Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752673AbdCSVJe (ORCPT ); Sun, 19 Mar 2017 17:09:34 -0400 Received: from mail-wr0-f195.google.com ([209.85.128.195]:33192 "EHLO mail-wr0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752547AbdCSVJb (ORCPT ); Sun, 19 Mar 2017 17:09:31 -0400 Date: Sun, 19 Mar 2017 21:09:07 +0000 From: Abel Vesa To: Rabin Vincent Cc: Abel Vesa , robin.murphy@arm.com, jjhiblot@traphandler.com, nicstange@gmail.com, Russell King , Steven Rostedt , Ingo Molnar , pmladek@suse.com, mhiramat@kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCHv5] arm: ftrace: Adds support for CONFIG_DYNAMIC_FTRACE_WITH_REGS Message-ID: <20170319210907.GA11479@nuc> References: <1488588672-21865-1-git-send-email-abelvesa@linux.com> <20170304130216.uz6chruwmyb2u4yv@debian> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170304130216.uz6chruwmyb2u4yv@debian> User-Agent: Mutt/1.5.23.1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6511 Lines: 179 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 ?