[Mono-dev] Question on PPC and porting..

Randall Stewart rrs at lakerest.net
Sun Apr 26 10:58:21 EDT 2009

Hi all:

I am new to the list and am currently working on getting mono
to work with AIX (5.3 initially and then later 6.1) ;-)

I have been examining the ppc register storing routines and I find
in apple (ppc) the following from a simple call:

0x1edc <foo>:	mflr    r0
0x1ee0 <foo+4>:	stmw    r30,-8(r1)
0x1ee4 <foo+8>:	stw     r0,8(r1)
0x1ee8 <foo+12>:	stwu    r1,-96(r1)
0x1eec <foo+16>:	mr      r30,r1
0x1ef0 <foo+20>:	stw     r3,120(r30)
0x1ef4 <foo+24>:	stw     r4,124(r30)
0x1ef8 <foo+28>:	stw     r5,128(r30)
0x1efc <foo+32>:	stw     r6,132(r30)
0x1f00 <foo+36>:	lwz     r3,120(r30)
0x1f04 <foo+40>:	lwz     r4,124(r30)
0x1f08 <foo+44>:	lwz     r5,128(r30)
0x1f0c <foo+48>:	lwz     r6,132(r30)
0x1f10 <foo+52>:	bl      0x1e14 <fee>
0x1f14 <foo+56>:	mr      r0,r3
0x1f18 <foo+60>:	stw     r0,56(r30)
0x1f1c <foo+64>:	lwz     r0,56(r30)
0x1f20 <foo+68>:	mr      r3,r0
0x1f24 <foo+72>:	lwz     r1,0(r1)
0x1f28 <foo+76>:	lwz     r0,8(r1)
0x1f2c <foo+80>:	mtlr    r0
0x1f30 <foo+84>:	lmw     r30,-8(r1)
0x1f34 <foo+88>:	blr

Now I am trying to make sure my call chain offsets and such
are correct... the sp+8 is correct i.e. in arch/tramp.c
matches the apple type.

I also note that they are using r30 as the index to
the stack.. where as r31 is used in xlc (and gcc too in aix).
Now what makes me puzzled is the offset to stack_param's
For apple its defined as 24. Now this sort of matches what
is happening here.. its storing the registers at +24 to the
OLD stack... not the new one. i.e. 96+24 = 120.

This is also what happens in the xlc assembly as well. It appears
that each function locally allocates storage for its callers (not  
to use. When a function needs to use registers it stores
the old value in the function's callers stack NOT any locally
allocated stack.

Where as it appears the emit_save_parameters() routine is just
taking that offset for the emission of parameters... i.e. it
stores the registers in its allocated stack. This seems to me
that if a regular library function was being called that library
function would then overwrite those saved values.

Now either I am mis-reading the code, or maybe the assembly (I am a
bit rusty on ppc assembly). If someone could point out what I
am mis-reading I would appreciate it.

Any help would be appreciated...


Randall Stewart
803-317-4952 (cell)

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