Cann't build for armv7 with "neon"

[Dirreke]

Zig Version

0.9.1

Steps to Reproduce and Observed Behavior

I use zig c++ -target arm-linux-gnueabihf -mcpu=generic+v7a+vfp3+d32+thumb2+neon -mfpu=neon -mfloat-abi=hard
and it still cann't add neon to target-feature, and I always get this

/opt/zig/zig-linux-x86_64-0.9.1/lib/include/arm_neon.h:32:2: error: "NEON support not enabled"

Is it a bug? Or maybe I just missed some args?

Expected Behavior

//

[leecannon]

do you have the same issue with the latest stable zig release 0.10.1?

[Dirreke]

I cann't build for arm with 0.10.1 because #6573

  cargo:warning=warning(compilation): libc++ does not work on multi-threaded ARM yet.
  cargo:warning=For more details: https://github.com/ziglang/zig/issues/6573
  cargo:warning=error: unable to create compilation: TargetRequiresSingleThreaded
  exit status: 1

is there any way to build like rocksdb or Cbc with zig 0.10.1?

[iacore]

is there any way to build like rocksdb or Cbc with zig 0.10.1?

Can you use Clang?

[andrewrk]

Zig is indeed passing the neon flags to Clang, so the question is why doesn't clang define the macro?

#if !defined(__ARM_NEON)
#error "NEON support not enabled"
#else

Can you file a bug report on Clang? Use ZIG_VERBOSE_CC=1 to observe the clang command that zig spits out (which includes -Xclang +neon) and ask them why __ARM_NEON is not defined.

[Dirreke]

I'd love to try it. However, I'm a little busy these days. I will try to find this bug some days later.

[Dirreke]

It issue seems very related to #10411

[ldube]

(Tested on zig version 0.14.0-dev.1511+54b668f8a)

64bit ARMv8 defines __ARM_NEON and 32bit ARMv7 defines __ARM_FEATURE_SIMD32.

I used the commands below.

zig c++ -target aarch64-linux-gnueabihf  -x  c /dev/null -dM -E | grep -e SIMD -e NEON
#define __ARM_NEON 1
#define __ARM_NEON_FP 0xE

zig c++ -target arm-linux-gnueabihf  -x  c /dev/null -dM -E | grep -e SIMD -e NEON
#define __ARM_FEATURE_SIMD32 1

[alexrp]

It seems that arm_neon.h now checks for __ARM_FP. Is it usable now?

[ldube]

No. __ARM_NEON is checked because __ARM_FP is defined.

To make the program at the end compile, the check would have to be changed to this:
#if !defined(__ARM_NEON) && !defined(__ARM_FEATURE_SIMD32)

zig c++ -target arm-linux-gnueabihf -c hello.cpp

#include <arm_neon.h>

poly8x8_t atest(void) {
  poly8x8_t a;
  return splat_lane_p8(a, 0);
}

[alexrp]

__ARM_NEON is checked

Where?

To make the program at the end compile

It compiles for me with those flags.

[ldube]

I probably have an outdated build. I'll update and try again.

[alexrp]

0.14.0-dev.1659+4ceefca14 here FWIW.

[ldube]

Works with 0.14.0-dev.1651+ffd071f55