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8329e818f1
Matt Fleming reported seeing crashes when enabling and disabling
function profiling which uses function graph tracer. Later Namhyung Kim
hit a similar issue and he found that the issue was due to the jmp to
ftrace_stub in ftrace_graph_call was only two bytes, and when it was
changed to jump to the tracing code, it overwrote the ftrace_stub that
was after it.
Masami Hiramatsu bisected this down to a binutils change:
8dcea93252a9ea7dff57e85220a719e2a5e8ab41 is the first bad commit
commit 8dcea93252a9ea7dff57e85220a719e2a5e8ab41
Author: H.J. Lu <hjl.tools@gmail.com>
Date: Fri May 15 03:17:31 2015 -0700
Add -mshared option to x86 ELF assembler
This patch adds -mshared option to x86 ELF assembler. By default,
assembler will optimize out non-PLT relocations against defined non-weak
global branch targets with default visibility. The -mshared option tells
the assembler to generate code which may go into a shared library
where all non-weak global branch targets with default visibility can
be preempted. The resulting code is slightly bigger. This option
only affects the handling of branch instructions.
Declaring ftrace_stub as a weak call prevents gas from using two byte
jumps to it, which would be converted to a jump to the function graph
code.
Link: http://lkml.kernel.org/r/20160516230035.1dbae571@gandalf.local.home
Reported-by: Matt Fleming <matt@codeblueprint.co.uk>
Reported-by: Namhyung Kim <namhyung@kernel.org>
Tested-by: Matt Fleming <matt@codeblueprint.co.uk>
Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
336 lines
7.9 KiB
ArmAsm
336 lines
7.9 KiB
ArmAsm
/*
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* linux/arch/x86_64/mcount_64.S
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*
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* Copyright (C) 2014 Steven Rostedt, Red Hat Inc
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*/
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#include <linux/linkage.h>
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#include <asm/ptrace.h>
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#include <asm/ftrace.h>
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.code64
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.section .entry.text, "ax"
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#ifdef CONFIG_FUNCTION_TRACER
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#ifdef CC_USING_FENTRY
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# define function_hook __fentry__
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#else
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# define function_hook mcount
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#endif
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/* All cases save the original rbp (8 bytes) */
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#ifdef CONFIG_FRAME_POINTER
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# ifdef CC_USING_FENTRY
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/* Save parent and function stack frames (rip and rbp) */
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# define MCOUNT_FRAME_SIZE (8+16*2)
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# else
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/* Save just function stack frame (rip and rbp) */
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# define MCOUNT_FRAME_SIZE (8+16)
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# endif
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#else
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/* No need to save a stack frame */
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# define MCOUNT_FRAME_SIZE 8
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#endif /* CONFIG_FRAME_POINTER */
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/* Size of stack used to save mcount regs in save_mcount_regs */
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#define MCOUNT_REG_SIZE (SS+8 + MCOUNT_FRAME_SIZE)
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/*
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* gcc -pg option adds a call to 'mcount' in most functions.
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* When -mfentry is used, the call is to 'fentry' and not 'mcount'
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* and is done before the function's stack frame is set up.
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* They both require a set of regs to be saved before calling
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* any C code and restored before returning back to the function.
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*
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* On boot up, all these calls are converted into nops. When tracing
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* is enabled, the call can jump to either ftrace_caller or
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* ftrace_regs_caller. Callbacks (tracing functions) that require
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* ftrace_regs_caller (like kprobes) need to have pt_regs passed to
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* it. For this reason, the size of the pt_regs structure will be
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* allocated on the stack and the required mcount registers will
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* be saved in the locations that pt_regs has them in.
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*/
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/*
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* @added: the amount of stack added before calling this
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*
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* After this is called, the following registers contain:
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*
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* %rdi - holds the address that called the trampoline
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* %rsi - holds the parent function (traced function's return address)
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* %rdx - holds the original %rbp
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*/
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.macro save_mcount_regs added=0
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/* Always save the original rbp */
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pushq %rbp
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#ifdef CONFIG_FRAME_POINTER
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/*
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* Stack traces will stop at the ftrace trampoline if the frame pointer
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* is not set up properly. If fentry is used, we need to save a frame
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* pointer for the parent as well as the function traced, because the
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* fentry is called before the stack frame is set up, where as mcount
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* is called afterward.
