From: David Laight <David.Laight@ACULAB.COM>
To: 'Nick Desaulniers' <ndesaulniers@google.com>,
Masahiro Yamada <masahiroy@kernel.org>
Cc: Sami Tolvanen <samitolvanen@google.com>,
Candle Sun <candlesea@gmail.com>,
Fangrui Song <maskray@google.com>,
Michal Marek <michal.lkml@markovi.net>,
Nathan Chancellor <nathan@kernel.org>,
Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
clang-built-linux <clang-built-linux@googlegroups.com>
Subject: RE: [PATCH] Makefile: LTO: have linker check -Wframe-larger-than
Date: Mon, 15 Mar 2021 10:57:49 +0000 [thread overview]
Message-ID: <45f3e718a0c046f9a11f49eb199d425c@AcuMS.aculab.com> (raw)
In-Reply-To: <CAKwvOdnPhpKRs6SePCUCPs_2MUFbWgJiaf9F9J+aQZGESSQ9yA@mail.gmail.com>
From: Nick Desaulniers
> Sent: 12 March 2021 17:55
>
> On Thu, Mar 11, 2021 at 5:09 PM Nick Desaulniers
> <ndesaulniers@google.com> 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.
With LTO the linker ought to be able to do a stack frame check
across multiples functions in the call stack.
Clearly recursive calls cause issues.
Indirect ones as well - but does CFI include enough info
about what can be called from where to help?
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2021-03-15 10:58 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-12 1:09 [PATCH] Makefile: LTO: have linker check -Wframe-larger-than Nick Desaulniers
2021-03-12 17:55 ` Nick Desaulniers
2021-03-12 21:38 ` Nick Desaulniers
2021-03-15 10:57 ` David Laight [this message]
2021-05-24 22:29 ` Kees Cook
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