linux-kernel - Re: objtool warning "uses BP as a scratch register" with clang-9

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Date:   Tue, 27 Aug 2019 17:59:57 +0300
From:   Ilie Halip <ilie.halip@...il.com>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: Re: objtool warning "uses BP as a scratch register" with clang-9

> > $ clang-9 -c  crc32.i  -O2   ; objtool check  crc32.o
> > crc32.o: warning: objtool: fn1 uses BP as a scratch register

Yes, I see it too. https://godbolt.org/z/N56HW1

> Do you still see this warning with -fno-omit-frame-pointer (assuming
> clang has that option)?

Using this makes the warning go away. Running objtool with --no-fp
also gets rid of it.

I.H.