Date: Tue, 27 Mar 2018 07:47:48 +0200 From: Ingo Molnar <mingo@...nel.org> To: Kees Cook <keescook@...omium.org> Cc: Andrew Morton <akpm@...ux-foundation.org>, Linus Torvalds <torvalds@...ux-foundation.org>, Martin Uecker <Martin.Uecker@....uni-goettingen.de>, Josh Poimboeuf <jpoimboe@...hat.com>, Rasmus Villemoes <linux@...musvillemoes.dk>, Randy Dunlap <rdunlap@...radead.org>, Miguel Ojeda <miguel.ojeda.sandonis@...il.com>, David Laight <David.Laight@...lab.com>, Ian Abbott <abbotti@....co.uk>, linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com Subject: Re: [PATCH v6] kernel.h: Retain constant expression output for max()/min() * Kees Cook <keescook@...omium.org> wrote: > In the effort to remove all VLAs from the kernel, it is desirable to > build with -Wvla. However, this warning is overly pessimistic, in that > it is only happy with stack array sizes that are declared as constant > expressions, and not constant values. One case of this is the evaluation > of the max() macro which, due to its construction, ends up converting > constant expression arguments into a constant value result. > > All attempts to rewrite this macro with __builtin_constant_p() failed with > older compilers (e.g. gcc 4.4). However, Martin Uecker constructed a > mind-shattering solution that works everywhere. Cthulhu fhtagn! > > This patch updates the min()/max() macros to evaluate to a constant > expression when called on constant expression arguments. This removes > several false-positive stack VLA warnings from an x86 allmodconfig > build when -Wvla is added: Cool! Acked-by: Ingo Molnar <mingo@...nel.org> How many warnings are left in an allmodconfig build? Thanks, Ingo
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