Re: [RFA] Fix float argument passing in inferior function calls for ppc64

Thiago Jung Bauermann
2008-01-15T20:34:22Z

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On Tue, 2008-01-15 at 15:39 -0200, Thiago Jung Bauermann wrote:
> > Is the first word used for anything in the new ABI? If not, you could
> > support both ABIs by copying the value into both the first and the
> > second word.
>
> Great idea. I will resend the patch using that approach then.

What about this patch?

> > > I didn't touch the code which writes the float to a general register in
> > > the first word because I'm not sure how to test it. It is probably
> > > related to soft-float, I guess.
> >
> > Actually, it may be related to varargs. Or perhaps it is a leftover
> > from the 32-bit ABI code that was copied.
>
> I'll play with varargs and see if I can trigger that code and create a
> test for it.

I tried it, but turns out it's not possible to pass a 32-bit float to a
variadic function, you need to explicitly promote it to double first. So
if that if code writing to a general register is not used by soft-float,
then it may be dead code as you suggested.
--
[]'s
Thiago Jung Bauermann
Software Engineer
IBM Linux Technology Center

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2008-01-15 Thiago Jung Bauermann <bauerman@br.ibm.com>

* ppc-sysv-tdep.c (ppc64_sysv_abi_push_dummy_call): Write 32-bit
float in both first and second word in the doubleword, to support
old and new ABIs.

diff --git a/gdb/ppc-sysv-tdep.c b/gdb/ppc-sysv-tdep.c
index c2952f5..466b37f 100644
--- a/gdb/ppc-sysv-tdep.c
+++ b/gdb/ppc-sysv-tdep.c
@@ -829,6 +829,7 @@ ppc64_sysv_abi_push_dummy_call (struct gdbarch *gdbarch, struct value *function,
struct value *arg = args[argno];
struct type *type = check_typedef (value_type (arg));
const bfd_byte *val = value_contents (arg);
+
if (TYPE_CODE (type) == TYPE_CODE_FLT && TYPE_LENGTH (type) <= 8)
{
/* Floats and Doubles go in f1 .. f13. They also
@@ -836,40 +837,53 @@ ppc64_sysv_abi_push_dummy_call (struct gdbarch *gdbarch, struct value *function,
memory. */
if (write_pass)
{
+ gdb_byte regval[MAX_REGISTER_SIZE];
+ const gdb_byte *p;
+
+ /* Version 1.7 of the 64-bit PowerPC ELF ABI says:
+
+ "Single precision floating point values are mapped to
+ the first word in a single doubleword."
+
+ And version 1.9 says:
+
+ "Single precision floating point values are mapped to
+ the second word in a single doubleword."
+
+ GDB then writes single precision floating point values
+ at both words in a doubleword, to support both ABIs. */
+ if (TYPE_LENGTH (type) == 4)
+ {
+ memcpy (regval, val, 4);
+ memcpy (regval + 4, val, 4);
+ p = regval;
+ }
+ else
+ p = val;
+
+ /* Write value in the stack's parameter save area. */
+ write_memory (gparam, p, 8);
+
if (freg <= 13)
{
- gdb_byte regval[MAX_REGISTER_SIZE];
struct type *regtype
= register_type (gdbarch, tdep->ppc_fp0_regnum);
+
convert_typed_floating (val, type, regval, regtype);
regcache_cooked_write (regcache,
tdep->ppc_fp0_regnum + freg,
regval);
}
if (greg <= 10)
- {
- /* The ABI states "Single precision floating
- point values are mapped to the first word in
- a single doubleword" and "... floating point
- values mapped to the first eight doublewords
- of the parameter save area are also passed in
- general registers").
-
- This code interprets that to mean: store it,
- left aligned, in the general register. */
- gdb_byte regval[MAX_REGISTER_SIZE];
- memset (regval, 0, sizeof regval);
- memcpy (regval, val, TYPE_LENGTH (type));
- regcache_cooked_write (regcache,
- tdep->ppc_gp0_regnum + greg,
- regval);
- }
- write_memory (gparam, val, TYPE_LENGTH (type));
+ regcache_cooked_write (regcache,
+ tdep->ppc_gp0_regnum + greg,
+ regval);
}
- /* Always consume parameter stack space. */
+
freg++;
greg++;
- gparam = align_up (gparam + TYPE_LENGTH (type), tdep->wordsize);
+ /* Always consume parameter stack space. */
+ gparam = align_up (gparam + 8, tdep->wordsize);
}
else if (TYPE_CODE (type) == TYPE_CODE_FLT
&& TYPE_LENGTH (type) == 16