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*/
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#ifdef CC_USING_FENTRY
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/* Save the parent pointer (skip orig rbp and our return address) */
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pushq \added+8*2(%rsp)
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pushq %rbp
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movq %rsp, %rbp
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/* Save the return address (now skip orig rbp, rbp and parent) */
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pushq \added+8*3(%rsp)
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#else
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/* Can't assume that rip is before this (unless added was zero) */
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pushq \added+8(%rsp)
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#endif
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pushq %rbp
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movq %rsp, %rbp
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#endif /* CONFIG_FRAME_POINTER */
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/*
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* We add enough stack to save all regs.
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*/
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subq $(MCOUNT_REG_SIZE - MCOUNT_FRAME_SIZE), %rsp
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movq %rax, RAX(%rsp)
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movq %rcx, RCX(%rsp)
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movq %rdx, RDX(%rsp)
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movq %rsi, RSI(%rsp)
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movq %rdi, RDI(%rsp)
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movq %r8, R8(%rsp)
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movq %r9, R9(%rsp)
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/*
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* Save the original RBP. Even though the mcount ABI does not
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* require this, it helps out callers.
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*/
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movq MCOUNT_REG_SIZE-8(%rsp), %rdx
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movq %rdx, RBP(%rsp)
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/* Copy the parent address into %rsi (second parameter) */
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#ifdef CC_USING_FENTRY
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movq MCOUNT_REG_SIZE+8+\added(%rsp), %rsi
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#else
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/* %rdx contains original %rbp */
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movq 8(%rdx), %rsi
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#endif
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/* Move RIP to its proper location */
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movq MCOUNT_REG_SIZE+\added(%rsp), %rdi
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movq %rdi, RIP(%rsp)
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/*
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* Now %rdi (the first parameter) has the return address of
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* where ftrace_call returns. But the callbacks expect the
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* address of the call itself.
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*/
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subq $MCOUNT_INSN_SIZE, %rdi
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.endm
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.macro restore_mcount_regs
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movq R9(%rsp), %r9
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movq R8(%rsp), %r8
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movq RDI(%rsp), %rdi
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movq RSI(%rsp), %rsi
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movq RDX(%rsp), %rdx
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movq RCX(%rsp), %rcx
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movq RAX(%rsp), %rax
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/* ftrace_regs_caller can modify %rbp */
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movq RBP(%rsp), %rbp
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addq $MCOUNT_REG_SIZE, %rsp
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.endm
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#ifdef CONFIG_DYNAMIC_FTRACE
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ENTRY(function_hook)
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retq
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END(function_hook)
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ENTRY(ftrace_caller)
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/* save_mcount_regs fills in first two parameters */
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save_mcount_regs
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GLOBAL(ftrace_caller_op_ptr)
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/* Load the ftrace_ops into the 3rd parameter */
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movq function_trace_op(%rip), %rdx
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/* regs go into 4th parameter (but make it NULL) */
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movq $0, %rcx
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GLOBAL(ftrace_call)
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call ftrace_stub
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restore_mcount_regs
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/*
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* The copied trampoline must call ftrace_epilogue as it
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* still may need to call the function graph tracer.
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*
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* The code up to this label is copied into trampolines so
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* think twice before adding any new code or changing the
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* layout here.
