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linux_dsm_epyc7002/arch/arm/kernel/entry-ftrace.S
Abel Vesa 620176f335 ARM: 8678/1: ftrace: Adds support for CONFIG_DYNAMIC_FTRACE_WITH_REGS 
The DYNAMIC_FTRACE_WITH_REGS configuration makes it possible for a
ftrace operation to specify if registers need to saved/restored by
the ftrace handler. This is needed by kgraft and possibly other
ftrace-based tools, and the ARM architecture is currently lacking
this feature. It would also be the first step to support the
"Kprobes-on-ftrace" optimization on ARM.

This patch introduces a new ftrace handler that stores the registers
on the stack before calling the next stage. The registers are restored
from the stack before going back to the instrumented function.

A side-effect of this patch is to activate the support for
ftrace_modify_call() as it defines ARCH_SUPPORTS_FTRACE_OPS for the
ARM architecture.

Signed-off-by: Abel Vesa <abelvesa@linux.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
2017-06-18 22:25:16 +01:00

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/*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*/
#include <asm/assembler.h>
#include <asm/ftrace.h>
#include <asm/unwind.h>
#include "entry-header.S"
/*
* When compiling with -pg, gcc inserts a call to the mcount routine at the
* start of every function. In mcount, apart from the function's address (in
* lr), we need to get hold of the function's caller's address.
*
* Older GCCs (pre-4.4) inserted a call to a routine called mcount like this:
*
* bl mcount
*
* These versions have the limitation that in order for the mcount routine to
* be able to determine the function's caller's address, an APCS-style frame
* pointer (which is set up with something like the code below) is required.
*
* mov ip, sp
* push {fp, ip, lr, pc}
* sub fp, ip, #4
*
* With EABI, these frame pointers are not available unless -mapcs-frame is
* specified, and if building as Thumb-2, not even then.
*
* Newer GCCs (4.4+) solve this problem by introducing a new version of mcount,
* with call sites like:
*
* push {lr}
* bl __gnu_mcount_nc
*
* With these compilers, frame pointers are not necessary.
*
* mcount can be thought of as a function called in the middle of a subroutine
* call. As such, it needs to be transparent for both the caller and the
* callee: the original lr needs to be restored when leaving mcount, and no
* registers should be clobbered. (In the __gnu_mcount_nc implementation, we
* clobber the ip register. This is OK because the ARM calling convention
* allows it to be clobbered in subroutines and doesn't use it to hold
* parameters.)
*
* When using dynamic ftrace, we patch out the mcount call by a "mov r0, r0"
* for the mcount case, and a "pop {lr}" for the __gnu_mcount_nc case (see
* arch/arm/kernel/ftrace.c).
*/
#ifndef CONFIG_OLD_MCOUNT
#if (__GNUC__ < 4 || (__GNUC__ == 4 && __GNUC_MINOR__ < 4))
#error Ftrace requires CONFIG_FRAME_POINTER=y with GCC older than 4.4.0.
#endif
#endif
.macro mcount_adjust_addr rd, rn
bic \rd, \rn, #1 @ clear the Thumb bit if present
sub \rd, \rd, #MCOUNT_INSN_SIZE
.endm
.macro __mcount suffix
mcount_enter
ldr r0, =ftrace_trace_function
ldr r2, [r0]
adr r0, .Lftrace_stub
cmp r0, r2
bne 1f
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
ldr r1, =ftrace_graph_return
ldr r2, [r1]
cmp r0, r2
bne ftrace_graph_caller\suffix
ldr r1, =ftrace_graph_entry
ldr r2, [r1]
ldr r0, =ftrace_graph_entry_stub
cmp r0, r2
bne ftrace_graph_caller\suffix
#endif
mcount_exit
1: mcount_get_lr r1 @ lr of instrumented func
mcount_adjust_addr r0, lr @ instrumented function
badr lr, 2f
mov pc, r2
2: mcount_exit
.endm
#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
.macro __ftrace_regs_caller
sub sp, sp, #8 @ space for PC and CPSR OLD_R0,
@ OLD_R0 will overwrite previous LR
add ip, sp, #12 @ move in IP the value of SP as it was
@ before the push {lr} of the mcount mechanism
str lr, [sp, #0] @ store LR instead of PC
ldr lr, [sp, #8] @ get previous LR
str r0, [sp, #8] @ write r0 as OLD_R0 over previous LR
stmdb sp!, {ip, lr}
stmdb sp!, {r0-r11, lr}
@ stack content at this point:
@ 0 4 48 52 56 60 64 68 72
@ R0 | R1 | ... | LR | SP + 4 | previous LR | LR | PSR | OLD_R0 |
mov r3, sp @ struct pt_regs*
ldr r2, =function_trace_op
