Date: Fri, 10 Jan 2014 16:41:27 -0700 From: Ian Lepore <ian@FreeBSD.org> To: John-Mark Gurney <jmg@funkthat.com> Cc: andrew@FreeBSD.org, freebsd-arm@FreeBSD.org Subject: Re: svn commit: r258412 - in head/sys/arm: at91 econa s3c2xx0 sa11x0 xscale/i80321 xscale/i8134x xscale/ixp425 xscale/pxa Message-ID: <1389397287.1158.462.camel@revolution.hippie.lan> In-Reply-To: <20140110230241.GS46596@funkthat.com> References: <201311210108.rAL18AoQ051365@svn.freebsd.org> <20131221061048.GC99167@funkthat.com> <20140108071643.GB99167@funkthat.com> <1389197091.1158.370.camel@revolution.hippie.lan> <20140108173909.GF99167@funkthat.com> <20140110230241.GS46596@funkthat.com>
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On Fri, 2014-01-10 at 15:02 -0800, John-Mark Gurney wrote:
> John-Mark Gurney wrote this message on Wed, Jan 08, 2014 at 09:39 -0800:
> > So, I've tested that HEAD (absolutely no tree changes) w/
> > WITHOUT_ARM_EABI boots fine... and just to make sure my test is
> > correct, I've disabled it too to verify that the kernel just hangs
> > (absolutely no output).. and reenabled it and verified it works (that
> > my setting is changing something)...
> > worky -> no worky -> worky...
> >
> > Now I just realized another interesting thing about setting
> > WITHOUT_ARM_EABI, it also fixes the console issue I was having w/ your
> > call to cpu_setup("") previously (w/ EABI) killing console output and
> > not even seeing the mtx panic message...
> >
> > So, it is clearly changing something very early on in boot...
>
> Apparently gcc ARMEB w/ EABI miscompiles code... The code to store
> lo_flags in the lock_object is correct:
> lock->lo_flags = i << LO_CLASSSHIFT;
> c03ce2d0: e1a01c06 lsl r1, r6, #24
> c03ce2d4: e5881004 str r1, [r8, #4]
>
> But when I add a printf to fetch the data, I get:
> printf("lo_classindex: %#x\n", LO_CLASSINDEX(lock));
> c03ce2e0: e5d81007 ldrb r1, [r8, #7]
> c03ce2e4: e59f0098 ldr r0, [pc, #152] ; c03ce384 <_end+0xffcf9
> 19c>
> c03ce2e8: e201100f and r1, r1, #15 ; 0xf
> c03ce2ec: eb0012ea bl c03d2e9c <printf>
>
>
> We are doing a ldrb (LoaD Relative Byte) which would be fine to
> substitute for the right shift of 24, but only if it loaded the correct
> byte.. It should be loading #4 instead of #7 since we are on big
> endian...
>
> Anyone who know gcc arm well to figure this out?
>
The generated byte-load code is enough different from the literal "load
32 bits and shift" of LO_CLASSINDEX() that the optimizer must have
messed it up. Do we build the kernel with -O2, and if so would -O1
help?
-- Ian
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