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@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxx > > +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@xxxxxxxxxxxxxxxx +KBUILD_CFLAGS += $(call cc-ifversion, -ge, 0901, -Wno-alloc-size-larger-than) endif # disable invalid "can't wrap" optimizations for signed / pointers -- Kees Cook
