Import various libgcc functions from syslinux.

Experimentation reveals that gcc ignores -mrtd for the implicit
arithmetic functions (e.g. __udivdi3), but not for the implicit
memcpy() and memset() functions.  Mark the implicit arithmetic
functions with __attribute__((cdecl)) to compensate for this.

(Note: we cannot mark with with __cdecl, because we define __cdecl to
incorporate regparm(0) as well.)

src/libgcc/__divdi3.c

@@ -0,0 +1,26 @@
+/*
+ * arch/i386/libgcc/__divdi3.c
+ */
+
+#include "libgcc.h"
+
+LIBGCC int64_t __divdi3(int64_t num, int64_t den)
+{
+  int minus = 0;
+  int64_t v;
+
+  if ( num < 0 ) {
+    num = -num;
+    minus = 1;
+  }
+  if ( den < 0 ) {
+    den = -den;
+    minus ^= 1;
+  }
+
+  v = __udivmoddi4(num, den, NULL);
+  if ( minus )
+    v = -v;
+
+  return v;
+}

src/libgcc/__moddi3.c

@@ -0,0 +1,26 @@
+/*
+ * arch/i386/libgcc/__moddi3.c
+ */
+
+#include "libgcc.h"
+
+LIBGCC int64_t __moddi3(int64_t num, int64_t den)
+{
+  int minus = 0;
+  int64_t v;
+
+  if ( num < 0 ) {
+    num = -num;
+    minus = 1;
+  }
+  if ( den < 0 ) {
+    den = -den;
+    minus ^= 1;
+  }
+
+  (void) __udivmoddi4(num, den, (uint64_t *)&v);
+  if ( minus )
+    v = -v;
+
+  return v;
+}

src/libgcc/__udivdi3.c

@@ -0,0 +1,10 @@
+/*
+ * arch/i386/libgcc/__divdi3.c
+ */
+
+#include "libgcc.h"
+
+LIBGCC uint64_t __udivdi3(uint64_t num, uint64_t den)
+{
+  return __udivmoddi4(num, den, NULL);
+}

src/libgcc/__udivmoddi4.c

@@ -0,0 +1,32 @@
+#include "libgcc.h"
+
+LIBGCC uint64_t __udivmoddi4(uint64_t num, uint64_t den, uint64_t *rem_p)
+{
+  uint64_t quot = 0, qbit = 1;
+
+  if ( den == 0 ) {
+    return 1/((unsigned)den); /* Intentional divide by zero, without
+				 triggering a compiler warning which
+				 would abort the build */
+  }
+
+  /* Left-justify denominator and count shift */
+  while ( (int64_t)den >= 0 ) {
+    den <<= 1;
+    qbit <<= 1;
+  }
+
+  while ( qbit ) {
+    if ( den <= num ) {
+      num -= den;
+      quot += qbit;
+    }
+    den >>= 1;
+    qbit >>= 1;
+  }
+
+  if ( rem_p )
+    *rem_p = num;
+
+  return quot;
+}

src/libgcc/__umoddi3.c

@@ -0,0 +1,13 @@
+/*
+ * arch/i386/libgcc/__umoddi3.c
+ */
+
+#include "libgcc.h"
+
+LIBGCC uint64_t __umoddi3(uint64_t num, uint64_t den)
+{
+  uint64_t v;
+
+  (void) __udivmoddi4(num, den, &v);
+  return v;
+}

src/libgcc/libgcc.h

@@ -0,0 +1,26 @@
+#ifndef _LIBGCC_H
+#define _LIBGCC_H
+
+#include <stdint.h>
+#include <stddef.h>
+
+/*
+ * It seems as though gcc expects its implicit arithmetic functions to
+ * be cdecl, even if -mrtd is specified.  This is somewhat
+ * inconsistent; for example, if -mregparm=3 is used then the implicit
+ * functions do become regparm(3).
+ *
+ * The implicit calls to memcpy() and memset() which gcc can generate
+ * do not seem to have this inconsistency; -mregparm and -mrtd affect
+ * them in the same way as any other function.
+ *
+ */
+#define LIBGCC __attribute__ (( cdecl ))
+
+extern LIBGCC uint64_t __udivmoddi4(uint64_t num, uint64_t den, uint64_t *rem);
+extern LIBGCC uint64_t __udivdi3(uint64_t num, uint64_t den);
+extern LIBGCC uint64_t __umoddi3(uint64_t num, uint64_t den);
+extern LIBGCC int64_t __divdi3(int64_t num, int64_t den);
+extern LIBGCC int64_t __moddi3(int64_t num, int64_t den);
+
+#endif /* _LIBGCC_H */

src/libgcc/memcpy.c

@@ -0,0 +1,18 @@
+/** @file
+ *
+ * gcc sometimes likes to insert implicit calls to memcpy().
+ * Unfortunately, there doesn't seem to be any way to prevent it from
+ * doing this, or to force it to use the optimised memcpy() as seen by
+ * C code; it insists on inserting a symbol reference to "memcpy".  We
+ * therefore include wrapper functions just to keep gcc happy.
+ *
+ */
+
+#include <string.h>
+
+void * gcc_implicit_memcpy ( void *dest, const void *src,
+			     size_t len ) asm ( "memcpy" );
+
+void * gcc_implicit_memcpy ( void *dest, const void *src, size_t len ) {
+	return memcpy ( dest, src, len );
+}