freebsd-dev/gnu/usr.bin/as/README.pic

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A few short notes on PIC support.
. References to the symbol "_GLOBAL_OFFSET_TABLE_" are special. These always
PC relative to the start of the current instruction. Also, they occur
in "complex" expressions in function prologs, eg.
move _GLOBAL_OFFSET_TABLE_ + (. - L1 ), %some_register
The expression parser can't handle these generically, so the expression
above is recognised as a special case.
. Some archs have special PIC assembler syntax to reference static and global
data. This is handled in targ-cpu.c.
. Correct relocation_info must be output (eg. fields r_jmptable and r_baserel).
. Internal labels must be output in the symbol table if they are referred to
by PIC instructions. The linker must allocate a GOT slot for them.
. The former meaning of the -k switch ("WORKING_DOT" stuff), has been nuked
in favour of enabling PIC code recognition.
-pk