linux-kernel - Re: [PATCH] Makefile: LTO: have linker check -Wframe-larger-than

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Date:   Mon, 24 May 2021 15:29:18 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Masahiro Yamada <masahiroy@...nel.org>
Cc:     Kees Cook <keescook@...omium.org>,
        clang-built-linux@...glegroups.com,
        Candle Sun <candlesea@...il.com>, linux-kbuild@...r.kernel.org,
        Fangrui Song <maskray@...gle.com>,
        linux-kernel@...r.kernel.org,
        Michal Marek <michal.lkml@...kovi.net>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Nathan Chancellor <nathan@...nel.org>
Subject: Re: [PATCH] Makefile: LTO: have linker check -Wframe-larger-than

On Thu, 11 Mar 2021 17:09:41 -0800, Nick Desaulniers wrote:
> -Wframe-larger-than= requires stack frame information, which the
> frontend cannot provide. This diagnostic is emitted late during
> compilation once stack frame size is available.
> 
> When building with LTO, the frontend simply lowers C to LLVM IR and does
> not have stack frame information, so it cannot emit this diagnostic.
> When the linker drives LTO, it restarts optimizations and lowers LLVM IR
> to object code. At that point, it has stack frame information but
> doesn't know to check for a specific max stack frame size.
> 
> [...]

Applied to for-linus/clang/features, thanks! This should be in -next
tomorrow and I'll send it on for -rc4 at the end of the week.

[1/1] Makefile: LTO: have linker check -Wframe-larger-than
      https://git.kernel.org/kees/c/24845dcb170e

-- 
Kees Cook