[PATCHv4] arm: ftrace: Adds support for CONFIG_DYNAMIC_FTRACE_WITH_REGS

Abel Vesa
2017-02-24T22:58:20Z

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>
---
arch/arm/Kconfig | 1 +
arch/arm/include/asm/ftrace.h | 4 ++
arch/arm/kernel/entry-ftrace.S | 83 ++++++++++++++++++++++++++++++++++++++++++
arch/arm/kernel/ftrace.c | 37 +++++++++++++++++++
4 files changed, 125 insertions(+)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index fda6a46..877df5b 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -55,6 +55,7 @@ config ARM
select HAVE_DMA_API_DEBUG
select HAVE_DMA_CONTIGUOUS if MMU
select HAVE_DYNAMIC_FTRACE if (!XIP_KERNEL) && !CPU_ENDIAN_BE32 && MMU
+ select HAVE_DYNAMIC_FTRACE_WITH_REGS if HAVE_DYNAMIC_FTRACE && OLD_MCOUNT
select HAVE_EFFICIENT_UNALIGNED_ACCESS if (CPU_V6 || CPU_V6K || CPU_V7) && MMU
select HAVE_EXIT_THREAD
select HAVE_FTRACE_MCOUNT_RECORD if (!XIP_KERNEL)
diff --git a/arch/arm/include/asm/ftrace.h b/arch/arm/include/asm/ftrace.h
index 22b7311..f379881 100644
--- a/arch/arm/include/asm/ftrace.h
+++ b/arch/arm/include/asm/ftrace.h
@@ -1,6 +1,10 @@
#ifndef _ASM_ARM_FTRACE
#define _ASM_ARM_FTRACE

+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
+#define ARCH_SUPPORTS_FTRACE_OPS 1
+#endif
+
#ifdef CONFIG_FUNCTION_TRACER
#define MCOUNT_ADDR ((unsigned long)(__gnu_mcount_nc))
#define MCOUNT_INSN_SIZE 4 /* sizeof mcount call */
diff --git a/arch/arm/kernel/entry-ftrace.S b/arch/arm/kernel/entry-ftrace.S
index c73c403..3916dd6 100644
--- a/arch/arm/kernel/entry-ftrace.S
+++ b/arch/arm/kernel/entry-ftrace.S
@@ -92,12 +92,78 @@
2: mcount_exit
.endm

+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
+
+.macro __ftrace_regs_caller
+
+ sub sp, sp, #8 @ space for CPSR and OLD_R0 (not used)
+
+ add ip, sp, #12 @ move in IP the value of SP as it was
+ @ before the push {lr} of the mcount mechanism
+ stmdb sp!, {ip,lr,pc}
+ stmdb sp!, {r0-r11,lr}
+
+ @ stack content at this point:
+ @ 0 4 48 52 56 60 64 68 72
+ @ R0 | R1 | ... | LR | SP + 4 | LR | PC | PSR | OLD_R0 | previous LR |
+
+ mov r3, sp @ struct pt_regs*
+ ldr r2, =function_trace_op
+ ldr r2, [r2] @ pointer to the current
+ @ function tracing op
+ ldr r1, [sp, #PT_REGS_SIZE] @ lr of instrumented func
+ 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
+ @ first, get the previous LR value from stack
+ ldr lr, [sp, #PT_REGS_SIZE]
+ @ now pop the rest of the saved registers INCLUDING stack pointer
+ ldmia sp, {r0-r11, ip, sp, pc}
+.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_LR] @ instrumented routine (func)
+ mcount_adjust_addr r1, r1
+
+ sub r2, r0, #4 @ frame pointer
+ bl prepare_ftrace_return
+
+ @ pop registers saved in ftrace_regs_caller
+ @ first, get the previous LR value from stack
+ ldr lr, [sp, #PT_REGS_SIZE]
+ @ now pop the rest of the saved registers INCLUDING stack pointer
+ ldmia sp, {r0-r11, ip, sp, pc}
+.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
@@ -212,6 +278,15 @@ 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
@@ -220,6 +295,14 @@ 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
diff --git a/arch/arm/kernel/ftrace.c b/arch/arm/kernel/ftrace.c
index 3f17594..cb0358c 100644
--- a/arch/arm/kernel/ftrace.c
+++ b/arch/arm/kernel/ftrace.c
@@ -139,6 +139,15 @@ int ftrace_update_ftrace_func(ftrace_func_t func)

ret = ftrace_modify_code(pc, 0, new, false);

+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
+ if (!ret) {
+ pc = (unsigned long)&ftrace_regs_call;
+ new = ftrace_call_replace(pc, (unsigned long)func);
+
+ ret = ftrace_modify_code(pc, 0, new, false);
+ }
+#endif
+
#ifdef CONFIG_OLD_MCOUNT
if (!ret) {
pc = (unsigned long)&ftrace_call_old;
@@ -157,11 +166,29 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
unsigned long ip = rec->ip;

old = ftrace_nop_replace(rec);
+
+ new = ftrace_call_replace(ip, adjust_address(rec, addr));
+
+ return ftrace_modify_code(rec->ip, old, new, true);
+}
+
+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
+
+int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
+ unsigned long addr)
+{
+ unsigned long new, old;
+ unsigned long ip = rec->ip;
+
+ old = ftrace_call_replace(ip, adjust_address(rec, old_addr));
+
new = ftrace_call_replace(ip, adjust_address(rec, addr));

return ftrace_modify_code(rec->ip, old, new, true);
}

+#endif
+
int ftrace_make_nop(struct module *mod,
struct dyn_ftrace *rec, unsigned long addr)
{
@@ -229,6 +256,8 @@ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
extern unsigned long ftrace_graph_call;
extern unsigned long ftrace_graph_call_old;
extern void ftrace_graph_caller_old(void);
+extern unsigned long ftrace_graph_regs_call;
+extern void ftrace_graph_regs_caller(void);

static int __ftrace_modify_caller(unsigned long *callsite,
void (*func) (void), bool enable)
@@ -251,6 +280,14 @@ static int ftrace_modify_graph_caller(bool enable)
ftrace_graph_caller,
enable);

+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
+ if (!ret)
+ ret = __ftrace_modify_caller(&ftrace_graph_regs_call,
+ ftrace_graph_regs_caller,
+ enable);
+#endif
+
+
#ifdef CONFIG_OLD_MCOUNT
if (!ret)
ret = __ftrace_modify_caller(&ftrace_graph_call_old,
--
2.7.4