Messages in this thread | | | From | Jean-Jacques Hiblot <> | Date | Fri, 10 Feb 2017 10:54:57 +0100 | Subject | Re: [PATCHv2] arm: ftrace: Adds support for CONFIG_DYNAMIC_FTRACE_WITH_REGS |
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2017-02-07 20:18 GMT+01:00 Abel Vesa <abelvesa@gmail.com>: > On Wed, Jan 25, 2017 at 07:30:32PM +0100, Jean-Jacques Hiblot wrote: > >> Abel, I tested it partially. > > OK, so I managed to find exactly what is happening. > >> It's seems OK if I have FRAME_POINTER enabled and it breaks otherwise. > > FRAME_POINTER is needed by OLD_MCOUNT. > > OLD_MCOUNT is needed by __ftrace_modify_code in order to be able to do set_kernel_text_rw. > (The other implementation does not allow writing to kernel text therefore the warning > happens)
That seems strange. It shouldn't make a difference whether the old_mcount is enabled or not, we need to be able to modify the code. IMO the ARM implementation of __ftrace_modify_code() and arch_ftrace_update_code() must not be excluded when CONFIG_OLD_MCOUNT is not defined.
> > If you try the same thing without the patch you will get an "Invalid argument" at > module loading. > >> >> My test case attaches a tracing handler to a function "myfunc": >> >> static struct ftrace_ops kprobe_ftrace_ops __read_mostly = { >> .func = jjh_ftrace_handler, >> .flags = FTRACE_OPS_FL_SAVE_REGS | FTRACE_OPS_FL_DYNAMIC, >> }; >> >> ftrace_set_filter(&kprobe_ftrace_ops, "myfunc", 4, 0); >> register_ftrace_function(&kprobe_ftrace_ops); >> >> I won't send the actual code because it's too messy. If you need help >> to reproduce, I'll try to extract the relevant part. >> >> Before the crash I observe the following warning. >> ------------[ cut here ]------------ >> WARNING: CPU: 0 PID: 9 at kernel/trace/ftrace.c:2526 >> ftrace_modify_all_code+0xd8/0x158 >> Modules linked in: jjh_test(+) >> CPU: 0 PID: 9 Comm: migration/0 Tainted: G W 4.7.0+ #53 >> Hardware name: ARM-Versatile Express >> [<8010f7bc>] (unwind_backtrace) from [<8010b6f8>] (show_stack+0x18/0x1c) >> [<8010b6f8>] (show_stack) from [<803a1548>] (dump_stack+0x80/0xa0) >> [<803a1548>] (dump_stack) from [<8011ef20>] (__warn+0xe0/0x10c) >> [<8011ef20>] (__warn) from [<8011ef74>] (warn_slowpath_null+0x28/0x30) >> [<8011ef74>] (warn_slowpath_null) from [<8019d2a4>] >> (ftrace_modify_all_code+0xd8/0x158) >> [<8019d2a4>] (ftrace_modify_all_code) from [<8019d330>] >> (__ftrace_modify_code+0xc/0x14) >> [<8019d330>] (__ftrace_modify_code) from [<80198908>] >> (multi_cpu_stop+0xe8/0x114) >> [<80198908>] (multi_cpu_stop) from [<80198588>] (cpu_stopper_thread+0x60/0x134) >> [<80198588>] (cpu_stopper_thread) from [<8013f428>] >> (smpboot_thread_fn+0x148/0x1c4) >> [<8013f428>] (smpboot_thread_fn) from [<8013c00c>] (kthread+0xe0/0xfc) >> [<8013c00c>] (kthread) from [<80107db8>] (ret_from_fork+0x14/0x3c) >> ---[ end trace f7d50cc2a4627fb1 ]--- >> >> Jean-Jacques >> >> >> >> >> 2017-01-25 0:24 GMT+01:00 Abel Vesa <abelvesa@linux.com>: >> > 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 | 79 ++++++++++++++++++++++++++++++++++++++++++ >> > arch/arm/kernel/ftrace.c | 33 ++++++++++++++++++ >> > 4 files changed, 117 insertions(+) >> > >> > diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig >> > index 186c4c2..db40973 100644 >> > --- a/arch/arm/Kconfig >> > +++ b/arch/arm/Kconfig >> > @@ -50,6 +50,7 @@ config ARM >> > select HAVE_DMA_API_DEBUG >> > select HAVE_DMA_CONTIGUOUS if MMU >> > select HAVE_DYNAMIC_FTRACE if (!XIP_KERNEL) && !CPU_ENDIAN_BE32 && MMU > > The solution is to replace this: >> > + select HAVE_DYNAMIC_FTRACE_WITH_REGS if HAVE_DYNAMIC_FTRACE > with this: > + 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..fcdcc3a 100644 >> > --- a/arch/arm/kernel/entry-ftrace.S >> > +++ b/arch/arm/kernel/entry-ftrace.S >> > @@ -92,12 +92,74 @@ >> > 2: mcount_exit >> > .endm >> > >> > +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS >> > + >> > +.macro __ftrace_regs_caller >> > + >> > + add ip, sp, #4 @ 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 44 48 52 56 60 64 >> > + @ RO | R1 | ... | R11 | LR | SP + 4 | LR | PC | 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, #64] @ 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 >> > + ldr lr, [sp, #64] @ get the previous LR value from stack >> > + ldmia sp, {r0-r11, ip, sp} @ pop the saved registers INCLUDING >> > + @ the stack pointer >> > + ret ip >> > +.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, #56] @ instrumented routine (func) >> > + mcount_adjust_addr r1, r1 >> > + >> > + sub r2, r0, #4 @ frame pointer >> > + bl prepare_ftrace_return >> > + >> > + ldr lr, [sp, #64] @ restore lr from the stack >> > + ldmia sp, {r0-r11, ip, sp} @ restore r0 through sp >> > + ret ip >> > + >> > +.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 +274,15 @@ 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 +291,14 @@ 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..d8d4753 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; >> > @@ -157,6 +166,20 @@ 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); >> > +} >> > + > > Also this function implementation needs to be in an #ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS clause: > >> > +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); >> > @@ -229,6 +252,8 @@ 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 +276,14 @@ 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 >> > > > I tested it and it works now. An update version of this patch will follow. > (It also include all fixes for all the other comments on this thread) > > Thanks, > Abel
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