On Wed, Jun 10, 2015 at 03:08:14PM +0200, Andi Kleen wrote: > > > 2. Each callable function must never leave its own bounds (i.e. with a > > jump to outside the function) except when returning. > > That prevents a lot of optimizations with out of line code.
In most cases there are ways to keep the optimizations. For example: - grow the function bounds to keep the jump internal - duplicate the destination code inside the function - convert the jump to a call Also note that these rules only affect _callable_ functions, so the entry code and other non-function asm code can still be a pile of spaghetti (though I think Andy is working on improving that). > In fact even gcc with the right options can generate code that violates > this. Standard Linux constructions, such as exception handling, > also violate this. > > If your tool needs that your tool is broken. This tool only validates asm code, so I don't see how whatever gcc does is relevant. > BTW any other frame pointer requirement should be also optional, > as it slows down a number of CPUs, such as Atoms. Yes. This patch set is a first step towards being able to disable frame pointers. Once all callable functions are reasonably structured, we can start generating and validating DWARF CFI data. Then we can make a reliable DWARF unwinder and get rid of frame pointers. -- Josh -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
