9c: some binaries produce segmentation faults when compiled for ARMv7 with GCC on Linux

[9fans]

9c: some binaries produce segmentation faults when compiled for ARMv7 with GCC on Linux

[dancrossnyc]

So much has changed in the last three and a little-more than a half years, I'm going to close this. If it comes up again, please re-open.

[nsajko]

I think this is still an issue (but can not test it right now).

Context: ARM has multiple instruction sets (sometimes, even usually, supported by the same CPU): Thumb and Thumb2, "old" ARM (A32), and the 64-bit ARM A64. Certain special jump instructions are used for switching between them at run time. The "old" ARM (A32) instruction set is nowadays basically deprecated, for example the Cortex-M cores do not even support it.

The trouble is, as far as I understand, the libthread arm assembly is written so it would assemble to the "old" ARM (A32) instruction set, and GCC will compile C to Thumb and Thumb2 code.

The fix could maybe be making it known that the assembly-defined routines are A32, or to compile everything to A32, like aoeu did. But probably the better fix would be to assemble to the newer Thumb and Thumb2 instruction sets in the first place. This would require some changes to the simple assembly in libthread. Probably .syntax unified should be used.

Will investigate when I have more time.

[nsajko]

@aoeu If you are still interested please try master and my https://github.com/nsajko/plan9port/tree/assemblyTypeFunc regarding this issue. I expect master to still be broken for ARM, and my very simple fix to solve the issue.