Date: Fri, 9 Dec 2011 12:49:57 -0500 From: Arnaud Lacombe <lacombar@gmail.com> To: Rafal Jaworowski <raj@semihalf.com> Cc: freebsd-hackers@freebsd.org, Gleb Kurtsou <gleb.kurtsou@gmail.com>, Nathan Whitehorn <nwhitehorn@freebsd.org>, mdf@freebsd.org, Piotr Nowak <pn@semihalf.com> Subject: Re: gcc 4.2 miscompilation with -O2 -fno-omit-frame-pointer on amd64 Message-ID: <CACqU3MVO-oWso%2BF4G%2BRP4d%2By761=-Oz3COt2ubDogdBK834jEA@mail.gmail.com> In-Reply-To: <6D023449-EDEA-4B1C-975D-54AA2F4328CE@semihalf.com> References: <20111119100150.GA1560@reks> <CACqU3MXf%2BsbTpZMbqugmMKKb1BEbp6sNzeTkXfvnQtZ1E4ukEA@mail.gmail.com> <BA73AB23-650A-4241-BBAC-BA01BD372AA3@semihalf.com> <20111208090159.GA1924@cq1> <4EE0EB8C.7050800@freebsd.org> <6D023449-EDEA-4B1C-975D-54AA2F4328CE@semihalf.com>
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Hi, On Fri, Dec 9, 2011 at 10:15 AM, Rafal Jaworowski <raj@semihalf.com> wrote: > > On 2011-12-08, at 17:53, Nathan Whitehorn wrote: > >> On 12/08/11 03:01, Piotr Nowak wrote: >>> We're working on PowerPC target using GCC 4.2.1 >>> and FreeBSD 6.1. It seems like we have similar >>> problem. In our case GCC sometimes very unfortunately >>> optimize code with -fno-omit-frame-pointer. >>> >>> Example shown below covers file sys/powerc/booke/pmap.c >>> and function pmap_kenter. If we disassemble kernel binary >>> we have: >>> >>> c019998c: 4b ec 6a ed bl c0060478<_mtx_unlock_spin_flags> >>> c0199990: 81 61 00 00 lwz r11,0(r1) >>> c0199994: 80 0b 00 04 lwz r0,4(r11) >>> c0199998: 7d 61 5b 78 mr r1,r11 >>> c019999c: 82 ab ff d4 lwz r21,-44(r11) >>> c01999a0: 7c 08 03 a6 mtlr r0 >>> c01999a4: 82 cb ff d8 lwz r22,-40(r11) >>> c01999a8: 82 eb ff dc lwz r23,-36(r11) >>> c01999ac: 83 0b ff e0 lwz r24,-32(r11) >>> c01999b0: 83 2b ff e4 lwz r25,-28(r11) >>> c01999b4: 83 4b ff e8 lwz r26,-24(r11) >>> c01999b8: 83 6b ff ec lwz r27,-20(r11) >>> >>> As you can see stack pointer on R1 is being updated >>> before stashed data were pulled off stack. (mr r1,r11) >>> As a result of this we have chance to get crash when >>> any interrupt hit shortly after stack pointer update. >>> The interrupt prologue will override not yet pulled off >>> pmap_kenter function data. >>> >>> The problem occures only with -fno-omit-frame-pointer >>> and not every branch returns are beeing corrupted. >>> >>> Do you think this issue may be somehow related to yours? >>> Are there any patches/solutions to fix it? >> >> Should we turn off -fno-omit-frame-frame-pointer on PPC then? It's enabled in default kernel builds. > > I think that's a good idea. Even though we have managed to trigger this only in rare cases, the problem is real and the code generated is broken i.e. leads to corruption and panics. > How can you make any conclusion without having seen a single line of code actually triggering the problem ? That sounds very irresponsible... - Arnaud
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