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*/
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GLOBAL(ftrace_epilogue)
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#ifdef CONFIG_FUNCTION_GRAPH_TRACER
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GLOBAL(ftrace_graph_call)
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jmp ftrace_stub
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#endif
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/* This is weak to keep gas from relaxing the jumps */
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WEAK(ftrace_stub)
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retq
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END(ftrace_caller)
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ENTRY(ftrace_regs_caller)
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/* Save the current flags before any operations that can change them */
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pushfq
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/* added 8 bytes to save flags */
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save_mcount_regs 8
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/* save_mcount_regs fills in first two parameters */
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GLOBAL(ftrace_regs_caller_op_ptr)
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/* Load the ftrace_ops into the 3rd parameter */
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movq function_trace_op(%rip), %rdx
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/* Save the rest of pt_regs */
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movq %r15, R15(%rsp)
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movq %r14, R14(%rsp)
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movq %r13, R13(%rsp)
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movq %r12, R12(%rsp)
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movq %r11, R11(%rsp)
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movq %r10, R10(%rsp)
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movq %rbx, RBX(%rsp)
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/* Copy saved flags */
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movq MCOUNT_REG_SIZE(%rsp), %rcx
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movq %rcx, EFLAGS(%rsp)
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/* Kernel segments */
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movq $__KERNEL_DS, %rcx
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movq %rcx, SS(%rsp)
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movq $__KERNEL_CS, %rcx
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movq %rcx, CS(%rsp)
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/* Stack - skipping return address and flags */
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leaq MCOUNT_REG_SIZE+8*2(%rsp), %rcx
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movq %rcx, RSP(%rsp)
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/* regs go into 4th parameter */
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leaq (%rsp), %rcx
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GLOBAL(ftrace_regs_call)
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call ftrace_stub
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/* Copy flags back to SS, to restore them */
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movq EFLAGS(%rsp), %rax
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movq %rax, MCOUNT_REG_SIZE(%rsp)
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/* Handlers can change the RIP */
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movq RIP(%rsp), %rax
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movq %rax, MCOUNT_REG_SIZE+8(%rsp)
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/* restore the rest of pt_regs */
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movq R15(%rsp), %r15
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movq R14(%rsp), %r14
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movq R13(%rsp), %r13
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movq R12(%rsp), %r12
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movq R10(%rsp), %r10
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movq RBX(%rsp), %rbx
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restore_mcount_regs
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/* Restore flags */
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popfq
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/*
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* As this jmp to ftrace_epilogue can be a short jump
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* it must not be copied into the trampoline.
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* The trampoline will add the code to jump
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* to the return.
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*/
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GLOBAL(ftrace_regs_caller_end)
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jmp ftrace_epilogue
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END(ftrace_regs_caller)
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#else /* ! CONFIG_DYNAMIC_FTRACE */
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ENTRY(function_hook)
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cmpq $ftrace_stub, ftrace_trace_function
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jnz trace
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fgraph_trace:
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#ifdef CONFIG_FUNCTION_GRAPH_TRACER
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cmpq $ftrace_stub, ftrace_graph_return
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jnz ftrace_graph_caller
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cmpq $ftrace_graph_entry_stub, ftrace_graph_entry
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jnz ftrace_graph_caller
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#endif
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GLOBAL(ftrace_stub)
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retq
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trace:
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/* save_mcount_regs fills in first two parameters */
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save_mcount_regs
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/*
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* When DYNAMIC_FTRACE is not defined, ARCH_SUPPORTS_FTRACE_OPS is not
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* set (see include/asm/ftrace.h and include/linux/ftrace.h). Only the
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* ip and parent ip are used and the list function is called when
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* function tracing is enabled.
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*/
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call *ftrace_trace_function
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restore_mcount_regs
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jmp fgraph_trace
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END(function_hook)
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#endif /* CONFIG_DYNAMIC_FTRACE */
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#endif /* CONFIG_FUNCTION_TRACER */
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#ifdef CONFIG_FUNCTION_GRAPH_TRACER
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ENTRY(ftrace_graph_caller)
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/* Saves rbp into %rdx and fills first parameter */
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save_mcount_regs
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#ifdef CC_USING_FENTRY
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leaq MCOUNT_REG_SIZE+8(%rsp), %rsi
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movq $0, %rdx /* No framepointers needed */
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#else
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/* Save address of the return address of traced function */
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leaq 8(%rdx), %rsi
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/* ftrace does sanity checks against frame pointers */
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movq (%rdx), %rdx
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#endif
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call prepare_ftrace_return
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restore_mcount_regs
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retq
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END(ftrace_graph_caller)
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GLOBAL(return_to_handler)
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subq $24, %rsp
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/* Save the return values */
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movq %rax, (%rsp)
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movq %rdx, 8(%rsp)
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movq %rbp, %rdi
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call ftrace_return_to_handler
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movq %rax, %rdi
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movq 8(%rsp), %rdx
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movq (%rsp), %rax
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addq $24, %rsp
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jmp *%rdi
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#endif
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