On 02/24/15 07:02, Daniel Sanders wrote: > Without this, a 'break' instruction is executed very early in the boot and > the boot hangs. > > The problem is that clang doesn't honour named registers on local variables > and silently treats them as normal uninitialized variables. However, it > does honour them on global variables. > > Signed-off-by: Daniel Sanders <daniel.sanders@xxxxxxxxxx> > Cc: Ralf Baechle <ralf@xxxxxxxxxxxxxx> > Cc: Paul Burton <paul.burton@xxxxxxxxxx> > Cc: Markos Chandras <markos.chandras@xxxxxxxxxx> > Cc: James Hogan <james.hogan@xxxxxxxxxx> > Cc: linux-mips@xxxxxxxxxxxxxx > Cc: Behan Webster <behanw@xxxxxxxxxxxxxxxxxx> > Cc: Sergei Shtylyov <sergei.shtylyov@xxxxxxxxxxxxxxxxxx> > Cc: David Daney <ddaney.cavm@xxxxxxxxx> > --- > v2 of this patch has been updated following David Daney's request to preserve > the name of the original named register local. > > v3 of this patch just rebases to master and adds some background discussion from > the previous threads. > > For reference, a similar patch for ARM's stack pointer has already been merged: > 0abc08b ARM: 8170/1: Add global named register current_stack_pointer for ARM > > LLVM is unlikely to support uninitialized reads of named register locals in the > foreseeable future. There are some significant implementation difficulties and > there were objections based on the future direction of LLVM. The thread is at > http://lists.cs.uiuc.edu/pipermail/llvmdev/2014-March/071555.html. I've linked > to the bit where the issues started to be discussed rather than the start of > the thread. > > Difficulty and objections aside, it's also a very large amount of work to > support a single (as far as I know) user of named register locals, especially > when the kernel has already accepted patches to switch named register locals to > named register globals in the arm and arm64/aarch64 arches. > > arch/mips/include/asm/thread_info.h | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/arch/mips/include/asm/thread_info.h b/arch/mips/include/asm/thread_info.h > index 55ed660..2f0dba3 100644 > --- a/arch/mips/include/asm/thread_info.h > +++ b/arch/mips/include/asm/thread_info.h > @@ -55,10 +55,10 @@ struct thread_info { > #define init_stack (init_thread_union.stack) > > /* How to get the thread information struct from C. */ > +register struct thread_info *__current_thread_info __asm__("$28"); > + > static inline struct thread_info *current_thread_info(void) > { > - register struct thread_info *__current_thread_info __asm__("$28"); > - > return __current_thread_info; > } > Acked-by: Behan Webster <behanw@xxxxxxxxxxxxxxxxxx> -- Behan Webster behanw@xxxxxxxxxxxxxxxxxx
