[RFC/RFA] PING: skip __main

["Pierre Muller" <muller at ics dot u-strasbg dot fr>]

  Pedro submitted this patch end of January,
but the 6.8 release pushed it to a later date.
http://sourceware.org/ml/gdb-patches/2008-01/msg00665.html
  
Now that GDB 6.8 is out, 
I would really like to get this patch in.
Pedro, this is your work, but you seem to be
much more involved in other things lately,
thus, if you don't mind, I can try to push this through. 

  I updated the patch from the first message
referenced and just followed Daniel's advice in
http://sourceware.org/ml/gdb-patches/2008-01/msg00883.html
to change skip___main into skip_main_constructor.

  This __main call seems to be
a common feature for coff format, thus 
I suppose that it applies to other targets,
go32v2 djgpp is probably one of them.

For cygwin target, I get this:

                === gdb Summary ===
	
-# of expected passes           10733
-# of unexpected failures       560
+# of expected passes           10928
+# of unexpected failures       363
 # of expected failures         59
 # of unknown successes         2
-# of known failures            21
+# of known failures            23
 # of unresolved testcases      40
 # of untested testcases                14
 # of unsupported tests         23

  Almost 200 failures less...

  Daniel wanted to get a comment from Mark
in his last email in that thread, that is the reason
why I added Mark Kettenis to the list of recipients.

Does this patch look OK now?

  One point that should still be discussed is
if we should call main_name function
rather than hardcoded "main" in find_function_start_sal in symtab.c.

Pierre Muller
Pascal language support maintainer for GDB


2008-05-02  Pedro Alves  <pedro_alves@portugalmail.pt>
	Pierre Muller  <muller@ics.u-strasbg.fr>

	* gdbarch.sh (gdbarch_skip_main_constructor_call): New.
	* gdbarch.h, gdbarch.c: Regenerate.

	* i386-tdep.h (i386_skip_main_constructor_call): Declare.
	* i386-tdep.c (i386_skip_main_constructor_call): New.
	* i386-cygwin-tdep.c (i386_cygwin_init_abi): Register
	i386_skip_main_constructor_call as
gdbarch_skip_main_constructor_call 
	gdbarch callback.
	* symtab.c (find_function_start_sal): When pc points at the "main"
	function, call gdbarch_skip_main_constructor_call.

Index: gdb/gdbarch.c
===================================================================
RCS file: /cvs/src/src/gdb/gdbarch.c,v
retrieving revision 1.422
diff -u -p -r1.422 gdbarch.c
--- gdb/gdbarch.c	22 Apr 2008 11:03:41 -0000	1.422
+++ gdb/gdbarch.c	30 Apr 2008 13:01:33 -0000
@@ -184,6 +184,7 @@ struct gdbarch
   gdbarch_integer_to_address_ftype *integer_to_address;
   gdbarch_return_value_ftype *return_value;
   gdbarch_skip_prologue_ftype *skip_prologue;
+  gdbarch_skip_main_constructor_call_ftype *skip_main_constructor_call;
   gdbarch_inner_than_ftype *inner_than;
   gdbarch_breakpoint_from_pc_ftype *breakpoint_from_pc;
   gdbarch_adjust_breakpoint_address_ftype *adjust_breakpoint_address;
@@ -306,6 +307,7 @@ struct gdbarch startup_gdbarch =
   0,  /* integer_to_address */
   0,  /* return_value */
   0,  /* skip_prologue */
+  0,  /* skip_main_constructor_call */
   0,  /* inner_than */
   0,  /* breakpoint_from_pc */
   0,  /* adjust_breakpoint_address */
@@ -542,6 +544,7 @@ verify_gdbarch (struct gdbarch *gdbarch)
   /* Skip verify of return_value, has predicate */
   if (gdbarch->skip_prologue == 0)
     fprintf_unfiltered (log, "\n\tskip_prologue");
+  /* Skip verify of skip_main_constructor_call, has predicate */
   if (gdbarch->inner_than == 0)
     fprintf_unfiltered (log, "\n\tinner_than");
   if (gdbarch->breakpoint_from_pc == 0)
@@ -934,6 +937,12 @@ gdbarch_dump (struct gdbarch *gdbarch, s
                       "gdbarch_dump: single_step_through_delay =
<0x%lx>\n",
                       (long) gdbarch->single_step_through_delay);
   fprintf_unfiltered (file,
+                      "gdbarch_dump: gdbarch_skip_main_constructor_call_p()
= %d\n",
+                      gdbarch_skip_main_constructor_call_p (gdbarch));
+  fprintf_unfiltered (file,
+                      "gdbarch_dump: skip_main_constructor_call =
<0x%lx>\n",
+                      (long) gdbarch->skip_main_constructor_call);
+  fprintf_unfiltered (file,
                       "gdbarch_dump: gdbarch_skip_permanent_breakpoint_p()
= %d\n",
                       gdbarch_skip_permanent_breakpoint_p (gdbarch));
   fprintf_unfiltered (file,
@@ -2075,6 +2084,30 @@ set_gdbarch_skip_prologue (struct gdbarc
 }
 
