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 <[email protected]>
---
arch/arm/Kconfig | 1 +
arch/arm/include/asm/ftrace.h | 4 ++
arch/arm/kernel/entry-ftrace.S | 83 ++++++++++++++++++++++++++++++++++++++++++
arch/arm/kernel/ftrace.c | 48 +++++++++++++++++++++---
4 files changed, 131 insertions(+), 5 deletions(-)
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 0d4e71b..bf5d8fa 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -56,6 +56,7 @@ 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
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..93f9abb 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}
+
+ ldr r0, [sp, #S_LR] @ replace PC with LR
+ str r0, [sp, #S_PC] @ into pt_regs
+
+ ldr r1, [sp, #PT_REGS_SIZE] @ replace new LR with
+ str r1, [sp, #S_LR] @ previous LR into pt_regs
+
+ @ 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 | 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
+ ldmia sp, {r0-r15}
+.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-r15}
+.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..f165265 100644
--- a/arch/arm/kernel/ftrace.c
+++ b/arch/arm/kernel/ftrace.c
@@ -29,11 +29,6 @@
#endif
#ifdef CONFIG_DYNAMIC_FTRACE
-#ifdef CONFIG_OLD_MCOUNT
-#define OLD_MCOUNT_ADDR ((unsigned long) mcount)
-#define OLD_FTRACE_ADDR ((unsigned long) ftrace_caller_old)
-
-#define OLD_NOP 0xe1a00000 /* mov r0, r0 */
static int __ftrace_modify_code(void *data)
{
@@ -51,6 +46,12 @@ void arch_ftrace_update_code(int command)
stop_machine(__ftrace_modify_code, &command, NULL);
}
+#ifdef CONFIG_OLD_MCOUNT
+#define OLD_MCOUNT_ADDR ((unsigned long) mcount)
+#define OLD_FTRACE_ADDR ((unsigned long) ftrace_caller_old)
+
+#define OLD_NOP 0xe1a00000 /* mov r0, r0 */
+
static unsigned long ftrace_nop_replace(struct dyn_ftrace *rec)
{
return rec->arch.old_mcount ? OLD_NOP : NOP;
@@ -139,6 +140,15 @@ 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 +167,29 @@ 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 +257,8 @@ 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 +281,14 @@ 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
On Sat, Mar 04, 2017 at 12:51:12AM +0000, Abel Vesa wrote:
> diff --git a/arch/arm/kernel/entry-ftrace.S b/arch/arm/kernel/entry-ftrace.S
> index c73c403..93f9abb 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}
This doesn't build with CONFIG_THUMB2_KERNEL:
entry-ftrace.S:285: Error: PC not allowed in register list -- `stmdb sp!,{ip,lr,pc}'
Saving PC in STMDB is prohibited in Thumb and deprecated in ARM.
> + stmdb sp!, {r0-r11,lr}
> +
> + ldr r0, [sp, #S_LR] @ replace PC with LR
> + str r0, [sp, #S_PC] @ into pt_regs
> +
> + ldr r1, [sp, #PT_REGS_SIZE] @ replace new LR with
> + str r1, [sp, #S_LR] @ previous LR into pt_regs
> +
> + @ 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 | previous LR |
So this code only adjust the SP by 72 bytes. Since the stack is not
aligned to 8 bytes at entry to mcount, this code calls into C functions
with a misaligned stack. This is a violation of the procedure call
standard.
Also, I believe this should have unwind annotations to indicate where it
saved the registers. See mcount_enter for an example.
> +
> + 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
> + ldmia sp, {r0-r15}
This doesn't build either:
entry-ftrace.S:285: Error: LR and PC should not both be in register list -- `ldmia sp,{r0-r15}'
Restoring LR and PC together is prohibited in Thumb and deprecated in
ARM. It's the same case with SP.
> +.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-r15}
This doesn't get built on CONFIG_THUMB2_KERNEL since there's no suppport
for CONFIG_FUNCTION_GRAPH_TRACER there, but this is also using
deprecated operands.
> +.endm
> +#endif
> +#endif
...
