Question: can we build armv6 ABI for Alpine Linux using this toolchain

[ghost]

Apologies in advance if it is unrelated. We are trying to figure out how to get armv7-alpine-linux-musleabihf for Alpine Linux ARM32 v7 at https://github.com/dotnet/coreclr/issues/17468. The supported ABI by dotnet runtime atm is v7 for 32 bits and v8 for 64.

Since Alpine Linux armhf only provides armv6-alpine-linux-musleabihf for 32-bits targets (armv6 and armv7 devices), we were hoping to compile it ourselves; if possible.

Is this the right place to start? If not, could you suggest what would be the good place to start (if it is possible at all)?

Thanks!

[richfelker]

I don't understand what you're asking for. It sounds like you think armv6 and armv7 are different ABIs; they're not. They're just different ISA levels. A toolchain targeting armv6 produces binaries/libraries that are perfectly interlinkable with armv7 ones and vice versa; the only difference is whether additional armv7-only instructions are used (in which case the code only runs on armv7 and up as opposed to armv6 and up). If you have a toolchain targeting armv6, just adding -march=armv7-a to the CFLAGS will produce binaries optimized for armv7 (at the expense of being able to run on v6).

[ghost]

@richfelker, thanks for the information. I now get the concept of ABI compatibility between armv6 and armv7. :)

If Alpine distro only provides armv6-alpine-linux-musleabihf and CoreCLR codebase uses armv7-only instructions (dmb ish etc.), is there a way for us to still build CoreCLR in Alpine targeting ARMv7? https://pkgs.alpinelinux.org/contents?file=armv*&path=&name=&branch=edge&arch=armhf. In this case, do we need to still compile the toolchain (musl-cross-make) by ourselves with TARGET = armv7-linux-musleabihf, then using that toolchain compile CoreCLR repo (that also requires a different compiler; LLVM/clang)?

[richfelker]

You don't need a custom toolchain to do this, just -march=armv7-a.

[ghost]

Thanks. I tried sessing CFLAGS in CMake: set(CMAKE_C_FLAGS_INIT "${CMAKE_C_FLAGS_INIT} -march=armvv7-a -mcpu=cortex-a8") for alpine, however, when compiling on Alpine Linux 3.7 Linux aaf28ea95614 4.9.87-linuxkit-aufs #1 SMP Wed Mar 14 15:12:16 UTC 2018 armv7l Linux, I am still running into same invalid instructions error:

/coreclr/src/pal/../inc/volatile.h:154:5: error: invalid operand for instruction
    VOLATILE_MEMORY_BARRIER();
    ^
/coreclr/src/pal/../inc/volatile.h:79:49: note: expanded from macro 'VOLATILE_MEMORY_BARRIER'
#define VOLATILE_MEMORY_BARRIER() asm volatile ("dmb ish" : : : "memory")
                                                ^
<inline asm>:1:6: note: instantiated into assembly here
        dmb ish
            ^
1 error generated.

[ghost]

I made a simple test:

#include <stdio.h>
int main()
{
   asm volatile ("dmb ish" : : : "memory");
   return 0;
}

compiled with clang test.c -o test.exe -march=armv7-a, and it worked (without -march=armv7-a, it gives the error). It seems like something is wrong with CMake configuration of the project I am trying to build (something is overwriting CFlag). I will check.

Thanks for your help!