[PATCH] i386_skip_prologue.

[Pedro Alves <pedro_alves at portugalmail dot pt>]

Hi all,

(moving this from gdb@, also at http://sources.redhat.com/ml/gdb/2006-11/msg00140.html)

Daniel Jacobowitz escreveu:
> On Sat, Nov 18, 2006 at 03:31:32PM +0000, Pedro Alves wrote:
> >     .loc 1 15 0
> >     pushl     %ebp
> > LCFI0:
> >     movl $16, %eax
> >     movl %esp, %ebp
> > LCFI1:
> >     subl $8, %esp
> > LCFI2:
> >     .loc 1 15 0
> >     andl $-16, %esp
> >     call __alloca
> >     call ___main
> >     .loc 1 17 0
>
> > What do you think could be done to fix this?
> > Is it the .loc directives that are being output wrong? Or is it gdb's 
> > prologue reader
> > (if there is such a thing) that is missing the fact that __main is not 
> > user code?
>
> Probably both.  The second line number marker normally marks the end of
> the prologue, so GCC is wrong, and GDB might have to be taught about
> _alloca and __main.

The i386 targets currently don't look at line number markers
or the symbol table at all in i386_skip_prologue.

I used the attached patch to test the gcc side of the fix,
(http://gcc.gnu.org/ml/gcc-patches/2006-12/msg00633.html)

With the gcc patch above applied, this patch fixes all the runto_main issues
on Cygwin. There are a few other FAILs related to breakpoints and main,
but those are testsuite bugs, unrelated to this. I will send patches for those shortly.

This are my current Cygwin/i386 results:

		=== gdb Summary ===

# of expected passes		9897
# of unexpected failures	423
# of unexpected successes	1
# of expected failures		45
# of unknown successes		3
# of known failures		60
# of unresolved testcases	1
# of untested testcases		12
# of unsupported tests		26

(A lot of those seem to be signals related. I guess there are only a
couple of bugs producing all of those failures.)

Cheers,
Pedro Alves

---

2006-12-09  Pedro Alves  <pedro_alves@portugalmail.pt>

        * i386-tdep.c (i386_skip_prologue): Try to find the end of the
        prologue using the symbol table.

Index: i386-tdep.c
===================================================================
RCS file: /cvs/src/src/gdb/i386-tdep.c,v
retrieving revision 1.225
diff -u -p -r1.225 i386-tdep.c
--- i386-tdep.c	8 Aug 2006 21:36:46 -0000	1.225
+++ i386-tdep.c	9 Dec 2006 19:30:25 -0000
@@ -825,6 +825,29 @@ i386_skip_prologue (CORE_ADDR start_pc)
   CORE_ADDR pc;
   gdb_byte op;
   int i;
+  char *func_name;
+  CORE_ADDR func_addr, func_end = 0;
+
+  /* See what the symbol table says.  */
+
+  if (find_pc_partial_function (start_pc, &func_name, &func_addr, &func_end))
+    {
+      struct symbol *sym;
+      struct symtab_and_line sal;
+
+      /* Found a function.  */
+      sym = lookup_symbol (func_name, NULL, VAR_DOMAIN, NULL, NULL);
+      if (sym && SYMBOL_LANGUAGE (sym) != language_asm)
+        {
+          /* Don't use this trick for assembly source files.  */
+          sal = find_pc_line (func_addr, 0);
+          if ((sal.line != 0) && (sal.end < func_end))
+            return sal.end;
+        }
+    }
+
+  /* Can't find the prologue end in the symbol table, try it the hard way
+     by disassembling the instructions.  */
 
   cache.locals = -1;
   pc = i386_analyze_prologue (start_pc, 0xffffffff, &cache);