lang/rust: fix build on ppc64 and armv6/7

[mikael]

Summary

std_detect is missing on these arches.

Test Plan

untested on amd64

[jbeich]

• FreeBSD >= 12 should try elf_aux_info before KERN_PROC_AUXV, similar to how getauxval is tried before /proc/self/auxv on Linux
• AT_HWCAP is nop on powerpc64 on FreeBSD < 12, see rS332859; previous versions can use hw.cpu_features and hw.cpu_features2
• Upstreaming is necessary to avoid bitrot

Sorry, I don't know Rust to review the actual code.

lang/rust/files/patch-stdsimd

165

Why not aux.hwcap2? 0x80000000 in AT_HWCAP refers to PPC_FEATURE_32, not PPC_FEATURE2_ARCH_2_07.

[mikael]

In D19940#428579, @jbeich wrote:

• FreeBSD >= 12 should try elf_aux_info before KERN_PROC_AUXV, similar to how getauxval is tried before /proc/self/auxv on Linux

man elf_aux_info
No manual entry for elf_aux_info
-> not implemented

• AT_HWCAP is nop on powerpc64 on FreeBSD < 12, see rS332859; previous versions can use hw.cpu_features and hw.cpu_features2

It'll add a lot of code for a dead branch and only for one arch, it's not worth the effort.

• Upstreaming is necessary to avoid bitrot

sure.

Sorry, I don't know Rust to review the actual code.

that makes two of us

lang/rust/files/patch-stdsimd

165

congrats, you've found a bug in the linux code

[mikael]

fix hwcap2 on arm.rs and ppc

[jbeich]

In D19940#428596, @mikael.urankar_gmail.com wrote:

In D19940#428579, @jbeich wrote:

• FreeBSD >= 12 should try elf_aux_info before KERN_PROC_AUXV, similar to how getauxval is tried before /proc/self/auxv on Linux

man elf_aux_info
No manual entry for elf_aux_info
-> not implemented

See multimedia/libvpx/files/patch-vpx__ports_{arm,ppc}__cpudetect.c for NEON and VSX examples. As the 2nd argument to elf_aux_info is a pointer one has to be a bit more careful with types i.e., libc sanity checks aren't foolproof to avoid a crash.

CC @mmel per rS324815 and @ian per planned manpage.

[jbeich]

lang/rust/files/patch-stdsimd

166

2 was added to the wrong place: auxv2.hwcap -> auxv.hwcap2.

[tobik]

Can you send it upstream please? It's necessary anyway and they maybe able to review the actual Rust code.

[pkubaj]

I can confirm that with the attached patch I can build rust on stable/12 on powerpc64.

[• ian]

In D19940#428666, @jbeich wrote:

In D19940#428596, @mikael.urankar_gmail.com wrote:

In D19940#428579, @jbeich wrote:

• FreeBSD >= 12 should try elf_aux_info before KERN_PROC_AUXV, similar to how getauxval is tried before /proc/self/auxv on Linux

man elf_aux_info
No manual entry for elf_aux_info
-> not implemented

See multimedia/libvpx/files/patch-vpx__ports_{arm,ppc}__cpudetect.c for NEON and VSX examples. As the 2nd argument to elf_aux_info is a pointer one has to be a bit more careful with types i.e., libc sanity checks aren't foolproof to avoid a crash.

CC @mmel per rS324815 and @ian per planned manpage.

I had completely forgotten about writing that manpage. Better late than never, I guess, I just did it. See D20063

[tobik]

In D19940#431095, @pkubaj wrote:

I can confirm that with the attached patch I can build rust on stable/12 on powerpc64.

Ok. I've batched this up with the Rust 1.34.1 update and test builds were fine on amd64/i386, so I have no objections to add these patches to the port.