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

[Ottavio Campana]

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"

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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