Ian Lance Taylor wrote:
This is talking about position independent code, which is not the same
as relocatable code. Relocatable code is code whose address may be
assigned at link time. Position independent code is code whose
address may be assigned at run time.
It is more understandable to think of that as load time, rather than run
time, and to think of it in terms of efficiency rather than absolute
can/can't.
Many kinds of relocation cannot be used in PIC code even though they can
be adjusted at load time. Other kinds of relocation can be used in PIC
code even though they require adjustments at load time.
All object files are relocatable. For most targets, only object files
compiled with -fpic or -fPIC or -pie are position independent.
On most platforms, few if any shared objects are truly position
independent. They need to be adjusted for position at load time.
-fPIC may make some constructs truly position independent, for which the
most efficient code would require link time adjustment.
-fPIC mainly clusters the load time adjustments together to reduce the
performance and security consequences of the load time adjustment
process, where the most efficient code would require link and/or load
time adjustments distributed through the code segment.
