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

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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: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
This commit is contained in:
Ard Biesheuvel 2022-01-25 15:55:24 +01:00
parent 538b9265c0
commit 41918ec82e
6 changed files with 40 additions and 34 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

2
arch/arm/Kconfig
View file

@ -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

2
arch/arm/Kconfig.debug
View file

@ -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

18
arch/arm/include/asm/ftrace.h
View file

@ -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

5
arch/arm/kernel/Makefile
View file

@ -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

24
arch/arm/kernel/entry-ftrace.S
View file

@ -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)

19
arch/arm/kernel/ftrace.c
View file

@ -22,6 +22,7 @@
#include <asm/ftrace.h>
#include <asm/insn.h>
#include <asm/set_memory.h>
#include <asm/stacktrace.h>
#include <asm/patch.h>
/*
@ -224,8 +225,10 @@ int ftrace_make_nop(struct module *mod,
#endif /* CONFIG_DYNAMIC_FTRACE */
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
asmlinkage
void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
unsigned long frame_pointer)
unsigned long frame_pointer,
unsigned long stack_pointer)
{
unsigned long return_hooker = (unsigned long) &return_to_handler;
unsigned long old;
@ -236,6 +239,18 @@ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
if (IS_ENABLED(CONFIG_UNWINDER_FRAME_POINTER)) {
/* FP points one word below parent's top of stack */
frame_pointer += 4;
} else {
struct stackframe frame = {
.fp = frame_pointer,
.sp = stack_pointer,
.lr = self_addr,
.pc = self_addr,
};
if (unwind_frame(&frame) < 0)
return;
if (frame.lr != self_addr)
parent = frame.lr_addr;
frame_pointer = frame.sp;
}
old = *parent;
@ -258,7 +273,7 @@ static int __ftrace_modify_caller(unsigned long *callsite,
unsigned long caller_fn = (unsigned long) func;
unsigned long pc = (unsigned long) callsite;
unsigned long branch = arm_gen_branch(pc, caller_fn);
unsigned long nop = 0xe1a00000; /* mov r0, r0 */
unsigned long nop = arm_gen_nop();
unsigned long old = enable ? nop : branch;
unsigned long new = enable ? branch : nop;