 int
+gdbarch_skip_main_constructor_call_p (struct gdbarch *gdbarch)
+{
+  gdb_assert (gdbarch != NULL);
+  return gdbarch->skip_main_constructor_call != NULL;
+}
+
+CORE_ADDR
+gdbarch_skip_main_constructor_call (struct gdbarch *gdbarch, CORE_ADDR ip)
+{
+  gdb_assert (gdbarch != NULL);
+  gdb_assert (gdbarch->skip_main_constructor_call != NULL);
+  if (gdbarch_debug >= 2)
+    fprintf_unfiltered (gdb_stdlog, "gdbarch_skip_main_constructor_call
called\n");
+  return gdbarch->skip_main_constructor_call (gdbarch, ip);
+}
+
+void
+set_gdbarch_skip_main_constructor_call (struct gdbarch *gdbarch,
+                              gdbarch_skip_main_constructor_call_ftype
skip_main_constructor_call)
+{
+  gdbarch->skip_main_constructor_call = skip_main_constructor_call;
+}
+
+int
 gdbarch_inner_than (struct gdbarch *gdbarch, CORE_ADDR lhs, CORE_ADDR rhs)
 {
   gdb_assert (gdbarch != NULL);
Index: gdb/gdbarch.h
===================================================================
RCS file: /cvs/src/src/gdb/gdbarch.h,v
retrieving revision 1.377
diff -u -p -r1.377 gdbarch.h
--- gdb/gdbarch.h	29 Apr 2008 16:06:07 -0000	1.377
+++ gdb/gdbarch.h	30 Apr 2008 13:01:33 -0000
@@ -381,6 +381,12 @@ typedef CORE_ADDR (gdbarch_skip_prologue
 extern CORE_ADDR gdbarch_skip_prologue (struct gdbarch *gdbarch, CORE_ADDR
ip);
 extern void set_gdbarch_skip_prologue (struct gdbarch *gdbarch,
gdbarch_skip_prologue_ftype *skip_prologue);
 
+extern int gdbarch_skip_main_constructor_call_p (struct gdbarch *gdbarch);
+
+typedef CORE_ADDR (gdbarch_skip_main_constructor_call_ftype) (struct
gdbarch *gdbarch, CORE_ADDR ip);
+extern CORE_ADDR gdbarch_skip_main_constructor_call (struct gdbarch
*gdbarch, CORE_ADDR ip);
+extern void set_gdbarch_skip_main_constructor_call (struct gdbarch
*gdbarch, gdbarch_skip_main_constructor_call_ftype
*skip_main_constructor_call);
+
 typedef int (gdbarch_inner_than_ftype) (CORE_ADDR lhs, CORE_ADDR rhs);
 extern int gdbarch_inner_than (struct gdbarch *gdbarch, CORE_ADDR lhs,
CORE_ADDR rhs);
 extern void set_gdbarch_inner_than (struct gdbarch *gdbarch,
gdbarch_inner_than_ftype *inner_than);
Index: gdb/gdbarch.sh
===================================================================
RCS file: /cvs/src/src/gdb/gdbarch.sh,v
retrieving revision 1.463
diff -u -p -r1.463 gdbarch.sh
--- gdb/gdbarch.sh	29 Apr 2008 16:06:06 -0000	1.463
+++ gdb/gdbarch.sh	30 Apr 2008 13:01:34 -0000
@@ -483,6 +483,7 @@ M:CORE_ADDR:integer_to_address:struct ty
 M:enum return_value_convention:return_value:struct type *functype, struct
type *valtype, struct regcache *regcache, gdb_byte *readbuf, const gdb_byte
*writebuf:functype, valtype, regcache, readbuf, writebuf
 
 m:CORE_ADDR:skip_prologue:CORE_ADDR ip:ip:0:0
+M:CORE_ADDR:skip_main_constructor_call:CORE_ADDR ip:ip
 f:int:inner_than:CORE_ADDR lhs, CORE_ADDR rhs:lhs, rhs:0:0
 m:const gdb_byte *:breakpoint_from_pc:CORE_ADDR *pcptr, int *lenptr:pcptr,
lenptr::0:
 M:CORE_ADDR:adjust_breakpoint_address:CORE_ADDR bpaddr:bpaddr
Index: gdb/i386-cygwin-tdep.c
===================================================================
RCS file: /cvs/src/src/gdb/i386-cygwin-tdep.c,v
retrieving revision 1.16
diff -u -p -r1.16 i386-cygwin-tdep.c
--- gdb/i386-cygwin-tdep.c	1 Jan 2008 22:53:10 -0000	1.16
+++ gdb/i386-cygwin-tdep.c	30 Apr 2008 13:01:34 -0000
@@ -227,6 +227,8 @@ i386_cygwin_init_abi (struct gdbarch_inf
 
   set_gdbarch_skip_trampoline_code (gdbarch,
i386_cygwin_skip_trampoline_code);
 
