[Patch, Gas, AArch64][0/1] Fix diagnostics for exclusive load/stores and reclassify Armv8.7-A ST/LD64 Atomics.

[Tejas Belagod]

Hi,

Following upstream pointing out some inconsistencies in diagnostics,

https://sourceware.org/pipermail/binutils/2021-February/115356.html

attached is a patch set that fixes the issues. I believe a combination of two patches mainly contributed to these bugs:

https://sourceware.org/pipermail/binutils/2020-November/113961.html
https://sourceware.org/pipermail/binutils/2018-June/103322.html

A summary of what this patch set fixes:

For instructions

STXR w0,x2,[x0]
STLXR w0,x2,[x0]

The warning we emit currently is misleading:

t.s:9: Warning: unpredictable: identical transfer and status registers --`stlxr w0,x2,[x0]'
t.s:10: Warning: unpredictable: identical transfer and status registers --`stxr w0,x2,[x0]'

it ought to be:

t.s:9: Warning: unpredictable: identical base and status registers --`stlxr w0,x2,[x0]'
t.s:10: Warning: unpredictable: identical base and status registers --`stxr w0,x2,[x0]'

For instructions:
ldaxp x0,x0,[x0]
ldxp x0,x0,[x0]

The warning we emit is incorrect

t.s:11: Warning: unpredictable: identical transfer and status registers --`ldaxp x0,x0,[x0]'
t.s:12: Warning: unpredictable: identical transfer and status registers --`ldxp x0,x0,[x0]'

it ought to be:

Warning: unpredictable load of register pair -- `ldaxp x0,x0,[x0]'
Warning: unpredictable load of register pair -- `ldxp x0,x0,[x0]'

For instructions
        stlxp   w0, x2, x2, [x0]
        stxp    w0, x2, x2, [x0]

We don't emit any warning when it ought to be:

t.s:13: Warning: unpredictable: identical base and status registers --`stlxp w0,x2,x2,[x0]'
t.s:14: Warning: unpredictable: identical base and status registers --`stxp w0,x2,x2,[x0]'


For instructions:
        st64bv  x0, x2, [x0]
        st64bv  x2, x0, [x0]

We incorrectly warn when its not necessary. This is because we classify them incorrectly as ldstexcl when it should be lse_atomics in the opcode table. The incorrect classification makes it pick up the warnings from warning on exclusive load/stores.

Thanks,
Tejas.