Messages in this thread | | | From | David Laight <> | Subject | RE: amusing SLUB compaction bug when CC_OPTIMIZE_FOR_SIZE | Date | Fri, 30 Sep 2022 21:34:23 +0000 |
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From: Hugh Dickins > Sent: 30 September 2022 17:22 > > On Fri, 30 Sep 2022, David Laight wrote: > > > > > Regarding "conflicting" alignment requests: yes, I agree with you, > > > > > it would have to be a toolchain bug if when asked to align 2 and to > > > > > align 4, it chose not to align 4. > > > > See https://godbolt.org/z/3nGsTaf5e > > the align() directive takes precedence. > > > > Here you only want to ensure the alignment is at least 4. > > Sorry, I don't understand the point you are making, > nor how to deduce it from the link which you give: > I'll leave it to those who understand better.
(I've copied Kees Cook - I think it is his patches that are increasing the function alignment. He'll need to find the thread history...)
IIRC -malign_functions is being used to put functions onto 16 byte boundaries to get aligned pad space before the function. Adding __align(4) overrides this and (I think) will remove the pad space.
I could only see the alignment directives in gcc ouput. clang didn't seem to generate them.
David
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