From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753469AbZJZQLT (ORCPT ); Mon, 26 Oct 2009 12:11:19 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753422AbZJZQLS (ORCPT ); Mon, 26 Oct 2009 12:11:18 -0400 Received: from mail-qy0-f174.google.com ([209.85.221.174]:58318 "EHLO mail-qy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753004AbZJZQLS (ORCPT ); Mon, 26 Oct 2009 12:11:18 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=subject:from:reply-to:to:cc:in-reply-to:references:content-type :organization:date:message-id:mime-version:x-mailer :content-transfer-encoding; b=gWXTlkYHjEyMtj1XAL1bttAlnnYLaR8BkSNRlHYA2qOb84RwUUbcbBWu26Oe3dLP+c qiN38T2kk/nuc67G4hP25Vt11Q+Buy33IPbe7ZvFPDr5090elZFv3tsS+FroLZbAYacr 6rk1y5KI8J+XBFjHfCJvVS2UpbBR7+6xKMnEg= Subject: Re: [PATCH -v5 10/11] tracing: add function graph tracer support for MIPS From: Wu Zhangjin Reply-To: wuzhangjin@gmail.com To: rostedt@goodmis.org Cc: linux-mips@linux-mips.org, linux-kernel@vger.kernel.org, Thomas Gleixner , Ralf Baechle , Nicholas Mc Guire , Richard Sandiford , David Daney , Adam Nemet , Patrik Kluba In-Reply-To: <1256570001.26028.298.camel@gandalf.stny.rr.com> References: <028867b99ec532b84963a35e7d552becc783cafc.1256483735.git.wuzhangjin@gmail.com> <2f73eae542c47ac5bbb9f7280e6c0271d193e90d.1256483735.git.wuzhangjin@gmail.com> <3e0c2d7d8b8f196a8153beb41ea7f3cbf42b3d84.1256483735.git.wuzhangjin@gmail.com> <54c417629e91f40b2bbb4e08cda2a4e6527824c0.1256483735.git.wuzhangjin@gmail.com> <29bccff04932e993ecd9f516d8b6dcf84e2ceecf.1256483735.git.wuzhangjin@gmail.com> <72f2270f7b6e01ca7a4cdf4ac8c21778e5d9652f.1256483735.git.wuzhangjin@gmail.com> <6140dd8f4e1783e5ac30977cf008bb98e4698322.1256483735.git.wuzhangjin@gmail.com> <49b3c441a57f4db423732f81432a3450ccb3240e.1256483735.git.wuzhangjin@gmail.com> <6ad82af0c2ec8ef7b9f536b0a97bf65d385c3945.1256483735.git.wuzhangjin@gmail.com> <1256570001.26028.298.camel@gandalf.stny.rr.com> Content-Type: text/plain Organization: DSLab, Lanzhou University, China Date: Tue, 27 Oct 2009 00:11:07 +0800 Message-Id: <1256573467.5642.214.camel@falcon> Mime-Version: 1.0 X-Mailer: Evolution 2.26.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, On Mon, 2009-10-26 at 11:13 -0400, Steven Rostedt wrote: [...] > > + > > + /* get the code at "ip" */ > > + code = *(unsigned int *)ip; > > Probably want to put the above in an asm with exception handling. > Seems that exception handling in an asm is really "awful"(un-readable) and the above ip is what we have got from the ftrace_graph_caller, it should be okay. but if exception handling is necessary, I will send a new patch for the places(including the following one) which need it. > > + > > + /* If we hit the "move s8(fp), sp" instruction before finding > > + * where the ra is stored, then this is a leaf function and it > > + * does not store the ra on the stack. */ > > + if ((code & MOV_FP_SP) == MOV_FP_SP) > > + return parent_addr; > > + } while (((code & S_RA) != S_RA)); > > Hmm, that condition also looks worrisome. Should we just always search > for s{d,w} R,X(sp)? > > Since there should only be stores of registers into the sp above the > jump to mcount. The break out loop is a check for move. I think it would > be safer to have the break out loop is a check for non storing of a > register into SP. Okay, let's look at this with -mlong-calls, leaf function: ffffffff80243cd8 : ffffffff80243cd8: 67bdfff0 daddiu sp,sp,-16 ffffffff80243cdc: ffbe0008 sd