Messages in this thread | | | From | Andy Lutomirski <> | Date | Thu, 7 May 2015 20:22:42 -0700 | Subject | Re: Avoiding unnecessary jump relocations in gas? |
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On Thu, May 7, 2015 at 9:21 AM, H.J. Lu <hjl.tools@gmail.com> wrote: > On Thu, May 7, 2015 at 4:52 AM, Jan Beulich <JBeulich@suse.com> wrote: >>>>> On 07.05.15 at 08:02, <luto@amacapital.net> wrote: >>> AFAICT gas will produce relocations for jumps to global labels in the >>> same file. This doesn't seem directly harmful to me, except that, on >>> x86, it forces five-byte jumps instead of two-byte jumps. >>> >>> This seems especially unfortunate, since even hidden and protected >>> symbols have this problem. >>> >>> Given that many users don't want interposition support (especially the >>> kernel and anyone using .hidden or .protected), it would be nice to >>> have a command-line option to turn this off and probably also to turn >>> it off by default for hidden and protected symbols. Can gas do this? >> >> I've been running with the below changes (taken off of a bigger set >> of changes, so the line numbers may look a little odd) for the last >> couple of years. I never tried to submit this change because so far >> I couldn't find the time to check whether this would have any >> unwanted side effects on cases I don't normally use. >> > > This is the patch I checked in. > > Thanks. > > -- > H.J. > --- > Branches to global non-weak symbols defined in the same segment with > non-default visibility can be optimized the same way as branches to > local symbols.
Would it make sense to also add a command line option along the lines of gcc's -fno-semantic-interposition or some way to override the default visibility? AFAICS this patch helps but only if asm code gets liberally sprinkled with .hidden or .protected directives.
--Andy
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