Re: [rfa:ppc] Fix PPC/NBSD struct return; Was: userdef.exp regression for ppc?

[Jason R Thorpe <thorpej@wasabisystems.com>]

On Sat, Jun 01, 2002 at 01:21:52PM -0400, Andrew Cagney wrote:

 > Yep!  The attached fixes it.  Looks like PPC/NetBSD's custom GCC has a 
 > fixed struct return (I'm pretty sure that mainline GCC is broken).

Hmmmmm, both our 2.91 and 2.95 based compilers use:

#define RETURN_IN_MEMORY(TYPE)                                          \
  (TYPE_MODE (TYPE) == BLKmode                                          \
     && (DEFAULT_ABI != ABI_SOLARIS || int_size_in_bytes (TYPE) > 8))

...and don't override this anywhere.  The DEFAULT_ABI ends up as ABI_V4,
and not ABI_SOLARIS, so we definitely should be using the AIX structure
return convention there.

However, the following:

struct test_struct {
        int a;
        int b;
};

static struct test_struct test_struct = { 1,2 };

struct test_struct
test(void)
{

        return test_struct;
}

...does indeed produce code that appears to follow the SVR4 ABI rules:

        .file   "test.c"
gcc2_compiled.:
        .section        ".sdata","aw"
        .align 2
        .type    test_struct,@object
        .size    test_struct,8
test_struct:
        .long 1
        .long 2
        .section        ".text"
        .align 2
        .globl test
        .type    test,@function
test:
        lis 9,test_struct@ha
        la 9,test_struct@l(9)
        lwz 3,0(9)
        lwz 4,4(9)
        blr
.Lfe1:
        .size    test,.Lfe1-test
        .ident  "GCC: (GNU) 2.95.3 20010315 (release) (NetBSD nb1)"

...and adding another member to the structure (this making it > 8 bytes)
produces an in-memory return:

        .file   "test.c"
gcc2_compiled.:
        .section        ".data"
        .align 2
        .type    test_struct,@object
        .size    test_struct,12
test_struct:
        .long 1
        .long 2
        .space  4
        .section        ".text"
        .align 2
        .globl test
        .type    test,@function
test:
        lis 9,test_struct@ha
        la 11,test_struct@l(9)
        lwz 10,test_struct@l(9)
        lwz 8,8(11)
        lwz 0,4(11)
        stw 10,0(3)
        stw 0,4(3)
        stw 8,8(3)
        blr
.Lfe1:
        .size    test,.Lfe1-test
        .ident  "GCC: (GNU) 2.95.3 20010315 (release) (NetBSD nb1)"

AHA!  I see why.  In the 2.91 and 2.95 compilers, config/netbsd.h
defines DEFAULT_PCC_STRUCT_RETURN to 0, which causes GCC's
aggregate_value_p() to effecively give the SVR4 ABI semantics.

Yes, gcc 3.1 and gcc-current are definitely broken in this regard for
NetBSD, then (I haven't had a chance to do much gcc work on powerpc-netbsd,
but I'm obviously going to have to pay a bit more attention to it now).

I'll fix that up soon, and will simply remove the broken abi struct return
stuff from ppcnbsd-tdep.c.

-- 
        -- Jason R. Thorpe <thorpej@wasabisystems.com>