Invalid Instruction - aarch64 with armv8-a (Raspberry Pi 4)

[adasek]

Hi,
I'm running typescript linting a Raspberry Pi 4 system and recently some Rust compiled libraries were added to my stack and it started to fail with:

Illegal instruction (exit code 132)

I reported the issue to the packages unrs-resolver and oxc-project but after a deeper research I believe the problem is in mimalloc.

When compiling mimaloc on my system, -march=armv8.1-a is used and it causes mi_atomic_add_acq_rel aka atomic_fetch_add_explicit call to be compiled as ldaddal instruction that's unsupported by my system - Rpi4 is apparently armv8-a.

I've checked the issue persist on another Raspberry Pi 4 hardware with a clean Raspbian 64bit installation. Similar failure on aarch64 AWS EC2 instance was also reported

A most straightforward fix would be to change

mimalloc/CMakeLists.txt

Line 442 in d2e259c

set(MI_OPT_ARCH_FLAGS "-march=armv8.1-a") # fast atomics

from armv8.1-a to armv8-a. Using a minimal mimalloc usage example I verified that it fixes my problem, but it will mean a performance drop in aarch64 systems supporting armv8.1-a, so I'm seeking for some more precise way.

Let me know if you need any more information or testing.

[jimying]

Use -DMI_NO_OPT_ARCH=OFF can fix the build error, but don't known is it affect performance?

[daanx]

Hi @jimying -- you should use -DMI_OPT_ARCH=OFF (note: not -DMI_NO_OPT_ARCH=OFF). Yes, it will be slightly worse performance but if the processor doesn't support the newer instructions, well, then nothing can be done.

[SandaruKasa]

you should use -DMI_OPT_ARCH=OFF (note: not -DMI_NO_OPT_ARCH=OFF)

Seems like -DMI_NO_OPT_ARCH=ON should actually be used instead to not get overridden by cmake.

[daanx]

you should use -DMI_OPT_ARCH=OFF (note: not -DMI_NO_OPT_ARCH=OFF)

Seems like -DMI_NO_OPT_ARCH=ON should actually be used instead to not get overridden by cmake.

Well, that option is really only meant for vcpkg options to override the default. But in regular cmake use you can just use -DMI_OPT_ARCH=OFF.