Date: Mon, 24 Oct 2011 16:47:42 +0300 From: Andriy Gapon <avg@FreeBSD.org> To: John Baldwin <jhb@FreeBSD.org> Cc: Pavel Timofeev <timp87@gmail.com>, freebsd-current@FreeBSD.org, Dennis Koegel <dk@neveragain.de> Subject: Re: Fresh installed Freebsd 9 don't boot from hd Message-ID: <4EA56C7E.1040005@FreeBSD.org> In-Reply-To: <201110240941.02515.jhb@freebsd.org> References: <CAAoTqftvv1t214Q9uWJR-Jug4GJEZshXyOr6uB_d19h2NV89XA@mail.gmail.com> <20111023152754.GA35505@neveragain.de> <4EA455A7.2060301@FreeBSD.org> <201110240941.02515.jhb@freebsd.org>
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on 24/10/2011 16:41 John Baldwin said the following: > On Sunday, October 23, 2011 1:57:59 pm Andriy Gapon wrote: >> on 23/10/2011 18:27 Dennis Koegel said the following: >>> On Fri, Oct 21, 2011 at 04:33:38PM -0400, John Baldwin wrote: >>>> Working offline with Dennis, we found that changing the CFLAGS in >>>> sys/boot/i386/gptboot/Makefile from "-O1" to "-Os -mrtd" (partially reverting >>>> an earlier commit) fixed gptboot. The next test for someone to do would be to >>>> try just adding "-mrtd" and leaving "-O1" as-is to see if that fixes it. >>> >>> More test results: >>> >>> gcc -Os -fno-guess-branch-probability -fomit-frame-pointer -fno-unit-at-a-time \ >>> -mno-align-long-strings -mrtd [from before r225530]: Boots OK >>> gcc -Os -mrtd: Boots OK >>> gcc -O1 -mrtd: Fails >>> gcc -O1: Fails >>> gcc -O0: Fails >>> gcc -Os: Boots OK >>> >>> clang -O1: Fails >>> clang -Os: Fails >>> clang -Oz: Fails >>> >>> I've put some printf()s into gpt{,boot}.c to trace where the reboot is >>> triggered. It appears to be in drvsize() (called from gptread()). OTOH >>> the debug output may have changed where the problem occurs, I don't >>> know about that. >>> >>> With 9.0R drawing near, CFLAGS should be s/-O1/-Os/, until we can figure >>> out what happens. But as for why gcc's magic -Os is required and clang's >>> output doesn't work at all, I'm clueless. >> >> Thank you for your very valuable analysis! >> I looked at a difference in assembly code of the drvsize function produced by >> gcc -Os and by gcc -O1. One thing that was immediately obvious is that gcc >> places the params array and the sectors variable in a different order for >> different options. One idea is that if BIOS actually writes beyond the end of >> the array, then in one case it could be harmless (overwrites the sector >> variable), but in the other case it could be more harmful. >> I found a document that suggests a possibility of BIOS writing more bytes to the >> array than its current size of 0x42: >> http://www.t13.org/documents/UploadedDocuments/docs2008/e08134r1-BIOS_Enhanced_Disk_Drive_Services_4.0.pdf >> >> Of course, the size of the array is passed to BIOS at the start of the array and >> so a _non-buggy_ BIOS should not write beyond the array, but we live in a >> non-perfect world. > > Hmm, I think we've had to do a similar workaround in the past for a different > BIOS call (SMAP maybe?). However, I do have one request, can we declare an > actual structure instead of a silly char array? Then we can remove the weird > casts with offsets into it, etc. Having an actual struct would be far more > readable and less bug-prone. > I am all for this. Unfortunately. ENOTIME to do this properly at the moment. -- Andriy Gapon
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