linux-kernel - Re: [PATCH] kbuild: correct size calculation of bzImgae / fix x86 boot

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Message-ID: <20091220130952.GD9719@1wt.eu>
Date:	Sun, 20 Dec 2009 14:09:52 +0100
From:	Willy Tarreau <w@....eu>
To:	Michael Tokarev <mjt@....msk.ru>
Cc:	Sam Ravnborg <sam@...nborg.org>, Michal Marek <mmarek@...e.cz>,
	Michael Guntsche <mike@...loops.com>,
	Oliver Hartkopp <oliver@...tkopp.net>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kbuild: correct size calculation of bzImgae / fix x86 boot

On Sun, Dec 20, 2009 at 01:47:13PM +0300, Michael Tokarev wrote:
> Willy Tarreau wrote:
> > On Sun, Dec 20, 2009 at 11:03:44AM +0100, Sam Ravnborg wrote:
> >> We use ... printf \x ... when calculating the size of the
> >> compressed kernel.
> >> Unfortunately dash built-in printf does not support this notation
> >> resulting in a non-bootable kernel.
> >>
> >> Fix this by always using the external version of printf.
> > 
> > Do we really want to workaround shells bugs ? I mean, either
> 
> There's no bugs in dash, as far as I can see.  According to
> POSIX, a) echo does not need to interpret _any_ escape sequences
> at all, and b) printf is not required to interpret \x sequences.

Interesting.

> Ref:
> 
> http://www.opengroup.org/onlinepubs/000095399/utilities/echo.html
> ...
>   string
>     A string to be written to standard output. If the first operand is -n,
>     or if any of the operands contain a backslash ( '\' ) character,
>    the results are implementation-defined.
> 
>     [XSI] On XSI-conformant systems, [..] the following character sequences
>     shall be recognized on XSI-conformant systems within any of the arguments:
> 
>     \a \b \c \f \n \r \t \v \\
>     \0num
>         Write an 8-bit value that is the zero, one, two, or three-digit octal
>         number num.
> 
> http://www.opengroup.org/onlinepubs/000095399/utilities/printf.html
> 
>  In addition to the escape sequences shown in the Base Definitions volume of IEEE
>  Std 1003.1-2001, Chapter 5, File Format Notation ( '\\', '\a', '\b', '\f', '\n',
>  '\r', '\t', '\v' ), "\ddd", where ddd is a one, two, or three-digit octal number,
>  shall be written as a byte with the numeric value specified by the octal number.

OK so the bug will not be fixed by calling /usr/bin/printf. It
will still work by pure luck when a the proper printf utility
will be there, but not when we use a posix-compliant one. The
proper fix then consists in writing octal chars in the form
of "\ddd" instead of "\xhh". And if dash is posix-compliant,
no need for the absolute path.

Willy

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