Date: Thu, 08 Dec 2011 10:53:32 -0600 From: Nathan Whitehorn <nwhitehorn@freebsd.org> To: Piotr Nowak <pn@semihalf.com> Cc: Rafal Jaworowski <raj@semihalf.com>, Gleb Kurtsou <gleb.kurtsou@gmail.com>, mdf@freebsd.org, Arnaud Lacombe <lacombar@gmail.com>, freebsd-hackers@freebsd.org Subject: Re: gcc 4.2 miscompilation with -O2 -fno-omit-frame-pointer on amd64 Message-ID: <4EE0EB8C.7050800@freebsd.org> In-Reply-To: <20111208090159.GA1924@cq1> References: <20111119100150.GA1560@reks> <CACqU3MXf%2BsbTpZMbqugmMKKb1BEbp6sNzeTkXfvnQtZ1E4ukEA@mail.gmail.com> <BA73AB23-650A-4241-BBAC-BA01BD372AA3@semihalf.com> <20111208090159.GA1924@cq1>
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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. -Nathan
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