On Fri, Nov 17, 2017 at 12:21 AM, Alan Hayward <alan.hayw...@arm.com> wrote: > >> On 16 Nov 2017, at 19:32, Andrew Pinski <pins...@gmail.com> wrote: >> >> On Thu, Nov 16, 2017 at 4:35 AM, Alan Hayward <alan.hayw...@arm.com> wrote: >>> This final patch adds the clobber high expressions to tls_desc for aarch64. >>> It also adds three tests. >>> >>> In addition I also tested by taking the gcc torture test suite and making >>> all global variables __thread. Then emended the suite to compile with -fpic, >>> save the .s file and only for one given O level. >>> I ran this before and after the patch and compared the resulting .s files, >>> ensuring that there were no ASM changes. >>> I discarded the 10% of tests that failed to compile (due to the code in >>> the test now being invalid C). >>> I did this for O0,O2,O3 on both x86 and aarch64 and observed no difference >>> between ASM files before and after the patch. >> >> Isn't the ABI defined as non-clobbering the lower 64bits for normal >> function calls? Or is the TLS function "special" in that it >> saves/restores the 128bit registers; is that documented anywhere? The >> main reason why I am asking is because glibc is not the only libc out >> there and someone could have a slightly different ABI here. >> > > In NEON all the register SIMD registers are preserved around TLS calls - all > 128bits of each register. That’s standard ABI behaviour for NEON. > > SVE doesn’t have any explicit preserving of it’s SIMD registers. > > However, the NEON and SVE registers share the same silicon - the lower > 128bits of each SVE register is the same as the corresponding NEON > register. The side effect of this is that the lower 128bits of the SVE > registers > are getting backed up. > > Neither glibc or any libraries need updating to support this. > But, compilers do need to aware of this.
I had a different question. I asked if this specification of the TLS calls requiring not to clobber the lower 128bits of the SIMD registers documented anywhere. As I was trying to say I am in the middle of writing a libc and did not know of this requirement until I saw this thread. Thanks, Andrew > > > Alan.
