer when
the function returns.
This patch writes two nops starting at the address of the "jalr _mcount"
instruction whenever tracing is disabled. This means that the
"addiu sp,sp.-8" will be converted to a nop along with the "jalr". When
disabled, there will be two nops.
This is SMP safe because the first time this happens is during
ftrace_init() which is before any other processor has been started.
Subsequent calls to enable/disable tracing when other CPUs ARE running
will still be safe because the enable will only change the first nop
to a "jalr" and the disable, while writing 2 nops, will only be changing
the "jalr". This patch also stops using stop_machine() to call the
tracer enable/disable routines and calls them directly because the
routines are SMP safe.
When the kernel first boots we have to be able to handle the gcc
generated jalr, addui sequence until ftrace_init gets a chance to run
and change the sequence. At this point mcount just adjusts the stack
and returns. When ftrace_init runs, we convert the jalr/addui to nops.
Then whenever tracing is enabled we convert the first nop to a "jalr
mcount+8". The mcount+8 entry point skips the stack adjust.
[ralf@linux-mips.org: Folded in Steven Rostedt's build fix.]
Signed-off-by: Al Cooper <alcooperx@gmail.com>
Cc: rostedt@goodmis.org
Cc: ddaney.cavm@gmail.com
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/4806/
Patchwork: https://patchwork.linux-mips.org/patch/4841/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
204 lines
4.0 KiB
ArmAsm
204 lines
4.0 KiB
ArmAsm
/*
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* MIPS specific _mcount support
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*
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* This file is subject to the terms and conditions of the GNU General Public
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* License. See the file "COPYING" in the main directory of this archive for
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* more details.
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*
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* Copyright (C) 2009 Lemote Inc. & DSLab, Lanzhou University, China
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* Copyright (C) 2010 DSLab, Lanzhou University, China
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* Author: Wu Zhangjin <wuzhangjin@gmail.com>
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*/
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#include <asm/regdef.h>
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#include <asm/stackframe.h>
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#include <asm/ftrace.h>
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.text
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.set noreorder
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.set noat
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.macro MCOUNT_SAVE_REGS
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PTR_SUBU sp, PT_SIZE
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PTR_S ra, PT_R31(sp)
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PTR_S AT, PT_R1(sp)
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PTR_S a0, PT_R4(sp)
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PTR_S a1, PT_R5(sp)
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PTR_S a2, PT_R6(sp)
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PTR_S a3, PT_R7(sp)
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#ifdef CONFIG_64BIT
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PTR_S a4, PT_R8(sp)
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PTR_S a5, PT_R9(sp)
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PTR_S a6, PT_R10(sp)
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PTR_S a7, PT_R11(sp)
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#endif
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.endm
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.macro MCOUNT_RESTORE_REGS
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PTR_L ra, PT_R31(sp)
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PTR_L AT, PT_R1(sp)
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PTR_L a0, PT_R4(sp)
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PTR_L a1, PT_R5(sp)
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PTR_L a2, PT_R6(sp)
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PTR_L a3, PT_R7(sp)
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#ifdef CONFIG_64BIT
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PTR_L a4, PT_R8(sp)
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PTR_L a5, PT_R9(sp)
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PTR_L a6, PT_R10(sp)
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PTR_L a7, PT_R11(sp)
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#else
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PTR_ADDIU sp, PT_SIZE
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#endif
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.endm
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.macro RETURN_BACK
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jr ra
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move ra, AT
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.endm
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/*
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* The -mmcount-ra-address option of gcc 4.5 uses register $12 to pass
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* the location of the parent's return address.