s8,8(sp) ffffffff80243ce0: 03a0f02d move s8,sp ffffffff80243ce4: 3c038021 lui v1,0x8021 ffffffff80243ce8: 646316b0 daddiu v1,v1,5808 ffffffff80243cec: 03e0082d move at,ra ffffffff80243cf0: 0060f809 jalr v1 ffffffff80243cf4: 00020021 nop non-leaf function: ffffffff802414c0 : ffffffff802414c0: 67bdff40 daddiu sp,sp,-192 ffffffff802414c4: ffbe00b0 sd s8,176(sp) ffffffff802414c8: 03a0f02d move s8,sp ffffffff802414cc: ffbf00b8 sd ra,184(sp) ffffffff802414d0: ffb700a8 sd s7,168(sp) ffffffff802414d4: ffb600a0 sd s6,160(sp) ffffffff802414d8: ffb50098 sd s5,152(sp) ffffffff802414dc: ffb40090 sd s4,144(sp) ffffffff802414e0: ffb30088 sd s3,136(sp) ffffffff802414e4: ffb20080 sd s2,128(sp) ffffffff802414e8: ffb10078 sd s1,120(sp) ffffffff802414ec: ffb00070 sd s0,112(sp) ffffffff802414f0: 3c038021 lui v1,0x8021 ffffffff802414f4: 646316b0 daddiu v1,v1,5808 ffffffff802414f8: 03e0082d move at,ra ffffffff802414fc: 0060f809 jalr v1 ffffffff80241500: 00020021 nop ip --> At first, we move to "lui, v1, HI_16BIT_OF_MCOUNT", ip = ip - 12(not 8 when without -mlong-calls, i need to update the source code later). and then, we check whether there is a "Store" instruction, if it's not a "Store" instruction, the function should be a leaf? otherwise, we continue the searching until finding the "s{d,w} ra, offset(sp)" instruction, get the offset, calculate the stack address, and finish? So, we just need to replace this: if ((code & MOV_FP_SP) == MOV_FP_SP) return parent_addr; by #define S_INSN (0xafb0 << 16) if ((code & S_INSN) != S_INSN) return parent_addr; > > > + > > + sp = fp + (code & STACK_OFFSET_MASK); > > + ra = *(unsigned long *)sp; > > Also might want to make the above into a asm with exception handling. > > > + > > + if (ra == parent) > > + return sp; > > + > > + ftrace_graph_stop(); > > + WARN_ON(1); > > + return parent_addr; > > Hmm, may need to do more than this. See below. > > > +} > > + > > +/* > > + * Hook the return address and push it in the stack of return addrs > > + * in current thread info. > > + */ > > +void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr, > > + unsigned long fp) > > +{ > > + unsigned long old; > > + struct ftrace_graph_ent trace; > > + unsigned long return_hooker = (unsigned long) > > + &return_to_handler; > > + > > + if (unlikely(atomic_read(¤t->tracing_graph_pause))) > > + return; > > + > > + /* "parent" is the stack address saved the return address of the caller > > + * of _mcount, for a leaf function not save the return address in the > > + * stack address, so, we "emulate" one in _mcount's stack space, and > > + * hijack it directly, but for a non-leaf function, it will save the > > + * return address to the its stack space, so, we can not hijack the > > + * "parent" directly, but need to find the real stack address, > > + * ftrace_get_parent_addr() does it! > > + */ > > + > > + old = *parent; > > + > > + parent = (unsigned long *)ftrace_get_parent_addr(self_addr, old, > > + (unsigned long)parent, > > + fp); > > + > > + *parent = return_hooker; > > Although you may have turned off fgraph tracer in > ftrace_get_parent_addr, nothing stops the below from messing with the > stack. The return stack may get off sync and break later. If you fail > the above, you should not be calling the push function below. > We need to really stop before ftrace_push_return_trace to avoid messing with the stack :-) but if we have stopped the tracer, is it important to mess with the stack or not? Regards, Wu Zhangjin