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Re: [PATCH 0/3] aarch64: Update for vector abi

On 02/08/18 14:17, Carlos O'Donell wrote:
On 08/02/2018 06:44 AM, Szabolcs Nagy wrote:
ok (ld audit is another reason to avoid plt for vector functions..)

If you avoid the PLT with no way to add back a call through the PLT
this completely breaks developer tooling that uses the PLT, like
LD_AUDIT, latrace, and custom tooling. Be aware that there are large
customers in various industry verticals that use LD_AUDIT extensively.

it seems x86_64 also broke the 'plt entry abi' several times
(whenever new vector extensions were introduced)

we can do the same on aarch64, but that means plt entry does
not have a stable abi (new extensions don't work on old glibc)

in case of sve, supporting the plt entry has significant costs.
(stack usage, linux optimizations, save/restore overhead)
so i would like to avoid that.

it may be possible to keep the plt (and make ld_audit work),
but force bind now semantics for vector functions somehow, so
at least the lazy binding entry point remains backward compatible
and efficient.  but i'm not sure if the compiler can do this.

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