[ffi] Support 32-bit ARM.

[dcharkes]

Support dart:ffi on Arm and Android

[dcharkes]

Landed in d14dfc5.

[sjindel-google]

ARM32 support hasn't landed yet.

[sjindel-google]

Re-naming this issue to be more precise about the scope.
Nothing VM-specific needs to be done to accomodate Android anymore.

[dcharkes]

This landed in https://dart-review.googlesource.com/c/sdk/+/97631 2 months ago.

@sortie and I tried to import dart:ffi in arm32 on an arm64 linux device but it refused with import of dart:ffi with --enable-ffi=false. Using arm64 on the same device worked fine. This was Dart 2.4.0-dev.0.1.

I'm not sure why it should be disabled on arm32 Linux:

  static bool IsFfiEnabled() {
    // dart:ffi is not implemented for the following configurations
#if defined(TARGET_ARCH_DBC) && !defined(ARCH_IS_64_BIT)
    // TODO(36809): Support SimDBC32.
    return false;
#elif defined(TARGET_ARCH_DBC) &&                                              \
    !(defined(HOST_ARCH_X64) || defined(HOST_ARCH_ARM64))
    // TODO(36809): Support ia32 and arm.
    return false;
#elif defined(TARGET_ARCH_DBC) && defined(HOST_ARCH_X64) &&                    \
    defined(HOST_OS_WINDOWS)
    // TODO(35773): Support x64 Windows.
    return false;
#elif defined(TARGET_ARCH_ARM) &&                                              \
    !(defined(TARGET_OS_ANDROID) || defined(TARGET_OS_MACOS_IOS))
    // TODO(36309): Support hardfp calling convention.
    return false;
#elif !defined(TARGET_OS_LINUX) && !defined(TARGET_OS_MACOS) &&                \
    !defined(TARGET_OS_ANDROID) && !defined(TARGET_OS_WINDOWS)
    return false;
#else
    // dart:ffi is also not implemented for precompiled in which case
    // FLAG_enable_ffi is set to false by --precompilation.
    // Once dart:ffi is supported on all targets, only users will set this flag
    return FLAG_enable_ffi;
#endif
  }

@sjindel-google any thoughts on this?

[sjindel-google]

#36309