linux/arch/x86/kernel/ftrace_64.S
Steven Rostedt (VMware) 562e14f722 ftrace/x86: Remove mcount support
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>
2019-05-10 12:33:09 -04:00

314 lines
7.3 KiB
ArmAsm

/* SPDX-License-Identifier: GPL-2.0 */
/*
* Copyright (C) 2014 Steven Rostedt, Red Hat Inc
*/
#include <linux/linkage.h>
#include <asm/ptrace.h>
#include <asm/ftrace.h>
#include <asm/export.h>
#include <asm/nospec-branch.h>
#include <asm/unwind_hints.h>
.code64
.section .entry.text, "ax"
# define function_hook __fentry__
EXPORT_SYMBOL(__fentry__)
#ifdef CONFIG_FRAME_POINTER
/* Save parent and function stack frames (rip and rbp) */
# define MCOUNT_FRAME_SIZE (8+16*2)
#else
/* No need to save a stack frame */
# define MCOUNT_FRAME_SIZE 0
#endif /* CONFIG_FRAME_POINTER */
/* Size of stack used to save mcount regs in save_mcount_regs */
#define MCOUNT_REG_SIZE (SS+8 + MCOUNT_FRAME_SIZE)
/*
* gcc -pg option adds a call to 'mcount' in most functions.
* When -mfentry is used, the call is to 'fentry' and not 'mcount'
* and is done before the function's stack frame is set up.
* They both require a set of regs to be saved before calling
* any C code and restored before returning back to the function.
*
* On boot up, all these calls are converted into nops. When tracing
* is enabled, the call can jump to either ftrace_caller or
* ftrace_regs_caller. Callbacks (tracing functions) that require
* ftrace_regs_caller (like kprobes) need to have pt_regs passed to
* it. For this reason, the size of the pt_regs structure will be
* allocated on the stack and the required mcount registers will
* be saved in the locations that pt_regs has them in.
*/
/*
* @added: the amount of stack added before calling this
*
* After this is called, the following registers contain:
*
* %rdi - holds the address that called the trampoline
* %rsi - holds the parent function (traced function's return address)
* %rdx - holds the original %rbp
*/
.macro save_mcount_regs added=0
#ifdef CONFIG_FRAME_POINTER
/* Save the original rbp */
pushq %rbp
/*
* Stack traces will stop at the ftrace trampoline if the frame pointer
* is not set up properly. If fentry is used, we need to save a frame
* pointer for the parent as well as the function traced, because the
* fentry is called before the stack frame is set up, where as mcount
* is called afterward.
*/
/* Save the parent pointer (skip orig rbp and our return address) */
pushq \added+8*2(%rsp)
pushq %rbp
movq %rsp, %rbp
/* Save the return address (now skip orig rbp, rbp and parent) */
pushq \added+8*3(%rsp)
pushq %rbp
movq %rsp, %rbp
#endif /* CONFIG_FRAME_POINTER */
/*
* We add enough stack to save all regs.
*/
subq $(MCOUNT_REG_SIZE - MCOUNT_FRAME_SIZE), %rsp
movq %rax, RAX(%rsp)
movq %rcx, RCX(%rsp)
movq %rdx, RDX(%rsp)
movq %rsi, RSI(%rsp)
movq %rdi, RDI(%rsp)
movq %r8, R8(%rsp)
movq %r9, R9(%rsp)
/*
* Save the original RBP. Even though the mcount ABI does not
* require this, it helps out callers.
*/
#ifdef CONFIG_FRAME_POINTER
movq MCOUNT_REG_SIZE-8(%rsp), %rdx
#else
movq %rbp, %rdx
#endif
movq %rdx, RBP(%rsp)
/* Copy the parent address into %rsi (second parameter) */
movq MCOUNT_REG_SIZE+8+\added(%rsp), %rsi
/* Move RIP to its proper location */
movq MCOUNT_REG_SIZE+\added(%rsp), %rdi
movq %rdi, RIP(%rsp)
/*
* Now %rdi (the first parameter) has the return address of
* where ftrace_call returns. But the callbacks expect the
* address of the call itself.
*/
subq $MCOUNT_INSN_SIZE, %rdi
.endm
.macro restore_mcount_regs
movq R9(%rsp), %r9
movq R8(%rsp), %r8
movq RDI(%rsp), %rdi
movq RSI(%rsp), %rsi
movq RDX(%rsp), %rdx
movq RCX(%rsp), %rcx
movq RAX(%rsp), %rax
/* ftrace_regs_caller can modify %rbp */
movq RBP(%rsp), %rbp
addq $MCOUNT_REG_SIZE, %rsp
.endm
#ifdef CONFIG_DYNAMIC_FTRACE
ENTRY(function_hook)
retq
ENDPROC(function_hook)
ENTRY(ftrace_caller)
/* save_mcount_regs fills in first two parameters */
save_mcount_regs
GLOBAL(ftrace_caller_op_ptr)
/* Load the ftrace_ops into the 3rd parameter */
movq function_trace_op(%rip), %rdx
/* regs go into 4th parameter (but make it NULL) */
movq $0, %rcx
GLOBAL(ftrace_call)
call ftrace_stub
restore_mcount_regs
/*
* The code up to this label is copied into trampolines so
* think twice before adding any new code or changing the
* layout here.
