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Re: [RFC/RFA] PING: skip __main


A Friday 02 May 2008 14:25:44, Pierre Muller wrote:
>   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 don't mind at all.  I even thank you.  :-)

>   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.
>

I believe "__main" is only emitted by gcc in the "main"
entry point.  I'd expect other gcc languages' runtimes
to have something like this somewhere in the startup routines:

 int
 main ()
 {
        initialize_my_lang_runtime ();
	mylang_entry_point ();
 }

In gcc the call is emitted in:

void
expand_main_function (void)
{
#if (defined(INVOKE__main)                              \
     || (!defined(HAS_INIT_SECTION)                     \
         && !defined(INIT_SECTION_ASM_OP)               \
         && !defined(INIT_ARRAY_SECTION_ASM_OP)))
  emit_library_call (init_one_libfunc (NAME__MAIN), LCT_NORMAL, VOIDmode, 0);
#endif
}

And that is called like so:

  /* If this function is `main', emit a call to `__main'
     to run global initializers, etc.  */
  if (DECL_NAME (current_function_decl)
      && MAIN_NAME_P (DECL_NAME (current_function_decl))
      && DECL_FILE_SCOPE_P (current_function_decl))
    expand_main_function ();

#define MAIN_NAME_P(NODE) \
    (IDENTIFIER_NODE_CHECK (NODE) == main_identifier_node)

#define main_identifier_node             global_trees[TI_MAIN_IDENTIFIER]

I can only find C variants and ADA setting main_identifier_node,
and it's always on "main".  So, the ADA case alone invalidates usage
of main_name in this case.

ada/utils.c:763:  main_identifier_node = get_identifier ("main");
c-common.c:3912:  main_identifier_node = get_identifier ("main");

gdb/ada-lang.c:
/* The name of the symbol to use to get the name of the main subprogram.  */
static const char ADA_MAIN_PROGRAM_SYMBOL_NAME[]
  = "__gnat_ada_main_program_name";

> 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;


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