> diff --git a/arch/arm/kernel/ftrace.c b/arch/arm/kernel/ftrace.c
> index 3f17594..f165265 100644
> --- a/arch/arm/kernel/ftrace.c
> +++ b/arch/arm/kernel/ftrace.c
> @@ -29,11 +29,6 @@
> #endif
>
> #ifdef CONFIG_DYNAMIC_FTRACE
> -#ifdef CONFIG_OLD_MCOUNT
> -#define OLD_MCOUNT_ADDR ((unsigned long) mcount)
> -#define OLD_FTRACE_ADDR ((unsigned long) ftrace_caller_old)
> -
> -#define OLD_NOP 0xe1a00000 /* mov r0, r0 */
>
> static int __ftrace_modify_code(void *data)
> {
> @@ -51,6 +46,12 @@ void arch_ftrace_update_code(int command)
> stop_machine(__ftrace_modify_code, &command, NULL);
> }
>
> +#ifdef CONFIG_OLD_MCOUNT
> +#define OLD_MCOUNT_ADDR ((unsigned long) mcount)
> +#define OLD_FTRACE_ADDR ((unsigned long) ftrace_caller_old)
> +
> +#define OLD_NOP 0xe1a00000 /* mov r0, r0 */
> +
> static unsigned long ftrace_nop_replace(struct dyn_ftrace *rec)
This chunk above fixes the problem which Nicolai pointed out earlier. Since
it's a bug fix for the current dynamic ftrace code, it should really be
submitted as a separate patch. Feel free to use some variant of this
commit message which I wrote when I ran into this yesterday:
ARM: ftrace: fix dynamic ftrace with DEBUG_RODATA and !FRAME_POINTER
The support for dynamic ftrace with CONFIG_DEBUG_RODATA involves
overriding the weak arch_ftrace_update_code() with a variant which makes
the kernel text writable around the patching.
This override was however added under the CONFIG_OLD_MCOUNT ifdef, and
CONFIG_OLD_MCOUNT is only enabled if frame pointers are enabled.
This leads to non-functional dynamic ftrace (ftrace triggers a
WARN_ON()) when CONFIG_DEBUG_RODATA is enabled and CONFIG_FRAME_POINTER
is not.
Move the override out of that ifdef and into the CONFIG_DYNAMIC_FTRACE
ifdef where it belongs.
Fixes: 80d6b0c2eed2a ("ARM: mm: allow text and rodata sections to be read-only")
> {
> return rec->arch.old_mcount ? OLD_NOP : NOP;
> @@ -139,6 +140,15 @@ int ftrace_update_ftrace_func(ftrace_func_t func)
>
> ret = ftrace_modify_code(pc, 0, new, false);
>
> +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
This code (and the rest of your additions to this file below), are already
under CONFIG_DYNAMIC_FTRACE and afaics CONFIG_DYNAMIC_FTRACE_WITH_REGS is
always enabled when the former is enabled, so could you please drop
these ifdefs?
The code in entry-ftrace.S under CONFIG_DYNAMIC_FTRACE_WITH_REGS would
also benefit from just using CONFIG_DYNAMIC_FTRACE everywhere instead.
On Sat, Mar 04, 2017 at 02:02:17PM +0100, Rabin Vincent wrote:
> On Sat, Mar 04, 2017 at 12:51:12AM +0000, Abel Vesa wrote:
> > diff --git a/arch/arm/kernel/entry-ftrace.S b/arch/arm/kernel/entry-ftrace.S
> > index c73c403..93f9abb 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}
>
> This doesn't build with CONFIG_THUMB2_KERNEL:
>
> entry-ftrace.S:285: Error: PC not allowed in register list -- `stmdb sp!,{ip,lr,pc}'
>
> Saving PC in STMDB is prohibited in Thumb and deprecated in ARM.
>
> > + stmdb sp!, {r0-r11,lr}
> > +
> > + ldr r0, [sp, #S_LR] @ replace PC with LR
> > + str r0, [sp, #S_PC] @ into pt_regs
> > +
> > + ldr r1, [sp, #PT_REGS_SIZE] @ replace new LR with
> > + str r1, [sp, #S_LR] @ previous LR into pt_regs
> > +
> > + @ 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 | previous LR |
>
> So this code only adjust the SP by 72 bytes. Since the stack is not
> aligned to 8 bytes at entry to mcount, this code calls into C functions
> with a misaligned stack. This is a violation of the procedure call
> standard.
>
> Also, I believe this should have unwind annotations to indicate where it
> saved the registers. See mcount_enter for an example.
>
> > +
> > + 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
> > + ldmia sp, {r0-r15}
>
> This doesn't build either:
>
> entry-ftrace.S:285: Error: LR and PC should not both be in register list -- `ldmia sp,{r0-r15}'
>
> Restoring LR and PC together is prohibited in Thumb and deprecated in
> ARM. It's the same case with SP.
