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562e14f722
There's two methods of enabling function tracing in Linux on x86. One is with just "gcc -pg" and the other is "gcc -pg -mfentry". The former will use calls to a special function "mcount" after the frame is set up in all C functions. The latter will add calls to a special function called "fentry" as the very first instruction of all C functions. At compile time, there is a check to see if gcc supports, -mfentry, and if it does, it will use that, because it is more versatile and less error prone for function tracing. Starting with v4.19, the minimum gcc supported to build the Linux kernel, was raised to version 4.6. That also happens to be the first gcc version to support -mfentry. Since on x86, using gcc versions from 4.6 and beyond will unconditionally enable the -mfentry, it will no longer use mcount as the method for inserting calls into the C functions of the kernel. This means that there is no point in continuing to maintain mcount in x86. Remove support for using mcount. This makes the code less complex, and will also allow it to be simplified in the future. Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Jiri Kosina <jkosina@suse.cz> Acked-by: Josh Poimboeuf <jpoimboe@redhat.com> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
313 lines
7.3 KiB
ArmAsm
313 lines
7.3 KiB
ArmAsm
/* SPDX-License-Identifier: GPL-2.0 */
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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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#include <asm/export.h>
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#include <asm/nospec-branch.h>
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#include <asm/unwind_hints.h>
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.code64
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.section .entry.text, "ax"
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# define function_hook __fentry__
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EXPORT_SYMBOL(__fentry__)
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#ifdef CONFIG_FRAME_POINTER
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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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/* No need to save a stack frame */
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# define MCOUNT_FRAME_SIZE 0
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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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#ifdef CONFIG_FRAME_POINTER
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/* Save the original rbp */
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pushq %rbp
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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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/* 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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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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#ifdef CONFIG_FRAME_POINTER
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movq MCOUNT_REG_SIZE-8(%rsp), %rdx
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#else
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movq %rbp, %rdx
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#endif
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movq %rdx, RBP(%rsp)
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/* Copy the parent address into %rsi (second parameter) */
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movq MCOUNT_REG_SIZE+8+\added(%rsp), %rsi
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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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ENDPROC(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 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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/*
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* This is weak to keep gas from relaxing the jumps.
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* It is also used to copy the retq for trampolines.
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*/
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WEAK(ftrace_stub)
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retq
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ENDPROC(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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ENDPROC(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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movq ftrace_trace_function, %r8
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CALL_NOSPEC %r8
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restore_mcount_regs
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jmp fgraph_trace
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ENDPROC(function_hook)
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#endif /* CONFIG_DYNAMIC_FTRACE */
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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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leaq MCOUNT_REG_SIZE+8(%rsp), %rsi
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movq $0, %rdx /* No framepointers needed */
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call prepare_ftrace_return
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restore_mcount_regs
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retq
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ENDPROC(ftrace_graph_caller)
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ENTRY(return_to_handler)
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UNWIND_HINT_EMPTY
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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_NOSPEC %rdi
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END(return_to_handler)
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#endif
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