boot decompressor code error

[Uwe Kleine-König]

Hello Brian,

On Wed, Nov 03, 2010 at 09:16:12AM +0100, Brian Murphy wrote:
> On Fri, Oct 29, 2010 at 12:56 PM, Russell King - ARM Linux
> <linux at arm.linux.org.uk> wrote:
> > On Fri, Oct 29, 2010 at 12:22:47PM +0200, Brian Murphy wrote:
> >> Hi,
> >> There is a problem with the boot decompression code when the inflate
> >> method is used on arm.
> >> In fact two. The second of which is also a problem on all architectures.
> >> The first, and more serious, is that static local variables seem not
> >> to be supported,
> >
> > static local variables are no different from static global variables
> > except their scope.  static local variables can only be referenced
> > from within the block which they are defined and any child blocks,
> > whereas static global variables can be referenced by any code in the
> > same compilation unit.
> >
> > Their storage and initialization in both cases is identical.
> >
> >> this means that
> >> some tables initialized as static locals point to a place in ram where
> >> the tables are not.
> >> The function
> >>
> >> static void zlib_fixedtables(struct inflate_state *state)
> >>
> >> includes inffixed.h which contains two static tables and
> >
> > Both these tables are 'const' which means they end up in the read-only
> > section, and ultimately the text section of the image, not the data
> > section.
> >
> >> int zlib_inflate(z_streamp strm, int flush)
> >>
> >> contains a static local "order". The second seems not to have much
> >> influence on decompression
> >> but the first causes images (at least of a certain size) to fail
> >> decompression.
> >
> > Again, this is "static const unsigned short order[19] = ..." which
> > because of the const, ends up in the read-only section and therefore
> > the text section of the image.
> >
> > This is what I see from arm-linux-nm -n arch/arm/boot/compressed/vmlinux:
> > ...
> > 000835f0 t order.0
> > 00083618 t lenfix.1
> > 00083e18 t distfix.2
> > ...
> > which clearly shows these tables in the text section.  Also
> > arm-linux-objdump -t arch/arm/boot/compressed/decompress.o shows:
> > ...
> > 000000fc l     O .rodata        00000026 order.0
> > 00000124 l     O .rodata        00000800 lenfix.1
> > 00000924 l     O .rodata        00000080 distfix.2
> > ...
> > which shows that these were placed into the .rodata section initially,
> > as I explained above.
> >
> > Can you show your output from the above commands please?  Also show
> > the output of:
> >
> > arm-linux-nm -n arch/arm/boot/compressed/vmlinux|grep '\<__bss_start\>\|\<_end\>'
> >
> > arm-linux-objdump --section=.got -s arch/arm/boot/compressed/vmlinux
> >
> > Also, are you using ZBOOT_ROM=y or =n ?
> >
> 
> It looks like you were right, to some degree :). The table data is in
> the image transferred to
> the board but it looks like static locals are treated by the compiler
> as locals and allocated on
> the stack! This, of course, means that at some point they get
> (partially) overwritten by newer
> locals and thus corrupted.
Some time ago the decompressor was compiled using

	-Dstatic= 

Is this still the case for you?

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |