Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752186AbdCDNDK (ORCPT ); Sat, 4 Mar 2017 08:03:10 -0500 Received: from mail-lf0-f68.google.com ([209.85.215.68]:34580 "EHLO mail-lf0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752049AbdCDNDI (ORCPT ); Sat, 4 Mar 2017 08:03:08 -0500 Date: Sat, 4 Mar 2017 14:02:17 +0100 From: Rabin Vincent To: Abel Vesa Cc: 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: <20170304130216.uz6chruwmyb2u4yv@debian> References: <1488588672-21865-1-git-send-email-abelvesa@linux.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1488588672-21865-1-git-send-email-abelvesa@linux.com> User-Agent: NeoMutt/20161126 (1.7.1) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5406 Lines: 163 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.