Messages in this thread | ![/](/images/icornerl.gif) | | From | Linus Torvalds <> | Date | Thu, 29 Aug 2019 15:26:30 -0700 | Subject | Re: objtool warning "uses BP as a scratch register" with clang-9 |
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On Thu, Aug 29, 2019 at 1:22 PM Arnd Bergmann <arnd@arndb.de> wrote: > > Maybe we can just pass -fno-builtin-memcpy -fno-builtin-memset > for clang when CONFIG_KASAN is set and hope for the best?
I really hate how that disables conversions both ways, which is kind of pointless and wrong. It's really just "we don't want surprising memcpy calls for single writes".
Disabling all the *good* "optimize memset/memcpy" cases is really sad.
We actually have a lot of small structures in the kernel on purpose (often for type safety), and I bet we use memcpy on them on purpose at times. I'd hate to see that become a function call rather than "copy two words by hand".
Even for KASAN.
And I guess that when the compiler sees 20+ "set to zero" it's quite reasonable to say "just turn it into a memset".
So maybe the right thing to do is to just special-case this code, and hope for the best. If moving the sas_ss_reset() out of the try/catch thing works, then by all means lets just do that.
(Partly because I've actually wanted to turn the try/catchj thing into a _real_ try/catch, not a "fall through and check at the end" like it just happens to be now - the try/catch is actually very misleading as it is now. So if this is the only case that matters, then...).
Linus
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