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x86_64 MULADDC assembly: add missing constraints about memory

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MULADDC_CORE reads from (%%rsi) and writes to (%%rdi). This fragment is
repeated up to 16 times, and %%rsi and %%rdi are s and d on entry
respectively. Hence the complete asm statement reads 16 64-bit words
from memory starting at s, and writes 16 64-bit words starting at d.

Without any declaration of modified memory, Clang 12 and Clang 13 generated
non-working code for mbedtls_mpi_mod_exp. The constraints make the unit
tests pass with Clang 12.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine
2021-09-14 00:13:05 +02:00
parent cacec723c8
commit d337fbc4cb
2 changed files with 6 additions and 3 deletions
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ChangeLog.d/muladdc-amd64-memory.txt Normal file
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Bugfix
* Fix missing constraints on x86_64 assembly code for bignum multiplication
that broke some bignum operations with (at least) Clang 12. Fixes #4786.