Date: Sat, 17 Mar 2018 02:49:27 +0100 From: Miguel Ojeda <miguel.ojeda.sandonis@...il.com> To: Linus Torvalds <torvalds@...ux-foundation.org> Cc: Al Viro <viro@...iv.linux.org.uk>, Florian Weimer <fweimer@...hat.com>, Kees Cook <keescook@...omium.org>, Andrew Morton <akpm@...ux-foundation.org>, Josh Poimboeuf <jpoimboe@...hat.com>, Rasmus Villemoes <linux@...musvillemoes.dk>, Randy Dunlap <rdunlap@...radead.org>, Ingo Molnar <mingo@...nel.org>, David Laight <David.Laight@...lab.com>, Ian Abbott <abbotti@....co.uk>, linux-input <linux-input@...r.kernel.org>, linux-btrfs <linux-btrfs@...r.kernel.org>, Network Development <netdev@...r.kernel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Kernel Hardening <kernel-hardening@...ts.openwall.com> Subject: Re: [PATCH v5 0/2] Remove false-positive VLAs when using max() On Fri, Mar 16, 2018 at 9:14 PM, Linus Torvalds <torvalds@...ux-foundation.org> wrote: > On Fri, Mar 16, 2018 at 1:03 PM, Miguel Ojeda > <miguel.ojeda.sandonis@...il.com> wrote: >>> >>> Kees - is there some online "gcc-4.4 checker" somewhere? This does >>> seem to work with my gcc. I actually tested some of those files you >>> pointed at now. >> >> I use this one: >> >> https://godbolt.org/ > > Well, my *test* code works on that one and -Wvla -Werror. > > It does not work with gcc-4.1.x, but works with gcc-4.4.x. > > I can't seem to see the errors any way, I wonder if > __builtin_choose_expr() simply didn't exist back then. > > Odd that you can't view warnings/errors with it. > > But it's possible that it fails on more complex stuff in the kernel. > > I've done a "allmodconfig" build with that patch, and the only issue > it found was that (real) type issue in tpm_tis_core.h. Just tested your max() with a Python script I wrote yesterday to try a lot of combinations for this thing. Your version gives some warnings in some cases, like: warning: signed and unsigned type in conditional expression [-Wsign-compare] #define __cmp(a,b,op) ((a)op(b)?(a):(b)) warning: comparison between signed and unsigned integer expressions [-Wsign-compare] #define const_max(a,b) __careful_cmp(a,b,>) warning: comparison of distinct pointer types lacks a cast (!!(sizeof((typeof(a)*)1==(typeof(b)*)1))) But it fails on something like (with warnings): int a[const_max(-30, 60u)]; Sorry... :-( Has anyone taken a look at the last one I sent? Patch attached with the draft changes on the kernel. It compiles fine the cases Kees cleaned up in the other patch, but also works without a explicit type, for mixed types, and for both positive and negative values. Cheers, Miguel View attachment "patch.diff" of type "text/x-patch" (2260 bytes)
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