Add msl to ARMConstantTweak and recognise ldrsw to prevent delocator errors

[jakemas]

Issues:

Resolves CI failures around delocator in #2175

Description of changes:

The FIPS static builds for ARM are failing CI:

[57%] Building ASM object crypto/fipsmodule/CMakeFiles/bcm_hashunset.dir/bcm-delocated.S.o
bcm.c: Assembler messages:
bcm.c:125130: Error: shift expression expected at operand 2 -- movi v4.4s,0xf,.Lbcm_redirector_msl,8' bcm.c:125133: Error: shift expression expected at operand 2 -- mvni v3.4s,0x1f,.Lbcm_redirector_msl,8'
bcm.c:130233: Error: shift expression expected at operand 2 -- movi v4.4s,0xf,.Lbcm_redirector_msl,8' bcm.c:130236: Error: shift expression expected at operand 2 -- mvni v3.4s,0x1f,.Lbcm_redirector_msl,8'
bcm.c:190061: Error: shift expression expected at operand 2 -- movi v4.4s,0xf,.Lbcm_redirector_msl,8' bcm.c:190064: Error: shift expression expected at operand 2 -- mvni v3.4s,0x1f,.Lbcm_redirector_msl,8'
bcm.c:206492: Error: shift expression expected at operand 2 -- movi v4.4s,0xf,.Lbcm_redirector_msl,8' bcm.c:206495: Error: shift expression expected at operand 2 -- mvni v3.4s,0x1f,.Lbcm_redirector_msl,8'

This was discussed back in #2096 but not merged due to the PR being closed.

The Arm instruction has a special argument msl (https://developer.arm.com/documentation/100069/0606/SIMD-Vector-Instructions/MOVI--vector-). The delocator is intepreting msl as a function (or global symbol). Since it’s not defined in the fipsmodule, it creates a jump function bcm_redirector_msl outside the fipsmodule that removes a potential relocation. The suffix of bcm_redirector_msl is the original token, which matches msl.

We fix by adding msl to the list of ARMConstantTweak and regenerate the delocate.peg.go file.

After testing this fix, I begin to see a second error in amazonlinux2023_clang15x_aarch_fips:

[339/575] Generating bcm-delocated.S
FAILED: crypto/fipsmodule/bcm-delocated.S /codebuild/output/src1965601223/src/github.com/aws/aws-lc/test_build_dir/crypto/fipsmodule/bcm-delocated.S 
panic: Symbol reference outside of ldr instruction [recovered]
    panic: error while processing "\tldrsw\tx9, [x9, :lo12:ml_dsa_zetas+4]\n" on line 120399: "Symbol reference outside of ldr instruction"

It seems that ldrsw is not recognised as ldr. We already have ldrsw in our code, so we extend the delocate.go to accept ldrsw in addition to ldr.

Call-outs:

Unblocks progress on work in the FIPS module, such as ED25519 and ML-DSA.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license and the ISC license.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.02%. Comparing base (9921cd9) to head (b289bd6).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2177   +/-   ##
=======================================
  Coverage   79.01%   79.02%           
=======================================
  Files         612      612           
  Lines      106071   106072    +1     
  Branches    14994    14994           
=======================================
+ Hits        83814    83821    +7     
+ Misses      21604    21598    -6     
  Partials      653      653           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[jakemas]

Confirmed on #2175 that these additions fix failing CI in c06dc55.

[andrewhop]

Please update the arm delocator tests to include msl and ldrsw.