linux-kernel - Re: Build regressions/improvements in v4.9-rc1

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Date:   Thu, 27 Oct 2016 11:24:07 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
Cc:     Alexey Brodkin <Alexey.Brodkin@...opsys.com>,
        "mpe@...erman.id.au" <mpe@...erman.id.au>,
        "linux-snps-arc@...ts.infradead.org" 
        <linux-snps-arc@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "Vineet.Gupta1@...opsys.com" <Vineet.Gupta1@...opsys.com>,
        "arnd@...db.de" <arnd@...db.de>, "mmarek@...e.cz" <mmarek@...e.cz>
Subject: Re: Build regressions/improvements in v4.9-rc1

On Thu, Oct 27, 2016 at 11:11 AM, Thomas Petazzoni
<thomas.petazzoni@...e-electrons.com> wrote:
> On Thu, 27 Oct 2016 09:07:55 +0000, Alexey Brodkin wrote:
>
>> > axs101 is using a 770 core, while the toolchain is built for the HS38
>> > core. I'm somewhat surprised that a single ARC toolchain cannot produce
>> > code for both 770 and HS38, but it seems to be the case.
>> >
>> > So you need a separate toolchain for ARC770.
>>
>> Indeed axs101 uses ARC770 core which is ARCv1 AKA ARCompact ISA while
>> axs103 sports the same base-board but CPU daughter-card contains ARC HS38 core
>> which has ARCv2 ISA (binary incompatible with ARCompact).
>>
>> Essentially both gcc and binutils will happily build for both architectures given
>> proper options were passed on the command line. But Linux kernel gets linked with
>> pre-built libgcc (it is a part of toolchain). And so it all boils down to a requirement
>> to have multilibbed uClibc toolchain. Which we don't have.
>
> Interesting. Why is libgcc linked with the kernel on ARC? I don't think
> that's the case on other architectures: the kernel is freestanding and
> provides everything that it needs without relying on the compiler
> runtime.

ARC is not the only one:

$ git grep print-libgcc-file-name
arch/arc/Makefile:LIBGCC := $(shell $(CC) $(cflags-y) --print-libgcc-file-name)
arch/h8300/boot/compressed/Makefile:LIBGCC := $(shell
$(CROSS-COMPILE)$(CC) $(KBUILD_CFLAGS) -print-libgcc-file-name)
arch/hexagon/Makefile:LIBGCC := $(shell $(CC) $(KBUILD_CFLAGS)
-print-libgcc-file-name)
arch/m32r/Makefile:LIBGCC := $(shell $(CC) $(KBUILD_CFLAGS)
-print-libgcc-file-name)
arch/nios2/Makefile:LIBGCC         := $(shell $(CC) $(KBUILD_CFLAGS)
$(KCFLAGS) -print-libgcc-file-name)
arch/openrisc/Makefile:LIBGCC := $(shell $(CC) $(KBUILD_CFLAGS)
-print-libgcc-file-name)
arch/parisc/Makefile:LIBGCC = $(shell $(CC) $(KBUILD_CFLAGS)
-print-libgcc-file-name)
arch/tile/Makefile:  $(shell $(CC) $(KBUILD_CFLAGS) $(KCFLAGS)
-print-libgcc-file-name)
arch/xtensa/Makefile:LIBGCC := $(shell $(CC) $(KBUILD_CFLAGS)
-print-libgcc-file-name)
arch/xtensa/boot/boot-redboot/Makefile:LIBGCC := $(shell $(CC)
$(KBUILD_CFLAGS) -print-libgcc-file-name)

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds