[PATCH 3/3] ARM: zImage: fix issues with missing GOT entries for some global variables

[Nicolas Pitre]

On Wed, 20 Apr 2011, Shawn Guo wrote:

> On Wed, Apr 20, 2011 at 08:28:20AM -0400, Nicolas Pitre wrote:
> > On Wed, 20 Apr 2011, Uwe Kleine-König wrote:
> > 
> > > On Wed, Apr 20, 2011 at 12:15:04AM -0400, Nicolas Pitre wrote:
> > > > Many architecture specific versions of uncompress.h make use of global
> > > > variables marked static.  In such case the GOT is bypassed and the
> > > > code in head.S can't relocate them.
> > > > 
> > > > Instead of removing the static keyword from all those files and hope that
> > > > it won't come back, let's simply
> > > > define it out.
> > > > 
> > > > Signed-off-by: Nicolas Pitre <nicolas.pitre at linaro.org>
> > > > ---
> > > > 
> > > > This should fix remaining issues some people have with the DT append patch.
> > > > 
> > > >  arch/arm/boot/compressed/misc.c |   13 +++++++++++++
> > > >  1 files changed, 13 insertions(+), 0 deletions(-)
> > > > 
> > > > diff --git a/arch/arm/boot/compressed/misc.c b/arch/arm/boot/compressed/misc.c
> > > > index a565853..0125dae 100644
> > > > --- a/arch/arm/boot/compressed/misc.c
> > > > +++ b/arch/arm/boot/compressed/misc.c
> > > > @@ -30,7 +30,20 @@ unsigned int __machine_arch_type;
> > > >  static void putstr(const char *ptr);
> > > >  extern void error(char *x);
> > > >  
> > > > +/*
> > > > + * Many instances of mach/uncompress.h are including global variables.
> > > > + * Contrary to standard usage, we should _not_ mark those variables
> > > > + * static otherwise they get accessed via GOTOFF references which cannot
> > > > + * be modified at run time.  The entry code in head.S relies on the ability
> > > > + * to move writable sections around, and for that to work, we must have all
> > > > + * references going through the GOT which works only with non static
> > > > + * variables.  So, instead of asking for a non intuitive requirement
> > > > + * making many files non standard according to accepted coding practices
> > > > + * we fix the issue here by simply defining the static keyword to nothing.
> > > > + */
> > > > +#define static /* non-static */
> > > >  #include <mach/uncompress.h>
> > > > +#undef static
> > > This has a strange side effect, i.e. 
> > > 
> > > 	static something *ptr;
> > > 
> > > isn't initialised to NULL anymore IIRC. So the maintainers of
> > > the various mach/uncompress.h still need to be aware of the issue.
> > 
> > Please tell me more about your setup.  This should still be initialized 
> > to NULL.  If not then something else is still wrong.
> > 
> Though I'm unsure if it realistically exists, what if it's a static
> variable inside a function?  It's actually changing something, right?

Right.  In that case the variable is allocated to the .data section, but 
we explicitly discard .data at link time to prevent a successful build.


Nicolas