Messages in this thread | | | Subject | Re: linux-next: Tree for Aug 20 (Wno-alloc-size-larger-than) | From | Randy Dunlap <> | Date | Wed, 25 Aug 2021 22:10:24 -0700 |
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On 8/25/21 8:54 PM, Kees Cook wrote: > On Wed, Aug 25, 2021 at 10:49:19AM -0700, Randy Dunlap wrote: >> On 8/25/21 10:04 AM, Kees Cook wrote: >>> On Tue, Aug 24, 2021 at 11:58:59AM +1000, Stephen Rothwell wrote: >>>> On Mon, 23 Aug 2021 18:24:44 -0700 Randy Dunlap <rdunlap@infradead.org> wrote: >>>>> >>>>> This is just weird. What I am seeing is that for every source file >>>>> where gcc emits a warning: it then follows that up with this >>>>>>> cc1: warning: unrecognized command line option '-Wno-alloc-size-larger-than' >>>> >>>> I see the same, as well as: >>>> >>>> <stdin>:1515:2: warning: #warning syscall clone3 not implemented [-Wcpp] >>>> cc1: warning: unrecognized command line option '-Wno-alloc-size-larger-than' >>>> >>>> But only on my gcc 7.3.1 builds (the rest are gcc 10). >>>> >>>>> Smells like a gcc bug to me. >>>> >>>> Yes >>>> >>>> Also noted here: https://github.com/DynamoRIO/drmemory/issues/2099 (second comment) >>> >>> Okay, I think this work-around should work. I've been able to reproduce >>> the weird conditions, and this seems to behave correctly. Andrew, can >>> you fixup the fixup with this? >>> >>> >>> diff --git a/Makefile b/Makefile >>> index 26640899e7ca..c1842014a5de 100644 >>> --- a/Makefile >>> +++ b/Makefile >>> @@ -1094,8 +1094,13 @@ endif >>> ifdef CONFIG_CC_IS_GCC >>> # The allocators already balk at large sizes, so silence the compiler >>> -# warnings for bounds checks involving those possible values. >>> -KBUILD_CFLAGS += $(call cc-option, -Wno-alloc-size-larger-than) >>> +# warnings for bounds checks involving those possible values. While >>> +# -Wno-alloc-size-larger-than would normally be used here, some versions >>> +# of gcc (<9.1) weirdly don't handle the option correctly when _other_ >>> +# warnings are produced (?!), so instead use SIZE_MAX to effectively >>> +# disable it. >>> +# https://lore.kernel.org/lkml/20210824115859.187f272f@canb.auug.org.au >>> +KBUILD_CFLAGS += $(call cc-option, -Walloc-size-larger-than=SIZE_MAX) >>> endif >>> # disable invalid "can't wrap" optimizations for signed / pointers >>> >> >> Hi Kees, >> >> I get a lot of these: >> >> ../include/linux/slab.h: In function ‘keyctl_instantiate_key_common’: >> cc1: warning: invalid argument ‘SIZE_MAX’ to ‘-Walloc-size-larger-than=’ > > O_o > > I love how the documentation on this option is consistently wrong. :) > > I haven't been able to exactly reproduce this error on godbolt.org, but > I got close with trunk GCC: > gcc: error: argument to '-Walloc-size-larger-than=' should be a non-negative integer optionally followed by a size unit > > Even though stdint.h is included. :( > > Okay. How about _this_ fix? > > diff --git a/Makefile b/Makefile > index efa9bd36b158..141a851930e6 100644 > --- a/Makefile > +++ b/Makefile > @@ -1096,8 +1096,17 @@ endif > > ifdef CONFIG_CC_IS_GCC > # The allocators already balk at large sizes, so silence the compiler > -# warnings for bounds checks involving those possible values. > -KBUILD_CFLAGS += $(call cc-option, -Wno-alloc-size-larger-than) > +# warnings for bounds checks involving those possible values. While > +# -Wno-alloc-size-larger-than would normally be used here, earlier versions > +# of gcc (<9.1) weirdly don't handle the option correctly when _other_ > +# warnings are produced (?!). Using -Walloc-size-larger-than=SIZE_MAX > +# doesn't work (as it is documented to), silently resolving to "0" prior to > +# version 9.1 (and producing an error more recently). Numeric values larger > +# than PTRDIFF_MAX also don't work prior to version 9.1, which are silently > +# ignored, continuing to default to PTRDIFF_MAX. So, left with no other > +# choice, we must perform a versioned check to disable this warning. > +# https://lore.kernel.org/lkml/20210824115859.187f272f@canb.auug.org.au > +KBUILD_CFLAGS += $(call cc-ifversion, -ge, 0901, -Wno-alloc-size-larger-than) > endif > > # disable invalid "can't wrap" optimizations for signed / pointers
Yes, this works for me. Thanks.
Tested-by: Randy Dunlap <rdunlap@infradead.org>
-- ~Randy
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