From mboxrd@z Thu Jan  1 00:00:00 1970
From: Russell King <rmk@ecs.soton.ac.uk>
To: egcs@cygnus.com
Subject: ARM Linux PIC implementation
Date: Tue, 02 Dec 1997 22:54:00 -0000
Message-id: <199712022300.XAA00810@raistlin.armlinux.org>
X-SW-Source: 1997-12/msg00149.html

Hi!

I'm working on GCC 2.7.2.2 trying to get an ARM PIC implementation going for
ARM/ELF.  I've managed to get some areas working, but unfortunately not others...

Currently, I have the following two problems:
1.  I need GCC to be able to output into the per-function constant pool
    an expression such as:
	.word	_GLOBAL_OFFSET_TABLE_ - L2 - 8
    This is not supported by the gcc 2.7.2.2 decode_rtx_const in varasm.c
    The RTX code that I'll be looking to call force_const_mem with is
    along the following lines:
	     (const (minus (minus (symbol ref "_GLOBAL_OFFSET_TABLE_)
				  (code label "L2"))
			   (const_int 8))

2.  For certain data types, I can't modify the GCC RTL to add in the PIC
    GOT register, eg

	extern int wibble;
	static char err_1[16][16] = { "Hello", "World" };
	static char *err_2[16] = {"Hello", "World" };
	char *p1, *p2;

	int foo (int c)
	{
        	wibble = c + c << 1;
	        p1 = err_1[c];
        	p2 = err_2[c];
	}

    The RTL looks good, except for the `p2 = err_2[c]' expression,
    and at no point do I see any call to the `movsi' op to indicate this -
    the only reference I see is a reference to LC4, the constant pool label
    which contains the `err_2' base address.

    The RTL generated by GCC is exactly the same as if it was not generating
    PIC therefore.  Is there somewhere else that I should be looking to add
    PIC functions?

I have added code for LEGITIMIZE_ADDRESS, LEGITIMATE_PIC_OPERAND_P,
FINALIZE_PIC, and added a new function to output a PIC address constant
(similar to output_addr_const.

Any suggestions that you have will be appreciated.  BTW, I'm not subscribed
to this mailing list, so if you could reply this mail please.
   _____
  |_____| ------------------------------------------------- ---+---+-
  |   |         Russell King        rmk@ecs.soton.ac.uk       --- ---
  | | | |     http://www.arm.uk.linux.org/~rmk/home.html     /  /  |
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  /   |               THE developer of ARM Linux              |+| /|\
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