Universal abi used in amm functions, no need for OS differentiation

[pittma]

During the review process, I mistakenly believed that the @_6_arg_universal_ABI did not account for Windows, as it conspicuously matches the Linux calling convention. Additionally, Windows does not have 6 registers in its calling convention, only 4—args 5 and 6 would be pushed onto the stack, so what I had here was wrong in two ways.

While debugging, I could see that this was segfaulting during a read of a pointer in %r11; this was what tipped me off.

Reading symbols from .\crypto\crypto_test.exe...
(gdb) run
Starting program: C:\Users\sdp\src\aws-lc\build\crypto\crypto_test.exe "--gtest_filter=BNTest.ModExp2TestVectors"
[New Thread 29840.0x700c]
[New Thread 29840.0x1b54]
[New Thread 29840.0x64b8]
Debugger detected. Disabling unwind tests.
Note: Google Test filter = BNTest.ModExp2TestVectors
[==========] Running 1 test from 1 test suite.
[----------] Global test environment set-up.
[----------] 1 test from BNTest
[ RUN      ] BNTest.ModExp2TestVectors
[New Thread 29840.0x64b4]

Thread 1 received signal SIGSEGV, Segmentation fault.
0x00007ff6cb416280 in L$loop5 ()
(gdb) disassemble 0x00007ff6cb416280
Dump of assembler code for function L$loop5:
=> 0x00007ff6cb416280 <+0>:     mov    (%r11),%r13

Running crypto_test was successful locally on:

Microsoft Windows Server
Version 21H2 (OS Build 20348.405)

On an SPR-based system. I have not tested this change on Linux locally yet, but I will in the next few hours.

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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.

[dkostic]

Hey Dan, thanks for looking into this! Could you please re-enable the code path (https://github.com/aws/aws-lc/blob/main/crypto/fipsmodule/cpucap/internal.h#L144) to test the change in the CI?

[pittma]

Hey Dan, thanks for looking into this! Could you please re-enable the code path (https://github.com/aws/aws-lc/blob/main/crypto/fipsmodule/cpucap/internal.h#L144) to test the change in the CI?

2e8d424 does include that change!

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.45%. Comparing base (c187579) to head (df392c3).
Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1869      +/-   ##
==========================================
- Coverage   78.46%   78.45%   -0.02%     
==========================================
  Files         585      585              
  Lines       99457    99459       +2     
  Branches    14237    14238       +1     
==========================================
- Hits        78042    78029      -13     
- Misses      20780    20795      +15     
  Partials      635      635              

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