[U-Boot] armv5 and OMAP3 Question

Sat Aug 4 11:44:52 UTC 2018

On Sat, Aug 04, 2018 at 05:32:18AM -0500, Adam Ford wrote:
> On Fri, Aug 3, 2018 at 10:20 AM Tom Rini <trini at konsulko.com> wrote:
> >
> > On Fri, Aug 03, 2018 at 10:02:17AM -0500, Adam Ford wrote:
> > > On Fri, Aug 3, 2018 at 10:00 AM Tom Rini <trini at konsulko.com> wrote:
> > > >
> > > > On Fri, Aug 03, 2018 at 05:43:46AM -0500, Adam Ford wrote:
> > > > > On Tue, Jul 25, 2017 at 11:08 AM Tom Rini <trini at konsulko.com> wrote:
> > > > > >
> > > > > > On Tue, Jul 25, 2017 at 08:14:57AM -0500, Adam Ford wrote:
> > > > > >
> > > > > > > The readme file for OMAP indicates that we compile using armv5 to "to
> > > > > > > allow more compilers to work"
> > > > > > >
> > > > > > > We have our arch/arm/mach-omap2/omap3/lowlevel_init.S file also noting
> > > > > > > some special assembly insturctions becuse we use armv5.  The barriers
> > > > > > > defined also indicate we're using CP15 instead of the separate barrier
> > > > > > > instructions for armv7 because we're using armv5 instead.
> > > > > > >
> > > > > > > I just wonder in this day and age when we're noting a GCC version and
> > > > > > > generating warnings based on the GCC warning, do we still need to
> > > > > > > compile as armv5 any more?  It seems like "to allow more compilers to
> > > > > > > work" would not really apply any more we're trying to push newer
> > > > > > > versions of GCC.
> > > > > >
> > > > > > So, these are historical notes that really should be corrected.
> > > > > > Initially, when ARMv7 support was added, most people did not have
> > > > > > compilers new enough to recognize -march=armv7-a.  We still even support
> > > > > > them, see the logic in arch/arm/Makefile around CONFIG_CPU_V7 (the
> > > > > > options are any sort of modern gcc, llvm, ancient gcc).  When we move to
> > > > > > gcc-6 being the oldest gcc supported for ARM we can fixup those comments
> > > > > > and logic as well.
> > > > >
> > > > > My understanding is that we've made the requirement for GCC 6 now.  I
> > > > > just pushed a patch which enabled mtune=armv7-a-generic when
> > > > > CONFIG_CPU_V7A is enabled and that seems to shrink the code a bit on
> > > > > omap3_logic.  Does it make sense to remove the , -march=armv5 from
> > > > > arch/arm/Makefile and or the plain -march=armv7 since CONFIG_CPU_V7A
> > > > > implies armv-a?
> > > >
> > > > Yes, we can probably at least drop the v5 portion of that logic.  As
> > > > noted in the other patch, LLVM and GCC disagree on "armv7" vs "armv7-a"
> > > > as being the appropriate name, or at least did in the past.
> > >
> > > Can you point me to an example of how to tune armv7 for both GCC and
> > > LLVM?  I was looking around and I'm not seeing an obvious syntax.
> > > I'll do a 2-part patch.  One to remove the armv5, and one to enable
> > > the armv7 optimization.
> >
> > In arch/arm/Makefile:
> > arch-$(CONFIG_CPU_V7A)          =$(call cc-option, -march=armv7-a, \
> >                                  $(call cc-option, -march=armv7, -march=armv5))
> >
> > this works in both cases.  And doc/README.clang is correct on how to
> > build with LLVM on ARM.
> 
> I reset my head to origin/master, but using the following, I am not
> able to build omap3_logic with clang on Ubuntu 18.04:
> 
> make HOSTCC=clang omap3_logic
> make HOSTCC=clang CROSS_COMPILE=arm-linux-gnueabi- \
>     CC="clang -target arm-linux-gnueabi" -j8
> 
> arch/arm/lib/memset.S:43:2: error: predicated instructions must be in IT block
>  stmiage ip!, {r1, r3, r8, lr} @ 64 bytes at a time.
>  ^
> arch/arm/lib/memset.S:44:2: error: predicated instructions must be in IT block
>  stmiage ip!, {r1, r3, r8, lr}
>  ^
> arch/arm/lib/memset.S:45:2: error: predicated instructions must be in IT block
>  stmiage ip!, {r1, r3, r8, lr}
>  ^
> arch/arm/lib/memset.S:46:2: error: predicated instructions must be in IT block
>  stmiage ip!, {r1, r3, r8, lr}
>  ^
> arch/arm/lib/memset.S:48:2: error: predicated instructions must be in IT block
>  ldmfdeq sp!, {r8, pc} @ Now <64 bytes to go.
>  ^
> arch/arm/lib/memset.S:53:2: error: predicated instructions must be in IT block
>  stmiane ip!, {r1, r3, r8, lr}
>  ^
> arch/arm/lib/memset.S:54:2: error: predicated instructions must be in IT block
>  stmiane ip!, {r1, r3, r8, lr}
>  ^
> arch/arm/lib/memset.S:56:2: error: predicated instructions must be in IT block
>  stmiane ip!, {r1, r3, r8, lr}
>  ^
> arch/arm/lib/memset.S:103:2: error: predicated instructions must be in IT block
>  stmiane ip!, {r1, r3}
>  ^
> arch/arm/lib/memset.S:105:2: error: predicated instructions must be in IT block
>  strne r1, [ip], #4
>  ^
> arch/arm/lib/memset.S:111:2: error: predicated instructions must be in IT block
>  strbne r1, [ip], #1
>  ^
> arch/arm/lib/memset.S:112:2: error: predicated instructions must be in IT block
>  strbne r1, [ip], #1
>  ^
> arch/arm/lib/memset.S:114:2: error: predicated instructions must be in IT block
>  strbne r1, [ip], #1
>  ^
> arch/arm/lib/memset.S:120:2: error: predicated instructions must be in IT block
>  strblt r1, [ip], #1 @ 1
>  ^
> arch/arm/lib/memset.S:121:2: error: predicated instructions must be in IT block
>  strble r1, [ip], #1 @ 1
>  ^
> scripts/Makefile.build:314: recipe for target 'arch/arm/lib/memset.o' failed
> make[1]: *** [arch/arm/lib/memset.o] Error 1
> Makefile:1373: recipe for target 'arch/arm/lib' failed
> make: *** [arch/arm/lib] Error 2
> aford at aford-IdeaCentre-A730:~/src/u-boot$
> 
> If you have any suggestions, I'm open to try them.  I have never used
> clang before, but  I would really like to get these armv7a
> optimizations in to make SPL smaller.

I guess I forgot that you will need to turn off ARCH_MEMCPY/ARCH_MEMSET
and EFI support for clang.  That said, since you're just making sure the
right options are being passed in, in both cases, you can also just use
V=1 and just build common/main.o or something like that.

-- 
Tom
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