>
We could do it in separate instructions, something like:
@ pop saved regs
ldmia sp!, {r0-r12}
ldr ip, [sp, #8]
ldr lr, [sp, #4]
ldr sp, [sp, #0]
mov pc, ip
Same goes for saving the regs, except I need to replace the LR stored outside of ftrace_regs_caller
with OLD_R0 so that the stack would become aligned to 8 bytes.
> > +.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-r15}
>
> This doesn't get built on CONFIG_THUMB2_KERNEL since there's no suppport
> for CONFIG_FUNCTION_GRAPH_TRACER there, but this is also using
> deprecated operands.
>
> > +.endm
> > +#endif
> > +#endif
> ...
> > diff --git a/arch/arm/kernel/ftrace.c b/arch/arm/kernel/ftrace.c
> > index 3f17594..f165265 100644
> > --- a/arch/arm/kernel/ftrace.c
> > +++ b/arch/arm/kernel/ftrace.c
> > @@ -29,11 +29,6 @@
> > #endif
> >
> > #ifdef CONFIG_DYNAMIC_FTRACE
> > -#ifdef CONFIG_OLD_MCOUNT
> > -#define OLD_MCOUNT_ADDR ((unsigned long) mcount)
> > -#define OLD_FTRACE_ADDR ((unsigned long) ftrace_caller_old)
> > -
> > -#define OLD_NOP 0xe1a00000 /* mov r0, r0 */
> >
> > static int __ftrace_modify_code(void *data)
> > {
> > @@ -51,6 +46,12 @@ void arch_ftrace_update_code(int command)
> > stop_machine(__ftrace_modify_code, &command, NULL);
> > }
> >
> > +#ifdef CONFIG_OLD_MCOUNT
> > +#define OLD_MCOUNT_ADDR ((unsigned long) mcount)
> > +#define OLD_FTRACE_ADDR ((unsigned long) ftrace_caller_old)
> > +
> > +#define OLD_NOP 0xe1a00000 /* mov r0, r0 */
> > +
> > static unsigned long ftrace_nop_replace(struct dyn_ftrace *rec)
>
> This chunk above fixes the problem which Nicolai pointed out earlier. Since
> it's a bug fix for the current dynamic ftrace code, it should really be
> submitted as a separate patch. Feel free to use some variant of this
> commit message which I wrote when I ran into this yesterday:
>
> ARM: ftrace: fix dynamic ftrace with DEBUG_RODATA and !FRAME_POINTER
>
> The support for dynamic ftrace with CONFIG_DEBUG_RODATA involves
> overriding the weak arch_ftrace_update_code() with a variant which makes
> the kernel text writable around the patching.
>
> This override was however added under the CONFIG_OLD_MCOUNT ifdef, and
> CONFIG_OLD_MCOUNT is only enabled if frame pointers are enabled.
>
> This leads to non-functional dynamic ftrace (ftrace triggers a
> WARN_ON()) when CONFIG_DEBUG_RODATA is enabled and CONFIG_FRAME_POINTER
> is not.
>
> Move the override out of that ifdef and into the CONFIG_DYNAMIC_FTRACE
> ifdef where it belongs.
>
> Fixes: 80d6b0c2eed2a ("ARM: mm: allow text and rodata sections to be read-only")
>
Sent as a separate patch already.
> > {
> > return rec->arch.old_mcount ? OLD_NOP : NOP;
> > @@ -139,6 +140,15 @@ int ftrace_update_ftrace_func(ftrace_func_t func)
> >
> > ret = ftrace_modify_code(pc, 0, new, false);
> >
> > +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
>
> This code (and the rest of your additions to this file below), are already
> under CONFIG_DYNAMIC_FTRACE and afaics CONFIG_DYNAMIC_FTRACE_WITH_REGS is
> always enabled when the former is enabled, so could you please drop
> these ifdefs?
>
> The code in entry-ftrace.S under CONFIG_DYNAMIC_FTRACE_WITH_REGS would
> also benefit from just using CONFIG_DYNAMIC_FTRACE everywhere instead.
I believe this is incorrect, I think it is worth being compiled in only if
CONFIG_DYNAMIC_FTRACE_WITH_REGS, but this is dependent on CONFIG_DYNAMIC_FTRACE
and the first one is not necessarily enabled if the second one is. Otherwise, what's
the point of having two CONFIGs ?