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*/
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#define MCOUNT_RA_ADDRESS_REG $12
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#ifdef CONFIG_DYNAMIC_FTRACE
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NESTED(ftrace_caller, PT_SIZE, ra)
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.globl _mcount
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_mcount:
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b ftrace_stub
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addiu sp,sp,8
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/* When tracing is activated, it calls ftrace_caller+8 (aka here) */
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lw t1, function_trace_stop
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bnez t1, ftrace_stub
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nop
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MCOUNT_SAVE_REGS
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#ifdef KBUILD_MCOUNT_RA_ADDRESS
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PTR_S MCOUNT_RA_ADDRESS_REG, PT_R12(sp)
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#endif
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move a0, ra /* arg1: self return address */
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.globl ftrace_call
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ftrace_call:
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nop /* a placeholder for the call to a real tracing function */
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move a1, AT /* arg2: parent's return address */
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#ifdef CONFIG_FUNCTION_GRAPH_TRACER
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.globl ftrace_graph_call
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ftrace_graph_call:
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nop
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nop
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#endif
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MCOUNT_RESTORE_REGS
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.globl ftrace_stub
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ftrace_stub:
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RETURN_BACK
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END(ftrace_caller)
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#else /* ! CONFIG_DYNAMIC_FTRACE */
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NESTED(_mcount, PT_SIZE, ra)
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lw t1, function_trace_stop
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bnez t1, ftrace_stub
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nop
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PTR_LA t1, ftrace_stub
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PTR_L t2, ftrace_trace_function /* Prepare t2 for (1) */
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bne t1, t2, static_trace
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nop
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#ifdef CONFIG_FUNCTION_GRAPH_TRACER
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PTR_L t3, ftrace_graph_return
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bne t1, t3, ftrace_graph_caller
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nop
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PTR_LA t1, ftrace_graph_entry_stub
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PTR_L t3, ftrace_graph_entry
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bne t1, t3, ftrace_graph_caller
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nop
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#endif
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b ftrace_stub
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nop
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static_trace:
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MCOUNT_SAVE_REGS
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move a0, ra /* arg1: self return address */
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jalr t2 /* (1) call *ftrace_trace_function */
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move a1, AT /* arg2: parent's return address */
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MCOUNT_RESTORE_REGS
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.globl ftrace_stub
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ftrace_stub:
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RETURN_BACK
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END(_mcount)
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#endif /* ! CONFIG_DYNAMIC_FTRACE */
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#ifdef CONFIG_FUNCTION_GRAPH_TRACER
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NESTED(ftrace_graph_caller, PT_SIZE, ra)
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#ifndef CONFIG_DYNAMIC_FTRACE
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MCOUNT_SAVE_REGS
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#endif
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/* arg1: Get the location of the parent's return address */
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#ifdef KBUILD_MCOUNT_RA_ADDRESS
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#ifdef CONFIG_DYNAMIC_FTRACE
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PTR_L a0, PT_R12(sp)
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#else
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move a0, MCOUNT_RA_ADDRESS_REG
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#endif
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bnez a0, 1f /* non-leaf func: stored in MCOUNT_RA_ADDRESS_REG */
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nop
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#endif
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PTR_LA a0, PT_R1(sp) /* leaf func: the location in current stack */
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1:
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/* arg2: Get self return address */
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#ifdef CONFIG_DYNAMIC_FTRACE
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PTR_L a1, PT_R31(sp)
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#else
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move a1, ra
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#endif
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/* arg3: Get frame pointer of current stack */
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#ifdef CONFIG_FRAME_POINTER
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move a2, fp
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#else /* ! CONFIG_FRAME_POINTER */
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#ifdef CONFIG_64BIT
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PTR_LA a2, PT_SIZE(sp)
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#else
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PTR_LA a2, (PT_SIZE+8)(sp)
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#endif
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#endif
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jal prepare_ftrace_return
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nop
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MCOUNT_RESTORE_REGS
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RETURN_BACK
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END(ftrace_graph_caller)
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.align 2
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.globl return_to_handler
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return_to_handler:
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PTR_SUBU sp, PT_SIZE
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PTR_S v0, PT_R2(sp)
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jal ftrace_return_to_handler
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PTR_S v1, PT_R3(sp)
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/* restore the real parent address: v0 -> ra */
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move ra, v0
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PTR_L v0, PT_R2(sp)
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PTR_L v1, PT_R3(sp)
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jr ra
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PTR_ADDIU sp, PT_SIZE
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#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
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.set at
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.set reorder
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