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From: Sascha Hauer <s.hauer@pengutronix.de>
To: Trent Piepho <tpiepho@kymetacorp.com>
Cc: barebox <barebox@lists.infradead.org>
Subject: Re: [PATCH] ARM: Remove kernel booting call for thumb2 mode
Date: Fri, 4 Dec 2015 08:20:02 +0100	[thread overview]
Message-ID: <20151204072002.GU11966@pengutronix.de> (raw)
In-Reply-To: <1449105900.26955.1.camel@rtred1test09.kymeta.local>

On Thu, Dec 03, 2015 at 01:24:56AM +0000, Trent Piepho wrote:
> The asm code to do the actual call into the kernel (or another
> barebox) when compiled in thumb2 mode isn't necessary.  gcc generates
> a perfectly good calling sequence from a normal function pointer call.
> If it didn't, the code in bootstrap_boot() that uses a function
> pointer to jump to the 2nd stage barebox from an xloader wouldn't
> work.
> 
> It appears to be allowed that the call to kernel() could return, as
> neither start_linux() nor kernel() are marked noreturn, and there is
> code after calls to start_linux().
> 
> The asm code has a bug in this case, as it uses bx and not blx, and
> thus doesn't set the link register.  Since it's a tail call, this
> would be okay, but only if the LR value from the start of
> start_linux() (and the callee-saved registers) are restored
> beforehand, which isn't done.  The gcc generated call sequence will do
> this.

The kernel won't return, so this bug shouldn't hit us. Anyway, nice
cleanup. Tested and applied, thanks

Sascha


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      parent reply	other threads:[~2015-12-04  7:20 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-12-03  1:24 Trent Piepho
2015-12-04  2:28 ` Trent Piepho
2015-12-04  7:30   ` Sascha Hauer
2015-12-04 19:19     ` Trent Piepho
2015-12-04  7:20 ` Sascha Hauer [this message]

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