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Re: GCC default CPUs
On 30/10/2018 21:13, coypu%sdf.org@localhost wrote:
hi port-arm,
i'm upstreaming the netbsd eabi target to gcc upstream.
a question came up about our choice of platform triplets (or is it
fourlets?:)), there are quite many.
armv4--netbsdelf-eabi
armv6--netbsdelf-eabi
armv7--netbsdelf-eabi
arm*--netbsdelf-eabi ??
also,
arm--netbsdelf, for OABI.
The first part should affect default cpu for the configuration.
In base and in upstream, given the current patch, it will be:
ISA ver | Base GCC | upstream GCC
--------------------------------------------------------------------
v4 | strongarm | strongarm
v6 | arm1176jzf-s | arm1176jzf-s
v7 | cortex-a8 | generic-armv7-a[1]
else | arm6 ? (not 100% sure) | strongarm[2]
Did you see
http://src.illumos.org/source/xref/netbsd-src/external/gpl3/gcc/dist/gcc/config/arm/netbsd-elf.h#30
30 /* Default EABI to armv5t so that thumb shared libraries work.
31 The ARM926EH-S core is the default for armv5te, so set
32 SUBTARGET_CPU_DEFAULT to achieve this. */
33
34 #define SUBTARGET_CPU_DEFAULT \
35 (ARM_DEFAULT_ABI != ARM_ABI_APCS && ARM_DEFAULT_ABI != ARM_ABI_ATPCS \
36 ? TARGET_CPU_arm926ejs : TARGET_CPU_arm6)
the question was: why did we make these choices?
I assume a CPU with Thumb support in each architecture version. I see
rearnshaw mostly agrees with the choices in the gcc list discussion.
if i had to come up with a policy, it'd be "create a target for every
time ARM decides you can break ISA compatibility, use -mcpu otherwise".
We have enough targets already. I don't think we need more.
i guess armv6 exists for RPI1 alone and people did not want to
compromise for everything else?
arm6 != armv6. I theory acorn32 runs on arm6.
Please send patches to port-arm for approval if there is a change to
base to match proposed upstream.
Nick
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