linux-kernel - Re: [PATCH 1/7] RISC-V: Top-Level Makefile for riscv{32,64}

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Date:   Fri, 26 May 2017 17:57:14 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...belt.com>
To:     Arnd Bergmann <arnd@...db.de>
CC:     albert@...ive.com
Subject:     Re: [PATCH 1/7] RISC-V: Top-Level Makefile for riscv{32,64}

On Tue, 23 May 2017 04:30:50 PDT (-0700), Arnd Bergmann wrote:
> On Tue, May 23, 2017 at 2:41 AM, Palmer Dabbelt <palmer@...belt.com> wrote:
>> RISC-V has both 32-bit and 64-bit base ISAs, but they are very similar.
>> Like some other platforms, we'd like to share one arch directory between
>> the two of them.
>
> I think we mainly do the others for backwards-compatibility with ancient
> build scripts, and we don't need that here. Instead, you could add one more
> line to the 'SUBARCH:=' statement that interprets the uname output.

I don't think that does the same thing.  The desired effect of this diff is:

 * "uname -m" when running on a RISC-V machine returns either riscv32 or
   riscv64, as that's what tools like autoconf expect when trying to find
   tuples.

 * I can cross compile for riscv32 and riscv64.  That's currently controlled by
   a Kconfig setting, but ARCH=riscv32 vs ARCH=riscv64 controlls what defconfig
   sets.

 * I can natively compile for riscv32 and riscv64.  That uses the same Kconfig
   setting, and the same ARCH=riscv32 vs ARCH=riscv64 switch for defconfig.

Neither of the two Kconfig issues is a big deal, but we de need "uname -m" to
return "riscv64" or "riscv32" not "riscv".  I think the only way to do that is
to set SRCARCH, but I'd be happy to change it if there's a better way.  I think
if I just do this

diff --git a/Makefile b/Makefile
index 0606f28..4adc609 100644
--- a/Makefile
+++ b/Makefile
@@ -232,7 +232,8 @@ SUBARCH := $(shell uname -m | sed -e s/i.86/x86/ -e s/x86_64/x86/ \
                                  -e s/arm.*/arm/ -e s/sa110/arm/ \
                                  -e s/s390x/s390/ -e s/parisc64/parisc/ \
                                  -e s/ppc.*/powerpc/ -e s/mips.*/mips/ \
-                                 -e s/sh[234].*/sh/ -e s/aarch64.*/arm64/ )
+                                 -e s/sh[234].*/sh/ -e s/aarch64.*/arm64/ \
+                                 -e s/riscv.*/riscv/ )

 # Cross compiling and selecting different set of gcc/bin-utils
 # ---------------------------------------------------------------------------
@@ -269,14 +270,6 @@ ifeq ($(ARCH),x86_64)
         SRCARCH := x86
 endif

-# Additional ARCH settings for RISC-V
-ifeq ($(ARCH),riscv32)
-       SRCARCH := riscv
-endif
-ifeq ($(ARCH),riscv64)
-       SRCARCH := riscv
-endif
-
 # Additional ARCH settings for sparc
 ifeq ($(ARCH),sparc32)
        SRCARCH := sparc

then I'll end up with "uname -m" as "riscv" -- I haven't tried it, but that's
why we ended up with this diff in the first place.