linux-kernel - RE: [RFC PATCH v2 2/2] objtool: fix x86 orc generation on big endian cross compiles

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Date:   Wed, 30 Sep 2020 13:06:27 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Vasily Gorbik' <gor@...ux.ibm.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>
CC:     Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "x86@...nel.org" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        "Miroslav Benes" <mbenes@...e.cz>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        Julien Thierry <jthierry@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [RFC PATCH v2 2/2] objtool: fix x86 orc generation on big endian
 cross compiles

From: Vasily Gorbik
> Sent: 30 September 2020 13:24
> 
> Correct objtool orc generation endianness problems to enable fully
> functional x86 cross compiles on big endian hardware.
> 
...
> +
> +#if defined(__BYTE_ORDER) ? __BYTE_ORDER == __LITTLE_ENDIAN : defined(__LITTLE_ENDIAN)
> +
>  struct orc_entry {
>  	s16		sp_offset;
>  	s16		bp_offset;
> @@ -57,6 +67,20 @@ struct orc_entry {
>  	unsigned	end:1;
>  } __packed;
> 
> +#else
> +
> +struct orc_entry {
> +	s16		sp_offset;
> +	s16		bp_offset;
> +	unsigned	bp_reg:4;
> +	unsigned	sp_reg:4;
> +	unsigned	unused:5;
> +	unsigned	end:1;
> +	unsigned	type:2;
> +} __packed;
> +
> +#endif

Shouldn't that be checking BITFIELD_ENDIAN.

I also think that (in the other patch) you can assume
that you don't need to byteswap if __KERNEL__ is defined.

	David

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