[Bf-committers] OpenMP issues with msvc2013 builds

[Martijn Berger]

On Wed, Aug 6, 2014 at 10:33 PM, Chad Fraleigh <chadf at triularity.org> wrote:

> It's not ideal, and would be coded to each specific vcompXXX.dll (and
> patched/updated versions).
>
> However, assuming the location of that flag is a fixed offset from the dll
> image, the general idea might be:
>
>  - Call GetModuleHandle() for each supported target (i.e. vcomp120.dll,
> vcomp120d.dll), until one is found.
>
>  - Calculate the address of the flag from the module base.
>
>  - Calculate the address of the code where it does the OMP_WAIT_POLICY
> active/passive checks and verify a few of the static opcode bytes (either
> verbatim, or with a checksum/hash).
>
We can most likely also just look at specific dll version and see if we
"know" it.

>
>  - Get the address that code references for the flag, and if it matches the
> earlier calculation, then consider it validated, and change the flag at
> that address.
>
>  - If no supported dll's were found, or couldn't be verified, output a
> warning to stderr about bad performance.
>

Looks good on paper. It is good to realize that we re-distribute vcomp and
thus have pretty good control over what version we use.
Main problem is that someone needs to actually try this by implementing it
:)


>
>
>
>  -Chad
>