+  set_gdbarch_skip_main_constructor_call (gdbarch,
i386_skip_main_constructor_call);
+
   tdep->struct_return = reg_struct_return;
 
   tdep->gregset_reg_offset = i386_win32_gregset_reg_offset;
Index: gdb/i386-tdep.c
===================================================================
RCS file: /cvs/src/src/gdb/i386-tdep.c,v
retrieving revision 1.255
diff -u -p -r1.255 i386-tdep.c
--- gdb/i386-tdep.c	25 Apr 2008 14:57:30 -0000	1.255
+++ gdb/i386-tdep.c	30 Apr 2008 13:01:35 -0000
@@ -941,6 +941,33 @@ i386_skip_prologue (struct gdbarch *gdba
   return pc;
 }
 
+/* Check that the code pointed to by PC corresponds to a call to
+   __main, skip it if so.  Return PC otherwise.  */
+
+CORE_ADDR
+i386_skip_main_constructor_call (struct gdbarch *gdbarch, CORE_ADDR pc)
+{
+  gdb_byte op;
+
+  target_read_memory (pc, &op, 1);
+  if (op == 0xe8)
+    {
+      gdb_byte buf[4];
+      if (target_read_memory (pc + 1, buf, sizeof buf) == 0)
+ 	{
+ 	  CORE_ADDR call_dest = pc + 5 + extract_unsigned_integer (buf, 4);
+
+ 	  struct minimal_symbol *s = lookup_minimal_symbol_by_pc
(call_dest);
+ 	  if (s != NULL
+ 	      && SYMBOL_LINKAGE_NAME (s) != NULL
+ 	      && strcmp (SYMBOL_LINKAGE_NAME (s), "__main") == 0)
+ 	    pc += 5;
+ 	}
+    }
+
+  return pc;
+}
+
 /* This function is 64-bit safe.  */
 
 static CORE_ADDR
Index: gdb/i386-tdep.h
===================================================================
RCS file: /cvs/src/src/gdb/i386-tdep.h,v
retrieving revision 1.53
diff -u -p -r1.53 i386-tdep.h
--- gdb/i386-tdep.h	11 Mar 2008 05:21:38 -0000	1.53
+++ gdb/i386-tdep.h	30 Apr 2008 13:01:35 -0000
@@ -166,6 +166,7 @@ extern struct type *i386_sse_type (struc
 
 /* Functions exported from i386-tdep.c.  */
 extern CORE_ADDR i386_pe_skip_trampoline_code (CORE_ADDR pc, char *name);
+extern CORE_ADDR i386_skip_main_constructor_call (struct gdbarch *gdbarch,
CORE_ADDR pc);
 
 /* Return the name of register REGNUM.  */
 extern char const *i386_register_name (struct gdbarch * gdbarch, int
regnum);
Index: gdb/symtab.c
===================================================================
RCS file: /cvs/src/src/gdb/symtab.c,v
retrieving revision 1.177
diff -u -p -r1.177 symtab.c
--- gdb/symtab.c	19 Apr 2008 11:39:50 -0000	1.177
+++ gdb/symtab.c	30 Apr 2008 13:01:36 -0000
@@ -2572,6 +2572,21 @@ find_function_start_sal (struct symbol *
       /* Recalculate the line number (might not be N+1).  */
       sal = find_pc_sect_line (pc, SYMBOL_BFD_SECTION (sym), 0);
     }
+
+  /* On targets with executable formats that don't have a concept of
+     constructors (ELF with .init has, PE doesn't), gcc emits a call
+     to `__main' in `main' between the prologue and before user
+     code.  */
+  if (funfirstline
+      && gdbarch_skip_main_constructor_call_p (current_gdbarch)
+      && SYMBOL_LINKAGE_NAME (sym)
+      && strcmp (SYMBOL_LINKAGE_NAME (sym), "main") == 0)
+    {
+      pc = gdbarch_skip_main_constructor_call (current_gdbarch, pc);
+      /* Recalculate the line number (might not be N+1).  */
+      sal = find_pc_sect_line (pc, SYMBOL_BFD_SECTION (sym), 0);
+    }
+
   sal.pc = pc;
 
   return sal;