[Dwarf-discuss] dwarf ver3.0: prologue_end and epilogue_begin bits

[Ramanaiah Nalamothu]

On 5/21/07, Ron Brender <ron.brender at charter.net> wrote:
>
> The prologue beginning and ending location are compiler code generation
> artifacts that do not correlate usefully with line number. For example,
> the same source might be input as
>
>      void foo (...) {...}
>
> or
>
>      void
>      foo (
>          ...)
>      {
>          ...
>      }
>
> The compiled code, hence the begin and end prologue addresses, will be
> identical,


how the both addresses will be same?? (see below assembly code)

but the line numbers will vary. The "normal" line-address
> correlation will naturally associate a line number with those same
> instructions--unrelated to the fact that they are begin or
> end prologue related; that is expected.


but with what line numbers i need to associate them with?? As i told you in
my first mail -1, -2 and 0 are the special line numbers that my compiler
will generate. I can't propagate them because they are not valid source line
numbers.

Here i am providing a sample source code and corresponding assembly code.
See my comments with # ......#.
.dbgline -1, .dbgline -2 and .dbgline 0 represents prologue_end,
epilogue_begin and end of function or epilogue.

test.c
---------------
int res;
extern void abort (void);
extern void exit (int);

struct baz
{
  int a, b, c, d, e;
};

void
bar (struct baz *x, int f, int g, int h, int i, int j)
{
  if (x->a != 1 || x->b != 2 || x->c != 3 || x->d != 4 || x->e != 5 ||
      f != 6 || g != 7 || h != 8 || i != 9 || j != 10)
    res = -1;
}

void
foo (char *z, struct baz x, char *y)
{
  bar (&x, 6, 7, 8, 9, 10);



}
int main (){
  struct baz x;

  x.a = 1;
  x.b = 2;
  x.c = 3;
  x.d = 4;
  x.e = 5;
  foo ((char *) 0, x, (char *) 0);

  if (res == -1)
    return 0;
  else
    return 1;

}
------------------------------------------

test.s
-------------------
    .dbfile C:\cygwin\home\Administrator\Arm\test.c
    AREA    "C$$code", CODE, READONLY
    CODE32
    ALIGN 4
    .dbfile C:\cygwin\home\Administrator\Arm\test.c
    EXPORT _main
;    .dbfunc e main _main fI
    AREA    "C$$code", CODE, READONLY
    CODE32
    ALIGN 4
_main:
    stmfd R13!,{R14}
    .dbline -1                        # indicates prologue_end #
    .dbline 3
; #include <stdio.h>
; int main()
; {
    .dbline 4
;  if( 1 )
    .dbline 5
;       goto label;
    b L4
L5:
    .dbline 9
;     else
;          goto lab;
; lab:
;  foo(10);
    mov R0,#10
    bl _foo
L4:
    .dbline 11
; label:
;  return 0;
    mov R0,#0
    .dbline -2                                 # indicates epilogue_begin #
L1:
    ldmfd R13!,{R15}
    .dbline 0 ; func end                    # indicates end of epilogue.
Here begin and end addresses or not same as you suggested #
    .dbfile C:\cygwin\home\Administrator\Arm\test.c
;    .dbend
;    .dbfunc s foo _foo fI
    AREA    "C$$code", CODE, READONLY
    CODE32
    ALIGN 4
;          value -> R4
_foo:
    mov R12,R13
    stmfd R13!,{R4,R12,R14}
    mov R4,R0
    .dbline -1
    .dbline 15
; }
;
; static int foo(int value)
; {
    .dbline 16
;  return 0;
    mov R0,#0
    .dbline -2
L6:
    ldmfd R13!,{R4,SP,R15}
    .dbline 0 ; func end
    .dbfile C:\cygwin\home\Administrator\Arm\test.c
;    .dbsym r value 4 I
;    .dbend
    END
------------------------------------------------------------------

So if the debugger needs line numbers info what should be the line numbers
for these prologue and epilogue cases?

Thanks for your replies.

Regards,
Ramana


Ron
>
> --------------------------
> Ramanaiah Nalamothu wrote:
> > Hi,
> >
> >  I am working at assembler context to emit the ELF-DWARF(dwarf ver3.0).
> > I need to set the bits prologue_end and epilogue_begin. My compiler
> > emits debug directive with specific -ve line numbers to indicate
> > prologue_end and epilogue_begin. But they are not acceptable line
> > numbers in source file.
> > My doubt is, do I need to associate the their occurance with the source
> > line numbers or is it sufficient just to tell at what 'address' the
> > prologue_end or epilogue_begin occur? If debugger needs line number,
> > what line numbers should be emitted in my case?
> >
> > Thanks in advance for your replies.
> >
> > Regards,
> > Ramana
>
>
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