[OE-core] [PATCH 1/2] goarch.bbclass: Define HOST_GO386 and TARGET_GO386

[Paul Barker]

On Sat, Oct 14, 2017 at 2:22 AM, Khem Raj <raj.khem at gmail.com> wrote:
> On Fri, Oct 13, 2017 at 12:25 PM, Paul Barker <pbarker at toganlabs.com> wrote:
>> These variables are used to control the floating-point instructions emitted by
>> the go compiler for x86 architectures.
>>
>> The default is '387' which disables the use of sse/sse2 instructions and is safe
>> to use on all x86 processors from the i486 onwards.
>>
>> If TUNE_FEATURES contains a feature set which is known to support sse/sse2
>> instructions then they are set to 'sse2' to enable the use of these
>> instructions. This is suitable for most processors from Pentium 4 onwards.
>>
>> Only the 'core2' and 'corei7' TUNE_FEATURES are defined in the oe-core layer and
>> are known to support ss2 instructions. Other layers may introduce additional
>> tunings which support sse2 instructions and for these layers, TARGET_GO386
>> or go_map_386 should be overridden as needed.
>>
>> Signed-off-by: Paul Barker <pbarker at toganlabs.com>
>> ---
>>  meta/classes/goarch.bbclass | 11 +++++++++++
>>  1 file changed, 11 insertions(+)
>>
>> diff --git a/meta/classes/goarch.bbclass b/meta/classes/goarch.bbclass
>> index 659b26a..653f035 100644
>> --- a/meta/classes/goarch.bbclass
>> +++ b/meta/classes/goarch.bbclass
>> @@ -4,10 +4,12 @@ BUILD_GOTUPLE = "${BUILD_GOOS}_${BUILD_GOARCH}"
>>  HOST_GOOS = "${@go_map_os(d.getVar('HOST_OS'), d)}"
>>  HOST_GOARCH = "${@go_map_arch(d.getVar('HOST_ARCH'), d)}"
>>  HOST_GOARM = "${@go_map_arm(d.getVar('HOST_ARCH'), d.getVar('TUNE_FEATURES'), d)}"
>> +HOST_GO386 = "${@go_map_386(d.getVar('HOST_ARCH'), d.getVar('TUNE_FEATURES'), d)}"
>>  HOST_GOTUPLE = "${HOST_GOOS}_${HOST_GOARCH}"
>>  TARGET_GOOS = "${@go_map_os(d.getVar('TARGET_OS'), d)}"
>>  TARGET_GOARCH = "${@go_map_arch(d.getVar('TARGET_ARCH'), d)}"
>>  TARGET_GOARM = "${@go_map_arm(d.getVar('TARGET_ARCH'), d.getVar('TUNE_FEATURES'), d)}"
>> +TARGET_GO386 = "${@go_map_386(d.getVar('TARGET_ARCH'), d.getVar('TUNE_FEATURES'), d)}"
>>  TARGET_GOTUPLE = "${TARGET_GOOS}_${TARGET_GOARCH}"
>>  GO_BUILD_BINDIR = "${@['bin/${HOST_GOTUPLE}','bin'][d.getVar('BUILD_GOTUPLE') == d.getVar('HOST_GOTUPLE')]}"
>>
>> @@ -66,6 +68,15 @@ def go_map_arm(a, f, d):
>>              return '5'
>>      return ''
>>
>> +def go_map_386(a, f, d):
>> +    import re
>> +    if re.match('i.86', a):
>> +        if ('core2' in f) or ('corei7' in f):
>> +            return 'sse2'
>> +        else:
>> +            return '387'
>> +    return ''
>> +
>
>
> This is too conservative IMO, e.g. anything above i586 is able to handle sse2
> with this patch i686 will use x87 for FPU,
>

The Go documentation says "Pentium 4/Opteron/Athlon 64 or later"
(https://golang.org/doc/install/source). GCC documentation also
suggests that i686 is too early to support SSE2:
https://gcc.gnu.org/onlinedocs/gcc/x86-Options.html#x86-Options. So I
think i686 should be using the old-style FPU instructions.

Cheers,

-- 
Paul Barker
Togán Labs Ltd