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Re: sse{2,3,4.2}, altivec, neon, ...




On Tue, Aug 08, 2017 at 04:47:26AM +0200, Adam Borowski wrote:
> On Sat, Aug 05, 2017 at 10:28:36PM +0200, Adam Borowski wrote:
> > It's easy to quite reliably detect the presence of such instructions
> > (probably no one JITs such code).  There's no real way to check if it's
> > executed unconditionally, though -- a lot of software has optimized code
> > paths that are chosen at runtime.
> > 
> > I guess we could apply such check to the archive: for example, if any of
> > these instructions are present in a code section: [snip]
> > then the program may need sse2.  But there's no good way to weed out false
> > positives automatically, so all we'd get is a list of candidates to check.
> 
> I went through the whole archive and disassembled all binaries in unstable
> in amd64 and i386 (not sure where to get a good list of neon instructions
> for armhf) -- results attached, and so is the script for analyzing a
> package[1].

Thanks, that's a really useful effort.

> Alas, there's way too many false positives to turn this into a lintian
> check.  There's 254 amd64 and 409 i386 sources which produce executables
> that include those instructions (I ignored other ISA extensions for now),
> most of them use proper runtime detection.  So unless someone can propose
> a better check, they'd need to be tested by hand.
>...

There are groups of packages (Go, gcl, haskell) that are either buggy 
due to one bug or can be whitelisted together.

The majority of packages in the amd64 list seem to be binaries built by Go.
I checked one case in a package, and that was code with proper runtime 
detection copied from golang-1.8 (Go doesn't have shared libraries).

Something like skipping binaries based on "objdump -t --section=.gosymtab" 
could whitelist these.

cu
Adrian

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed