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enabling/disabling AltiVec in Firefox and derived browsers (ArcticFox)

On Monday, March 1, 2021, Riccardo Mottola <riccardo.mottola@libero.it> wrote:

> A quick solution would to have this configure as a convenience, but have a way to pass an --enable-altivec and -disable-altivec (or with/without?) parameter to configure.

EABI v2.0 rather unfortunately, despite it being optional in the OpenPOWER Compliancy Suite, made SIMD mandatory.

EABI v1.5 does not require SIMD.

the problem is that the assumption "#ifdef POWER9" is bleeding through to many code repositories.

Tulio Magno Quites Machado Filho is currently working on glibc6 patches which reverse these erroneous assumptions, replacing them with "#ifdef VSX" thus allowing people to compile code that does not rely on SIMD.

unfortunately it is somewhat a lost cause because of the mistake made in EABI v2.  modifying EABI v2 to make SIMD optional is no longer possible because it would break backwards compatibility, the only option being to create a new triplet, then an entire new distro port, and that is a 3 to 5 year process.

an alternative solution is to have a kernel-level emulator of SIMD instructions.

fascinatingly there is precedent for this in the form of sstep.c which triggers from illegal instruction trap and emulates some parts of the OpenPOWER ISA.


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