Re: [PATCH] Fix initramfs size calculation

Michael Holzheu
2010-08-26T08:55:55Z

Hello Sam,

On Wed, 2010-08-25 at 21:56 +0200, Sam Ravnborg wrote:
> On Wed, Aug 25, 2010 at 09:15:32PM +0200, Hendrik Brueckner wrote:
> > Sam,
> >
> > I have work together with Michael on this patch... see my comments below
> >
> > On Wed, Aug 25, 2010 at 08:06:01PM +0200, Sam Ravnborg wrote:
> > > On Wed, Aug 25, 2010 at 05:57:12PM +0200, Michael Holzheu wrote:
> > >
> > > Another way to fix this could be to align . to an even
> > > address like this:
> > > > #define INIT_RAM_FS \
> > > > . = ALIGN(PAGE_SIZE); \
> > > > VMLINUX_SYMBOL(__initramfs_start) = .; \
> > > > *(.init.ramfs) \
> > > . = ALIGN(32); \
> > > > VMLINUX_SYMBOL(__initramfs_end) = .;
> > > >
> > >
> > > 32 was selected as this is what we will introduce as the default
> > > alignment in linker scripts anyway.
> > >
> > > This I guess is a problem we have had some time and a minimal fix is
> > > easier to have backported by the stable team.
> >
> > The first thought was similar but using ALIGN(2). However, the current
> > implementation of populate_rootfs() passes the calculated size to the
> > decompress functions. If __initramfs_end is aligned, the resulting size
> > might be greater than the real size of the initramfs.
> > So I guess this might also cause problems.
> Another variant could be to explicit add alignment in the .S files
> so the section is always aligned to a even byte boundary (or maybe 32 byte boundary).

Then still the unpack_to_rootfs() function will not get the correct size
of the compressed file, because "__initramfs_end - __initramfs_start"
can be bigger than the real file size depending on the used the
alignment. I would assume that not all decompression functions will
work, if a bigger value is passed to decompress_method().

Michael