Implement functions calls from within DDB on ia64. On ia64 a function

pointer doesn't point to the first instruction of that function, but
rather to a descriptor. The descriptor has the address of the first
instruction, as well as the value of the global pointer. The symbol
table doesn't know anything about descriptors, so if you lookup the
name of a function you get the address of the first instruction. The
cast from the address, which is the result of the symbol lookup, to a
function pointer as is done in db_fncall is therefore invalid.
Abstract this detail behind the DB_CALL macro. By default DB_CALL is
defined as db_fncall_generic, which yields the old behaviour. On ia64
the macro is defined as db_fncall_ia64, in which a descriptor is
constructed to yield a valid function pointer.

While here, introduce DB_MAXARGS. DB_MAXARGS replaces the existing
(local) MAXARGS. The DB_MAXARGS macro can be defined by platforms to
create a convenient maximum. By default this will be the legacy 10.
On ia64 we define this macro to be 8, for 8 is the maximum number of
arguments that can be passed in registers. This avoids having to
implement spilling of arguments on the memory stack.

Approved by: re (dwhite)

2 files changed, 24 insertions, 0 deletions

diff --git a/sys/ia64/ia64/db_interface.c b/sys/ia64/ia64/db_interface.c
index 53897b0644c2..6d8a188a33d4 100644
--- a/sys/ia64/ia64/db_interface.c
+++ b/sys/ia64/ia64/db_interface.c
@@ -46,6 +46,7 @@ __FBSDID("$FreeBSD$");
 
 #include <machine/db_machdep.h>
 #include <machine/frame.h>
+#include <machine/md_var.h>
 #include <machine/mutex.h>
 #include <machine/setjmp.h>
 
@@ -443,6 +444,25 @@ out:
 	return (loc + slot);
 }
 
+typedef db_expr_t __db_f(db_expr_t, db_expr_t, db_expr_t, db_expr_t, db_expr_t,
+    db_expr_t, db_expr_t, db_expr_t);
+
+register uint64_t __db_gp __asm__("gp");
+
+int
+db_fncall_ia64(db_expr_t addr, db_expr_t *rv, int nargs, db_expr_t args[])
+{
+	struct ia64_fdesc fdesc;
+	__db_f *f;
+
+	f = (__db_f *)&fdesc;
+	fdesc.func = addr;
+	fdesc.gp = __db_gp;	/* XXX doesn't work for modules. */
+	*rv = (*f)(args[0], args[1], args[2], args[3], args[4], args[5],
+	    args[6], args[7]);
+	return (1);
+}
+
 void
 db_show_mdpcpu(struct pcpu *pc)
 {
diff --git a/sys/ia64/include/db_machdep.h b/sys/ia64/include/db_machdep.h
index 5d5c7a5c0b81..cbf01a70e59f 100644
--- a/sys/ia64/include/db_machdep.h
+++ b/sys/ia64/include/db_machdep.h
@@ -73,4 +73,8 @@ void db_bkpt_skip(void);
 
 #define	branch_taken(ins, pc, regs) pc
 
+/* Function call support. */
+#define	DB_MAXARGS	8	/* Only support arguments in registers. */
+#define	DB_CALL		db_fncall_ia64
+
 #endif	/* _MACHINE_DB_MACHDEP_H_ */