travis: Add some arm builds

[maflcko]

Proof of concept for #598

Not sure which environment combinations make most sense (something with ASM?)

[sipa]

We have optimized assembly for 32-bit ARM (not enabled by default, and not 64-bit iirc). It'd be neat to test that.

[maflcko]

ok, I set ASM=arm, but that fails:

$ if [ -n "$BUILD" ]; then make -j2 $BUILD; fi

  CC       src/bench_verify.o

  CC       src/bench_sign.o

  CC       src/exhaustive_tests-tests_exhaustive.o

gcc -I. -I./src -g -O2 -Wall -Wextra -Wno-unused-function -c src/gen_context.c -o gen_context.o

  CCAS     src/asm/field_10x26_arm.lo

src/asm/field_10x26_arm.s: Assembler messages:

src/asm/field_10x26_arm.s:1: Error: junk at end of line, first unrecognized character is `@'

src/asm/field_10x26_arm.s:18: Error: unknown pseudo-op: `.syntax'

src/asm/field_10x26_arm.s:19: Error: junk at end of line, first unrecognized character is `@'

src/asm/field_10x26_arm.s:20: Error: unknown pseudo-op: `.eabi_attribute'

src/asm/field_10x26_arm.s:21: Error: unknown pseudo-op: `.eabi_attribute'

src/asm/field_10x26_arm.s:24: Error: junk at end of line, first unrecognized character is `@'

src/asm/field_10x26_arm.s:27: Error: junk at end of line, first unrecognized character is `@'
...

See https://travis-ci.org/MarcoFalke/secp256k1/builds/621315153

[elichai]

Tried that in the past and couldn't make the asm work.
Hope you will :)

[real-or-random]

I haven't had a closer look now but this may help to figure out the right flags (even though it's for cross-compilation)
#621 (comment)

[laanwj]

I think you get those errors when trying to compile the 32-bit ARM assembly with a 64-bit targeted assembler.

[maflcko]

I might need to install libc from armhf. That doesn't work, so I reported the issue to travis: https://travis-ci.community/t/apt-addon-does-not-work-for-armhf-on-arm64/6374

[real-or-random]

Did this work in the end? The travis output looks good, it was just aborted?

[maflcko]

It failed with

/usr/lib/gcc-cross/arm-linux-gnueabihf/5/../../../../arm-linux-gnueabihf/bin/ld: cannot find crti.o: No such file or directory

https://travis-ci.org/MarcoFalke/secp256k1/jobs/624276878#L396

[real-or-random]

Ah yes, thanks for clarifying!