[yocto] Tuning for a machine based on Cortex-A9

[Khem Raj]

> On Aug 24, 2016, at 12:51 AM, Ottavio Campana <o.campana at videotec.com> wrote:
> 
> Hello,
> 
> I am trying to port a third-party BSP based on buildroot to yocto, but I am not able to tune the compiler to extactly match the original one.
> 
> Particularly, if I run readelf on a binary compiled with the gcc that is used by buildroot I get this output
> 
> ottavio at ottavio:~$ readelf -A hello_world
> Attribute Section: aeabi
> File Attributes
>   Tag_CPU_name: "Cortex-A9"
>   Tag_CPU_arch: v7
>   Tag_CPU_arch_profile: Application
>   Tag_ARM_ISA_use: Yes
>   Tag_THUMB_ISA_use: Thumb-2
>   Tag_FP_arch: VFPv3
>   Tag_Advanced_SIMD_arch: NEONv1
>   Tag_ABI_PCS_wchar_t: 4
>   Tag_ABI_FP_rounding: Needed
>   Tag_ABI_FP_denormal: Needed
>   Tag_ABI_FP_exceptions: Needed
>   Tag_ABI_FP_number_model: IEEE 754
>   Tag_ABI_align_needed: 8-byte
>   Tag_ABI_align_preserved: 8-byte, except leaf SP
>   Tag_ABI_enum_size: int
>   Tag_CPU_unaligned_access: v6
>   Tag_MPextension_use: Allowed
>   Tag_Virtualization_use: TrustZone
> ottavio at ottavio:~$
> 
> I tried to replicate this by configuring a new machine, and my machine configuration looks like this
> 
> require ../../../meta/conf/machine/include/tune-cortexa9.inc
> 
> AVAILTUNES += "cortexa9t-vfpv3-neon"
> ARMPKGARCH_tune-cortexa9t-vfpv3-neon          = "cortexa9"
> TUNE_FEATURES_tune-cortexa9t-vfpv3-neon       = "${TUNE_FEATURES_tune-armv7at-vfpv3} neon cortexa9"
> PACKAGE_EXTRA_ARCHS_tune-cortexa9t-vfpv3-neon = "${PACKAGE_EXTRA_ARCHS_tune-armv7at-vfpv3} cortexa9-vfp cortexa9-vfpv3 cortexa9t2-vfp cortexa9t2-vfpv3 cortexa9-neon"
> 
> DEFAULTTUNE = "cortexa9t-vfpv3-neon”

Use

 DEFAULTTUNE = "cortexa9t-neon"

if you want to use hard-float ABI then

DEFAULTTUNE = “cortexa9thf-neon"

> 
> If I run readelf on any compiled binary obtained with yocto, I get this result:
> 
> ottavio at ottavio:~/poky/build-xxx/tmp/work/cortexa9-vfpv3-poky-linux-gnueabi/bzip2/1.0.6-r5/build$ readelf -A .libs/bzip2
> Attribute Section: aeabi
> File Attributes
>   Tag_CPU_name: "Cortex-A9"
>   Tag_CPU_arch: v7
>   Tag_CPU_arch_profile: Application
>   Tag_ARM_ISA_use: Yes
>   Tag_THUMB_ISA_use: Thumb-2
>   Tag_FP_arch: VFPv3
>   Tag_ABI_PCS_wchar_t: 4
>   Tag_ABI_FP_rounding: Needed
>   Tag_ABI_FP_denormal: Needed
>   Tag_ABI_FP_exceptions: Needed
>   Tag_ABI_FP_number_model: IEEE 754
>   Tag_ABI_align_needed: 8-byte
>   Tag_ABI_align_preserved: 8-byte, except leaf SP
>   Tag_ABI_enum_size: int
>   Tag_CPU_unaligned_access: v6
>   Tag_MPextension_use: Allowed
>   Tag_Virtualization_use: TrustZone
> ottavio at ottavio:~/poky/build-xxx/tmp/work/cortexa9-vfpv3-poky-linux-gnueabi/bzip2/1.0.6-r5/build$
> 
> I am quite close to get a similar binary, the missing part is the Tag_Advanced_SIMD_arch: NEONv1 .  I get exactly the same result if I use DEFAULTTUNE = "cortexa9t-vfpv3", thus it seems that the neon and cortexa9-neon options I tried to add are ignored.
> 
> At this point I have two questions
> 
> Question #1
> 
> How should I change ARMPKGARCH_tune-cortexa9t-vfpv3-neon , TUNE_FEATURES_tune-cortexa9t-vfpv3-neon and PACKAGE_EXTRA_ARCHS_tune-cortexa9t-vfpv3-neon to have exactly the same kind of elf?
> 
> Question # 2
> 
> Why the only options for neon in meta/conf/machine/include/tune-cortexa9.inc are offered for HF tunes?
> 
> 
> Thank you for your help
> 
> Ottavio
> --
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