Re: Detect ARM MOVW/MOVT relocations in shared library links

[Daniel Jacobowitz <drow at false dot org>]

On Mon, Apr 27, 2009 at 10:06:39PM +0000, Joseph S. Myers wrote:
> ARMv7 has MOVW and MOVT instructions for loading constants without
> needing a constant pool, and associated relocations for when those
> constants are symbol addresses.
> 
> Of course PIC code can't use these instructions to load absolute
> symbol addresses.  This patch adds linker checks for linking objects
> using the relevant relocations into shared libraries, to detect the
> common mistake (for people coming from x86) of building objects
> without -fPIC and linking them into a shared library; the previous
> behavior was silently dropping the relocations and so generating a
> broken shared library, which is obviously undesirable.
> 
> Tested with no regressions with cross to arm-none-eabi.  OK to commit?
> 
> This certainly does not fix every case of ARM relocations that are
> either always unsafe for objects linked into shared libraries, or
> unsafe for such objects if the symbol referenced might not be resolved
> within the library at runtime; there are many other cases that may
> have similar issues, but these are the ones observed to cause problems
> in practice.  ("Unsafe" means not fully resolved at static link time
> and not converted to a dynamic relocation or no suitable dynamic
> relocation available to which to convert the relocation.)

This is OK, if it has survived a build of glibc.

-- 
Daniel Jacobowitz
CodeSourcery