Commit 41918ec8 authored by Ard Biesheuvel's avatar Ard Biesheuvel
Browse files

ARM: ftrace: enable the graph tracer with the EABI unwinder 



Enable the function graph tracer in combination with the EABI unwinder,
so that Thumb2 builds or Clang ARM builds can make use of it.

This involves using the unwinder to locate the return address of an
instrumented function on the stack, so that it can be overridden and
made to refer to the ftrace handling routines that need to be called at
function return.

Given that for these builds, it is not guaranteed that the value of the
link register is stored on the stack, fall back to the stack slot that
will be used by the ftrace exit code to restore LR in the instrumented
function's execution context.

Signed-off-by: default avatarArd Biesheuvel <ardb@kernel.org>
Reviewed-by: default avatarSteven Rostedt (Google) <rostedt@goodmis.org>
parent 538b9265

arch/arm/Kconfig

+1 −1
Original line number Diff line number Diff line
@@ -91,7 +91,7 @@ config ARM 
	select HAVE_EXIT_THREAD

	select HAVE_FAST_GUP if ARM_LPAE

	select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL

	select HAVE_FUNCTION_GRAPH_TRACER if !THUMB2_KERNEL && !CC_IS_CLANG

	select HAVE_FUNCTION_GRAPH_TRACER

	select HAVE_FUNCTION_TRACER if !XIP_KERNEL && !(THUMB2_KERNEL && CC_IS_CLANG)

	select HAVE_FUTEX_CMPXCHG if FUTEX

	select HAVE_GCC_PLUGINS

arch/arm/Kconfig.debug

+1 −1
Original line number Diff line number Diff line
@@ -65,7 +65,7 @@ config UNWINDER_FRAME_POINTER 


config UNWINDER_ARM

	bool "ARM EABI stack unwinder"

	depends on AEABI && !FUNCTION_GRAPH_TRACER

	depends on AEABI

	# https://github.com/ClangBuiltLinux/linux/issues/732

	depends on !LD_IS_LLD || LLD_VERSION >= 110000

	select ARM_UNWIND

arch/arm/include/asm/ftrace.h

+0 −18
Original line number Diff line number Diff line
@@ -35,26 +35,8 @@ static inline unsigned long ftrace_call_adjust(unsigned long addr) 


#ifndef __ASSEMBLY__



#if defined(CONFIG_FRAME_POINTER) && !defined(CONFIG_ARM_UNWIND)

/*

 * return_address uses walk_stackframe to do it's work.  If both

 * CONFIG_FRAME_POINTER=y and CONFIG_ARM_UNWIND=y walk_stackframe uses unwind

 * information.  For this to work in the function tracer many functions would

 * have to be marked with __notrace.  So for now just depend on

 * !CONFIG_ARM_UNWIND.

 */



void *return_address(unsigned int);



#else



static inline void *return_address(unsigned int level)

{

	return NULL;

}



#endif



#define ftrace_return_address(n) return_address(n)



#define ARCH_HAS_SYSCALL_MATCH_SYM_NAME

arch/arm/kernel/Makefile

+1 −4
Original line number Diff line number Diff line
@@ -25,10 +25,7 @@ obj-y := elf.o entry-common.o irq.o opcodes.o \ 
KASAN_SANITIZE_stacktrace.o := n

KASAN_SANITIZE_traps.o := n



ifneq ($(CONFIG_ARM_UNWIND),y)

obj-$(CONFIG_FRAME_POINTER)	+= return_address.o

endif



obj-y				+= return_address.o

obj-$(CONFIG_ATAGS)		+= atags_parse.o

obj-$(CONFIG_ATAGS_PROC)	+= atags_proc.o

obj-$(CONFIG_DEPRECATED_PARAM_STRUCT) += atags_compat.o

arch/arm/kernel/entry-ftrace.S

+20 −8
Original line number Diff line number Diff line
@@ -100,7 +100,8 @@ ftrace_regs_call: 
#ifdef CONFIG_FUNCTION_GRAPH_TRACER

	.globl ftrace_graph_regs_call

ftrace_graph_regs_call:

	mov	r0, r0

ARM(	mov	r0, r0	)

THUMB(	nop.w		)

#endif



	@ pop saved regs
@@ -112,13 +113,18 @@ ftrace_graph_regs_call: 
#ifdef CONFIG_FUNCTION_GRAPH_TRACER

.macro __ftrace_graph_regs_caller



#ifdef CONFIG_UNWINDER_FRAME_POINTER

	sub	r0, fp, #4		@ lr of instrumented routine (parent)

#else

	add	r0, sp, #S_LR

#endif



	@ called from __ftrace_regs_caller

	ldr	r1, [sp, #S_PC]		@ instrumented routine (func)

	mcount_adjust_addr	r1, r1



	mov	r2, fp			@ frame pointer

	mov	r2, fpreg		@ frame pointer

	add	r3, sp, #PT_REGS_SIZE

	bl	prepare_ftrace_return



	@ pop registers saved in ftrace_regs_caller
@@ -149,14 +155,19 @@ ftrace_call\suffix: 
#ifdef CONFIG_FUNCTION_GRAPH_TRACER

	.globl ftrace_graph_call\suffix

ftrace_graph_call\suffix:

	mov	r0, r0

ARM(	mov	r0, r0	)

THUMB(	nop.w		)

#endif



	mcount_exit

.endm



.macro __ftrace_graph_caller

#ifdef CONFIG_UNWINDER_FRAME_POINTER

	sub	r0, fp, #4		@ &lr of instrumented routine (&parent)

#else

	add	r0, sp, #20

#endif

#ifdef CONFIG_DYNAMIC_FTRACE

	@ called from __ftrace_caller, saved in mcount_enter

	ldr	r1, [sp, #16]		@ instrumented routine (func)
@@ -165,7 +176,8 @@ ftrace_graph_call\suffix: 
	@ called from __mcount, untouched in lr

	mcount_adjust_addr	r1, lr	@ instrumented routine (func)

#endif

	mov	r2, fp			@ frame pointer

	mov	r2, fpreg		@ frame pointer

	add	r3, sp, #24

	bl	prepare_ftrace_return

	mcount_exit

.endm
@@ -244,14 +256,14 @@ ENDPROC(ftrace_graph_regs_caller) 
.purgem mcount_exit



#ifdef CONFIG_FUNCTION_GRAPH_TRACER

	.globl return_to_handler

return_to_handler:

ENTRY(return_to_handler)

	stmdb	sp!, {r0-r3}

	add	r0, sp, #16		@ sp at exit of instrumented routine

	bl	ftrace_return_to_handler

	mov	lr, r0			@ r0 has real ret addr

	ldmia	sp!, {r0-r3}

	ret	lr

ENDPROC(return_to_handler)

#endif



ENTRY(ftrace_stub)