On 04/04/2013 10:42 AM, Jakub Jelinek wrote:
I think a similar optimization would be possible for access to
global variables because ld could compute the final layout of all
global variables in the binary itself, just as in the non-PIE case.
Nope. The thing is, depending on if the variable is known to bind locally
(for PIC that is essentially static or hidden visibility, for PIE you can
add to that global vars defined in the current CU), you either emit code
that avoids the indirection (say %rip addressing, GOTOFF etc.),
Even in PIE mode, it is possible to bind all global variables locally.
Even if the variable is defined in a DSO, we can allocate space for it
in the main program and arrange for the GOT indirection in the DSO to
point there. The DSO would use the indirection, but the main program
wouldn't.
It's slightly backwards, but isn't this how variables in DSOs are
referenced from position-dependent code?
--
Florian Weimer / Red Hat Product Security Team
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