*/
GLOBAL(ftrace_epilogue)
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
GLOBAL(ftrace_graph_call)
jmp ftrace_stub
#endif
/*
* This is weak to keep gas from relaxing the jumps.
* It is also used to copy the retq for trampolines.
*/
WEAK(ftrace_stub)
retq
ENDPROC(ftrace_caller)
ENTRY(ftrace_regs_caller)
/* Save the current flags before any operations that can change them */
pushfq
/* added 8 bytes to save flags */
save_mcount_regs 8
/* save_mcount_regs fills in first two parameters */
GLOBAL(ftrace_regs_caller_op_ptr)
/* Load the ftrace_ops into the 3rd parameter */
movq function_trace_op(%rip), %rdx
/* Save the rest of pt_regs */
movq %r15, R15(%rsp)
movq %r14, R14(%rsp)
movq %r13, R13(%rsp)
movq %r12, R12(%rsp)
movq %r11, R11(%rsp)
movq %r10, R10(%rsp)
movq %rbx, RBX(%rsp)
/* Copy saved flags */
movq MCOUNT_REG_SIZE(%rsp), %rcx
movq %rcx, EFLAGS(%rsp)
/* Kernel segments */
movq $__KERNEL_DS, %rcx
movq %rcx, SS(%rsp)
movq $__KERNEL_CS, %rcx
movq %rcx, CS(%rsp)
/* Stack - skipping return address and flags */
leaq MCOUNT_REG_SIZE+8*2(%rsp), %rcx
movq %rcx, RSP(%rsp)
/* regs go into 4th parameter */
leaq (%rsp), %rcx
GLOBAL(ftrace_regs_call)
call ftrace_stub
/* Copy flags back to SS, to restore them */
movq EFLAGS(%rsp), %rax
movq %rax, MCOUNT_REG_SIZE(%rsp)
/* Handlers can change the RIP */
movq RIP(%rsp), %rax
movq %rax, MCOUNT_REG_SIZE+8(%rsp)
/* restore the rest of pt_regs */
movq R15(%rsp), %r15
movq R14(%rsp), %r14
movq R13(%rsp), %r13
movq R12(%rsp), %r12
movq R10(%rsp), %r10
movq RBX(%rsp), %rbx
restore_mcount_regs
/* Restore flags */
popfq
/*
* As this jmp to ftrace_epilogue can be a short jump
* it must not be copied into the trampoline.
* The trampoline will add the code to jump
* to the return.
*/
GLOBAL(ftrace_regs_caller_end)
jmp ftrace_epilogue
ENDPROC(ftrace_regs_caller)
#else /* ! CONFIG_DYNAMIC_FTRACE */
ENTRY(function_hook)
cmpq $ftrace_stub, ftrace_trace_function
jnz trace
fgraph_trace:
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
cmpq $ftrace_stub, ftrace_graph_return
jnz ftrace_graph_caller
cmpq $ftrace_graph_entry_stub, ftrace_graph_entry
jnz ftrace_graph_caller
#endif
GLOBAL(ftrace_stub)
retq
trace:
/* save_mcount_regs fills in first two parameters */
save_mcount_regs
/*
* When DYNAMIC_FTRACE is not defined, ARCH_SUPPORTS_FTRACE_OPS is not
* set (see include/asm/ftrace.h and include/linux/ftrace.h). Only the
* ip and parent ip are used and the list function is called when
* function tracing is enabled.
*/
movq ftrace_trace_function, %r8
CALL_NOSPEC %r8
restore_mcount_regs
jmp fgraph_trace
ENDPROC(function_hook)
#endif /* CONFIG_DYNAMIC_FTRACE */
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
ENTRY(ftrace_graph_caller)
/* Saves rbp into %rdx and fills first parameter */
save_mcount_regs
leaq MCOUNT_REG_SIZE+8(%rsp), %rsi
movq $0, %rdx /* No framepointers needed */
call prepare_ftrace_return
restore_mcount_regs
retq
ENDPROC(ftrace_graph_caller)
ENTRY(return_to_handler)
UNWIND_HINT_EMPTY
subq $24, %rsp
/* Save the return values */
movq %rax, (%rsp)
movq %rdx, 8(%rsp)
movq %rbp, %rdi
call ftrace_return_to_handler
movq %rax, %rdi
movq 8(%rsp), %rdx
movq (%rsp), %rax
addq $24, %rsp
JMP_NOSPEC %rdi
END(return_to_handler)
#endif