ldr r2, [r2] @ pointer to the current
@ function tracing op
ldr r1, [sp, #S_LR] @ lr of instrumented func
ldr lr, [sp, #S_PC] @ get LR
mcount_adjust_addr r0, lr @ instrumented function
.globl ftrace_regs_call
ftrace_regs_call:
bl ftrace_stub
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
.globl ftrace_graph_regs_call
ftrace_graph_regs_call:
mov r0, r0
#endif
@ pop saved regs
ldmia sp!, {r0-r12} @ restore r0 through r12
ldr ip, [sp, #8] @ restore PC
ldr lr, [sp, #4] @ restore LR
ldr sp, [sp, #0] @ restore SP
mov pc, ip @ return
.endm
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
.macro __ftrace_graph_regs_caller
sub r0, fp, #4 @ lr of instrumented routine (parent)
@ called from __ftrace_regs_caller
ldr r1, [sp, #S_PC] @ instrumented routine (func)
mcount_adjust_addr r1, r1
mov r2, fp @ frame pointer
bl prepare_ftrace_return
@ pop registers saved in ftrace_regs_caller
ldmia sp!, {r0-r12} @ restore r0 through r12
ldr ip, [sp, #8] @ restore PC
ldr lr, [sp, #4] @ restore LR
ldr sp, [sp, #0] @ restore SP
mov pc, ip @ return
.endm
#endif
#endif
.macro __ftrace_caller suffix
mcount_enter
mcount_get_lr r1 @ lr of instrumented func
mcount_adjust_addr r0, lr @ instrumented function
#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
ldr r2, =function_trace_op
ldr r2, [r2] @ pointer to the current
@ function tracing op
mov r3, #0 @ regs is NULL
#endif
.globl ftrace_call\suffix
ftrace_call\suffix:
bl ftrace_stub
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
.globl ftrace_graph_call\suffix
ftrace_graph_call\suffix:
mov r0, r0
#endif
mcount_exit
.endm
.macro __ftrace_graph_caller
sub r0, fp, #4 @ &lr of instrumented routine (&parent)
#ifdef CONFIG_DYNAMIC_FTRACE
@ called from __ftrace_caller, saved in mcount_enter
ldr r1, [sp, #16] @ instrumented routine (func)
mcount_adjust_addr r1, r1
#else
@ called from __mcount, untouched in lr
mcount_adjust_addr r1, lr @ instrumented routine (func)
#endif
mov r2, fp @ frame pointer
bl prepare_ftrace_return
mcount_exit
.endm
#ifdef CONFIG_OLD_MCOUNT
/*
* mcount
*/
.macro mcount_enter
stmdb sp!, {r0-r3, lr}
.endm
.macro mcount_get_lr reg
ldr \reg, [fp, #-4]
.endm
.macro mcount_exit
ldr lr, [fp, #-4]
ldmia sp!, {r0-r3, pc}
.endm
ENTRY(mcount)
#ifdef CONFIG_DYNAMIC_FTRACE
stmdb sp!, {lr}
ldr lr, [fp, #-4]
ldmia sp!, {pc}
#else
__mcount _old
#endif
ENDPROC(mcount)
#ifdef CONFIG_DYNAMIC_FTRACE
ENTRY(ftrace_caller_old)
__ftrace_caller _old
ENDPROC(ftrace_caller_old)
#endif
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
ENTRY(ftrace_graph_caller_old)
__ftrace_graph_caller
ENDPROC(ftrace_graph_caller_old)
#endif
.purgem mcount_enter
.purgem mcount_get_lr
.purgem mcount_exit
#endif
/*
* __gnu_mcount_nc
*/
.macro mcount_enter
/*
* This pad compensates for the push {lr} at the call site. Note that we are
* unable to unwind through a function which does not otherwise save its lr.
*/
UNWIND(.pad #4)
stmdb sp!, {r0-r3, lr}
UNWIND(.save {r0-r3, lr})
.endm
.macro mcount_get_lr reg
ldr \reg, [sp, #20]
.endm
.macro mcount_exit
ldmia sp!, {r0-r3, ip, lr}
ret ip
.endm
ENTRY(__gnu_mcount_nc)
UNWIND(.fnstart)
#ifdef CONFIG_DYNAMIC_FTRACE
mov ip, lr
ldmia sp!, {lr}
ret ip
#else
__mcount
#endif
UNWIND(.fnend)
ENDPROC(__gnu_mcount_nc)
#ifdef CONFIG_DYNAMIC_FTRACE
ENTRY(ftrace_caller)
UNWIND(.fnstart)
__ftrace_caller
UNWIND(.fnend)
ENDPROC(ftrace_caller)
#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
ENTRY(ftrace_regs_caller)
UNWIND(.fnstart)
__ftrace_regs_caller
UNWIND(.fnend)
ENDPROC(ftrace_regs_caller)
#endif
#endif
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
ENTRY(ftrace_graph_caller)
UNWIND(.fnstart)
__ftrace_graph_caller
UNWIND(.fnend)
ENDPROC(ftrace_graph_caller)
#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
ENTRY(ftrace_graph_regs_caller)
UNWIND(.fnstart)
__ftrace_graph_regs_caller
UNWIND(.fnend)
ENDPROC(ftrace_graph_regs_caller)
#endif
#endif
.purgem mcount_enter
.purgem mcount_get_lr
.purgem mcount_exit
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
.globl return_to_handler
return_to_handler:
stmdb sp!, {r0-r3}
mov r0, fp @ frame pointer
bl ftrace_return_to_handler
mov lr, r0 @ r0 has real ret addr
ldmia sp!, {r0-r3}
ret lr
#endif
ENTRY(ftrace_stub)
.Lftrace_stub:
ret lr
ENDPROC(ftrace_stub)
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