* sparc-tdep.c (sparc_gdbarch_init): Add comment explaining why

ON_STACK is needed.

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 16bf4f7..99733a9 100644 (file)
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,8 @@
+2002-04-26  Andrew Cagney  <ac131313@redhat.com>
+
+       * sparc-tdep.c (sparc_gdbarch_init): Add comment explaining why
+       ON_STACK is needed.
+
 2002-04-26  Ben Elliston  <bje@redhat.com>
 
        * target.c (do_xfer_memory): Correct reference to the new option

diff --git a/gdb/sparc-tdep.c b/gdb/sparc-tdep.c
index 4f7f57b..28c51dc 100644 (file)
--- a/gdb/sparc-tdep.c
+++ b/gdb/sparc-tdep.c
@@ -3026,6 +3026,50 @@ sparc_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)
       set_gdbarch_call_dummy_address (gdbarch, sparc_call_dummy_address);
       set_gdbarch_call_dummy_breakpoint_offset (gdbarch, 0x30);
       set_gdbarch_call_dummy_length (gdbarch, 0x38);
+
+      /* NOTE: cagney/2002-04-26: Based from info posted by Peter
+        Schauer around Oct '99.  Briefly, due to aspects of the SPARC
+        ABI, it isn't possible to use ON_STACK with a strictly
+        compliant compiler.
+
+        Peter Schauer writes ...
+
+        No, any call from GDB to a user function returning a
+        struct/union will fail miserably. Try this:
+
+        *NOINDENT*
+        struct x
+        {
+           int a[4];
+         };
+
+        struct x gx;
+
+        struct x
+        sret ()
+        {
+          return gx;
+        }
+
+        main ()
+        {
+          int i;
+          for (i = 0; i < 4; i++)
+            gx.a[i] = i + 1;
+          gx = sret ();
+        }
+        *INDENT*
+
+        Set a breakpoint at the gx = sret () statement, run to it and
+        issue a `print sret()'. It will not succed with your
+        approach, and I doubt that continuing the program will work
+        as well.
+
+        For details of the ABI see the Sparc Architecture Manual.  I
+        have Version 8 (Prentice Hall ISBN 0-13-825001-4) and the
+        calling conventions for functions returning aggregate values
+        are explained in Appendix D.3.  */
+
       set_gdbarch_call_dummy_location (gdbarch, ON_STACK);
       set_gdbarch_call_dummy_words (gdbarch, call_dummy_32);
 #else