Andrew Cagney wrote:

> Hello,
> 
> I'm trying to find a little history on the original ABI used by DEC on 
> the PMAX (little endian MIPS) machines.
> 
> I'm firstly wondering what the abi is correctly called.

COFF.

> Second, according to the ABI, how should small structs be passed vis:
> 
> struct c1 { char c; };
> void foo (struct c1 c1);

I don't have an ABI document, but both appear to be passed on the stack.
Here's the assembly output of the a simple C program (source included in
the asm- more assemblers should do this :-):

 .verstamp 3 0
 .extern c1 1
 .extern foo 1
 .text 
 .align 2
 .file 2 "foo.c"
 .globl main
 .loc 2 5
 #   1 struct c1 { char c; };
 #   2 struct foo { struct c1 c1 };
 #   3 
 #   4 main()
 #   5 {
 .ent main 2
main:
 .option O1
 subu $sp, 32
 sw $31, 28($sp)
 .mask 0x80000000, -4
 .frame $sp, 32, $31
 .loc 2 5
 .loc 2 9
 #   6  extern struct c1 c1;
 #   7  extern struct foo foo;
 #   8 
 #   9  bar1(c1);
 lbu $14, c1
 sb $14, 0($sp)
 lw $4, 0($sp)
 .livereg 0x0800000E,0x00000000
 jal bar1
 .loc 2 10
 #  10  bar2(foo);
 lbu $15, foo
 sb $15, 0($sp)
 lw $4, 0($sp)
 .livereg 0x0800000E,0x00000000
 jal bar2
 .loc 2 11
 #  11 }
 move $2, $0
 .livereg 0x2000FF0E,0x00000FFF
 lw $31, 28($sp)
 addu $sp, 32
 j $31
 .end main

Making the variables automatic just changes the "lbu" to references the
stack instead of external storage.

Simon.
--
Simon Burge                            <simonb@wasabisystems.com>
NetBSD CDs, Support and Service:    http://www.wasabisystems.com/