Info on PIC code

Doug Wyatt <>
10 Jun 1997 23:54:26 -0400

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From: Doug Wyatt <>
Newsgroups: comp.compilers
Date: 10 Jun 1997 23:54:26 -0400
Organization: MIT
Keywords: code, question, comment

Are there any good references on the specifics on PIC code
implementations? In particular, I'm interested in PIC from gcc in x86
machines. I need info such as persistency of the PIC register,
when/where PIC register values are calculated, offset formulas for
symbols at runtime, etc.

I am currently trying to build some shared libraries for an OS we are
developing and need to know what sort of register manipulations are
legal and where. I tried to munge through the source to gcc but that
was getting me nowhere.

Doug Wyatt
Lab for Computer Science
M.I.T. (617)-253-7436
[A quick look at the code suggests that it uses a procedure lookup table
and global offset table like the ones that Sun's shared libraries do, and
that %bx is reserved to hold the address of the PLT. I also note that on
my BSD/OS 2.1 box, the assembler can't assemble the compiler's output when
you tell it to generate PIC. -John]

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