On Thu, May 28, 2015 at 08:29:31AM -0700, Richard Henderson wrote:
> On 05/28/2015 04:27 AM, H.J. Lu wrote:
> > You get consecutive jmpq's because x86 PLT entry is used as the
> > canonical function address. If you compile main with -fno-plt -fPIE, you
> > get:
>
> Well, duh. If the main executable has no PLTs, they aren't used as the
> canonical function address. Surely you aren't proposing that as a solution?
Why not? Is there a way we could prevent the main program from having
PLT even when it's non-PIE? Instead of:
call foo
the compiler could generate
call *foo@GOTABS_RELAXABLE
Then the linker would replace this with "call foo" if foo is defined
in the main program. For address loads, instead of:
mov $foo, %eax
or:
lea foo, %eax
you would have:
mov foo@GOTABS_RELAXABLE, %eax
and the linker could likewise relax this to an immediate mov. More
elaborate arithmetic on the function address might be hard to do in an
efficient but relaxable way; however, I don't think the compiler ever
needs to do that, and if it did, there would just be a few odd cases
that still generate PLT thunks.
Am I missing something?
Rich
