Re: -fPIC

Re: -fPIC

[Petter Wahlman]

hi!

position independent code (PIC) uses the ebx register to store the address of
the
global offset table (GOT), this register should thus be used with caution.
i belive you'r code references ebx with the "...: "b" (b).." expression.

shared libraries are genarally marginally slower than statically linked libs
because the linker has to dynamically evaluate procedure linkage table entries
(PLT),
and modify the global table offset's memory image accordingly (unless the
LD_BIND_NOW
environment variable is set).


regards

Petter Wahlman

-fPIC

[Rajrup Banerjee]

Hi,

Can I make out by just looking at a .o that it has been
compiled using -fPIC option?
Or else how can I differentiate between two binaries(.o) compiled
from the same source file, one with -fPIC option, and one
without it?

Many Thanks and Best Regards,
Rajrup.

Re: -fPIC

[Petter Wahlman]

hi!

position independent code (PIC) uses the ebx register to store the address of
the
global offset table (GOT), this register should thus be used with caution.
i belive you'r code references ebx with the "...: "b" (b).." expression.

shared libraries are genarally marginally slower than statically linked libs
because the linker has to dynamically evaluate procedure linkage table entries
(PLT),
and modify the global table offset's memory image accordingly (unless the
LD_BIND_NOW
environment variable is set).


regards

Petter Wahlman

-fPIC

[Jason Moxham]

Using gcc-2.95.3 under linux x86

writing a  C asm wrapper for the "cpuid" instruction

asm volatile("cpuid" : "+a" (a) 
		     : "b" (b) , "c" (c) , "d" (d) : "cc");

works

but if compiled for shared libary  ie with -fPIC
then you get an asm error saying that " bx is allready used"

even changing specific registers to "g" and putting extra "movl" asm
instructions doesnt help

Not yet tried this under gcc-3.0 

I heard that shared libs are slight slower than static libs ?
is this because an extra register is "used" ?

Jason Moxham
j.l.moxham@maths.soton.ac.uk