linux-kernel - Re: "interesting" entry in hibernation code was Re: [lkp-robot] [x86/asm] 51bad67ffb: int3:#[##]

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Message-ID: <6938886.d705BbSbgG@aspire.rjw.lan>
Date:   Sat, 19 May 2018 10:35:27 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Pavel Machek <pavel@....cz>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Peter Anvin <h.peter.anvin@...el.com>,
        kernel test robot <xiaolong.ye@...el.com>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrew Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Brian Gerst <brgerst@...il.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Peter Anvin <hpa@...or.com>, tipbuild@...or.com,
        LKP <lkp@...org>
Subject: Re: "interesting" entry in hibernation code was Re: [lkp-robot] [x86/asm] 51bad67ffb: int3:#[##]

On Saturday, May 19, 2018 9:00:08 AM CEST Pavel Machek wrote:
> Hi!
> 
> > Side note: doing some grepping, I find some other sequences that are a bit
> > scary, like this:
> > 
> > arch/x86/kernel/acpi/wakeup_32.S-.data
> > arch/x86/kernel/acpi/wakeup_32.S-ALIGN
> > arch/x86/kernel/acpi/wakeup_32.S:ENTRY(saved_magic)     .long   0
> > arch/x86/kernel/acpi/wakeup_32.S:ENTRY(saved_eip)       .long   0
> > 
> > so apparently people are using ENTRY() for data too (the same pattern
> > exists in wakeup_64.S).
> > 
> > So we end up having those odd 0x90 bytes (now 0xcc) in the data section as
> > "padding" between those two values. Crazy.
> 
> Sorry about that. I'm pretty sure intention was simply to use the
> variable from C code.. and ENTRY() worked. I was not aware that it has
> side effect of padding...
> 
> Let me see how this can be improved... (untested).
> 
> diff --git a/arch/x86/kernel/acpi/wakeup_32.S b/arch/x86/kernel/acpi/wakeup_32.S
> index 0c26b1b..d6f477f 100644
> --- a/arch/x86/kernel/acpi/wakeup_32.S
> +++ b/arch/x86/kernel/acpi/wakeup_32.S
> @@ -89,8 +89,8 @@ ret_point:
>  
>  .data
>  ALIGN
> -ENTRY(saved_magic)	.long	0
> -ENTRY(saved_eip)	.long	0
> +GLOBAL(saved_magic)	.long	0
> +saved_eip:	.long	0
>  
>  # saved registers
>  saved_idt:	.long	0,0

The Jiri Slaby's annotation patches touch this:

https://patchwork.kernel.org/patch/10409073/

Thanks,
Rafael