Date: Fri, 10 Jan 2014 16:26:48 -0800 From: John-Mark Gurney <jmg@funkthat.com> To: Ian Lepore <ian@FreeBSD.org> 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: <20140111002648.GT46596@funkthat.com> In-Reply-To: <1389397287.1158.462.camel@revolution.hippie.lan> 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> <1389397287.1158.462.camel@revolution.hippie.lan>
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Ian Lepore wrote this message on Fri, Jan 10, 2014 at 16:41 -0700:
> 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?
In a generated test case, even -O1 produces broken code... Only -O0
looks like it produces correct code, though the code is so much more
verbose, it takes more work to verify...
code:
int
foo(int *b)
{
return (*b & 0xf000000) >> 24;
}
-O0:
00000000 <foo>:
0: e1a0c00d mov ip, sp
4: e92dd800 push {fp, ip, lr, pc}
8: e24cb004 sub fp, ip, #4 ; 0x4
c: e24dd004 sub sp, sp, #4 ; 0x4
10: e50b0010 str r0, [fp, #-16]
14: e51b3010 ldr r3, [fp, #-16]
18: e5933000 ldr r3, [r3]
1c: e203340f and r3, r3, #251658240 ; 0xf000000
20: e1a03c43 asr r3, r3, #24
24: e1a00003 mov r0, r3
28: e89da808 ldm sp, {r3, fp, sp, pc}
-O1 & -O2:
00000000 <foo>:
0: e5d00000 ldrb r0, [r0]
4: e200000f and r0, r0, #15 ; 0xf
8: e12fff1e bx lr
--
John-Mark Gurney Voice: +1 415 225 5579
"All that I will do, has been done, All that I have, has not."
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