[PATCH] Fix handling of uint32_t arguments on the MIPS N32 ABI.

[Mark H Weaver <mhw@netris.org>]

Hello all,

A failing glib test on MIPS N32 has alerted me to a bug in the handling
of unsigned 32-bit integers in libffi.  The MIPSpro N32 ABI Handbook [*]
states:

  "32-bit integer (int) parameters are always sign-extended when passed
   in registers, whether of signed or unsigned type.  [This issue does
   not arise in the o32-bit ABI.]"  (chapter 2, page 6)

[*] http://techpubs.sgi.com/library/manuals/2000/007-2816-005/pdf/007-2816-005.pdf

and indeed GCC generates code that assumes this.
For example, GCC 4.7.3 compiles:

--8<---------------cut here---------------start------------->8---
#include <stdint.h>
#include <stdlib.h>

void
do_test (uint32_t a)
{
  if (a != 4294967253U)
    exit (1);
}
--8<---------------cut here---------------end--------------->8---

as follows (with extraneous cruft stripped):

--8<---------------cut here---------------start------------->8---
do_test:
	li	$2,-43			# 0xffffffffffffffd5
	beq	$4,$2,.L5
	nop

	addiu	$sp,$sp,-16
	sd	$31,8($sp)
	jal	exit
	li	$4,1			# 0x1

.L5:
	j	$31
	nop
--8<---------------cut here---------------end--------------->8---

However, the current libffi code zero-extends 32-bit unsigned integers,
which violates this N32 FFI requirement.

See below for a patch to fix this problem.  I've tested this patch on
the preliminary port of GNU Guix to MIPS N32, which uses a minimally
patched GNU toolchain targetting mips64el-linux-gnu.

Without this patch, glib-2.38.0 fails its test suite, specifically the
gobject/test/signal.c test, which uses libffi to pass a large 32-bit
unsigned integer to a test function that checks the received value.
With this patch, glib-2.38.0 passes its test suite.

Comments and suggestions welcome.

     Regards,
       Mark


Signed-off-by: Mark H Weaver <mhw@netris.org>
---
 ChangeLog      |    5 +++++
 src/mips/ffi.c |    7 +++++++
 2 files changed, 12 insertions(+), 0 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index eceef84..e7e5d94 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2013-10-23  Mark H Weaver  <mhw@netris.org>
+
+	* src/mips/ffi.c: Fix handling of uint32_t arguments on the
+	MIPS N32 ABI.
+
 2013-10-13  Sandra Loosemore  <sandra@codesourcery.com>
 
 	* README: Add Nios II to table of supported platforms.
diff --git a/src/mips/ffi.c b/src/mips/ffi.c
index 03121e3..5d0dd70 100644
--- a/src/mips/ffi.c
+++ b/src/mips/ffi.c
@@ -170,7 +170,14 @@ static void ffi_prep_args(char *stack,
 		break;
 		  
 	      case FFI_TYPE_UINT32:
+#ifdef FFI_MIPS_N32
+		/* The N32 ABI requires that 32-bit integers
+		   be sign-extended to 64-bits, regardless of
+		   whether they are signed or unsigned. */
+		*(ffi_arg *)argp = *(SINT32 *)(* p_argv);
+#else
 		*(ffi_arg *)argp = *(UINT32 *)(* p_argv);
+#endif
 		break;
 
 	      /* This can only happen with 64bit slots.  */
-- 
1.7.5.4