CodeWarrior's inline assembler and the Mach-O PIC base

Thread view:

Enable EMail Alerts

Start New Thread

Thread rating:

Mars Saxman - 23 Aug 2004 19:35 GMT

I am trying to modify an existing PEF-based threads library to work
under Mach-O. One critical function must be written in assembly
language, cannot use a conventional stack frame (it uses the nofralloc
directive), cannot modify any nonvolatile registers, and must load &
store the contents of two static variables.

I have updated the code that refers to static variables as follows:

#if EXE_FORMAT_MACHO
addis r4, r2, ha16(sCurrentThread) // r2 == rPIC
lwz r4, lo16(sCurrentThread)(r4)
#else
lwz r4, sCurrentThread
#endif

Now I need to load the PIC base into r2. The instruction sequence is
simple enough:

bl next
next:
mflr r2

Here's the hangup: how do I tell CodeWarrior's linker that the label
'next' represents the PIC base, and that it should calculate my static
data references relative to that point? I have not found any special
name or assembler directive that does the trick.

Mars Saxman
REAL Software

Reply to this Message

MW Ron - 30 Aug 2004 20:26 GMT

>I am trying to modify an existing PEF-based threads library to work
>under Mach-O. One critical function must be written in assembly
[quoted text clipped - 22 lines]
>data references relative to that point? I have not found any special
>name or assembler directive that does the trick.

Hi,

Sorry for the delay in replying. I was hoping someone could help, but
when no one did I asked one of our PowerPC engineers... he said.

I generally look to the runtime libraries for examples, in this case
there is an assembler directive: picbase which associates a picbase
register with it's label:

runtime.c: __cvt_fp2unsigned()

asm unsigned long __cvt_fp2unsigned(register double d)
{
#if __MACH__
mflr r0
bcl 20,31,@1
@1 mflr r4
picbase r4,@1

addis r4,r4,ha16(__constants)
la r4,lo16(__constants)(r4)
// restore the link register (I moved down here as scheduling)
mtlr r0
#else
entry __uitrunc
lwz r4,__constants(RTOC)
#endif

It is important to use "bcl 30,31,@1" to avoid link register stack
delays which happen when using "bl" to compute the address of the next
instruction (code will run correctly but might be slower).

again my apology for the delay.

Ron

Signature

Metrowerks Community Forum is a free online resource for developers
to discuss CodeWarrior topics with other users and Metrowerks' staff
-- http://www.metrowerks.com/community --

Ron Liechty - MWRon@metrowerks.com - http://www.metrowerks.com

Reply to this Message

Mac Forum / Programming / CodeWarrior / August 2004

CodeWarrior's inline assembler and the Mach-O PIC base