How to debug ruby source code using gdb?, can't print array content

7stud2 · 22 June 2012 04:55

I tried something like this in array.c

rb_ary_initialize(int argc, VALUE *argv, VALUE ary)
{
  long len;
  int ln;
  int *ar;
  VALUE size, val;
  switch (TYPE(ary)) {
    case T_FIXNUM:
      break;
    case T_STRING:
      break;
    case T_ARRAY:
      ar=RARRAY(ary);
      ln=RARRAY_LEN(ary);
      printf("ln: %d\n",ln);
      ar=RARRAY_PTR(ary);
      break;
    default:
      rb_raise(rb_eTypeError, "not valid value");
      break;
  }

gdb ./ruby
(gdb)run
ctrl+c
(gdb)break array.c:rb_ary_initialize
(gdb)continue
arr=Array.new(3)
arr[0]=5
arr[1]=7
ctrl+d
(gdb)next

But i can't understand how to print the value using printf(); in
array.c:rb_ary_initialize function doing some casting.

Can anyone post reply with example to do it?

github.com

ruby/ruby/blob/0b0dea752c0ef35d1a964b812a1a7fd033ab9e2e/README.EXT#L125


is a String.  Notice that the macros take only the lvalue as their
argument, to change the value of var in place.


You can also use the macro named StringValueCStr(). This is just
like StringValuePtr(), but always add nul character at the end of
the result. If the result contains nul character, this macro causes
the ArgumentError exception.
StringValuePtr() doesn't guarantee the existence of a nul at the end
of the result, and the result may contain nul.


Other data types have corresponding C structures, e.g. struct RArray
for T_ARRAY etc. The VALUE of the type which has the corresponding
structure can be cast to retrieve the pointer to the struct.  The
casting macro will be of the form RXXXX for each data type; for
instance, RARRAY(obj).  See "ruby.h".


There are some accessing macros for structure members, for example
`RSTRING_LEN(str)' to get the size of the Ruby String object.  The
allocated region can be accessed by `RSTRING_PTR(str)'.  For arrays,
use `RARRAY_LEN(ary)' and `RARRAY_PTR(ary)' respectively.

github.com

ruby/ruby/blob/0b0dea752c0ef35d1a964b812a1a7fd033ab9e2e/array.c#L569


*  version which uses the result of that block each time an element
*  of the array needs to be initialized:
*
*     a = Array.new(2) { Hash.new }
*     a[0]['cat'] = 'feline'
*     a # => [{"cat"=>"feline"}, {}]
*
*/


static VALUE
rb_ary_initialize(int argc, VALUE *argv, VALUE ary)
{
   long len;
   VALUE size, val;


   rb_ary_modify(ary);
   if (argc == 0) {
	if (ARY_OWNS_HEAP_P(ary) && RARRAY_PTR(ary)) {
	    xfree(RARRAY_PTR(ary));
	}
       rb_ary_unshare_safe(ary);

Thanks.

···

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Alex_Newone · 22 June 2012 07:35

Ruby has GDB helpers. Take a look at https://github.com/ruby/ruby/blob/trunk/.gdbinit
Fo instance rp prints any ruby value. There are other handy helpers as well.

···

On Jun 22, 2012, at 7:55 AM, gmspro gmspro wrote:

I tried something like this in array.c

rb_ary_initialize(int argc, VALUE *argv, VALUE ary)
{
long len;
int ln;
int *ar;
VALUE size, val;
switch (TYPE(ary)) {
   case T_FIXNUM:
     break;
   case T_STRING:
     break;
   case T_ARRAY:
     ar=RARRAY(ary);
     ln=RARRAY_LEN(ary);
     printf("ln: %d\n",ln);
     ar=RARRAY_PTR(ary);
     break;
   default:
     rb_raise(rb_eTypeError, "not valid value");
     break;
}

gdb ./ruby
(gdb)run
ctrl+c
(gdb)break array.c:rb_ary_initialize
(gdb)continue
arr=Array.new(3)
arr[0]=5
arr[1]=7
ctrl+d
(gdb)next

But i can't understand how to print the value using printf(); in
array.c:rb_ary_initialize function doing some casting.

Can anyone post reply with example to do it?

ruby/README.EXT at 0b0dea752c0ef35d1a964b812a1a7fd033ab9e2e · ruby/ruby · GitHub

ruby/array.c at 0b0dea752c0ef35d1a964b812a1a7fd033ab9e2e · ruby/ruby · GitHub

Thanks.

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7stud2 · 22 June 2012 08:49

Alex Newone wrote in post #1065644:

Ruby has GDB helpers. Take a look at
https://github.com/ruby/ruby/blob/trunk/.gdbinit
Fo instance rp prints any ruby value. There are other handy helpers as
well.

How to use that .gdbinit?
https://github.com/ruby/ruby/blob/trunk/.gdbinit

···

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Ryan_Davis1 · 22 June 2012 22:34

FYI, this is a help vampire that we recently banned on IRC. He has a long history of this.

···

On Jun 22, 2012, at 00:35 , Sigurd wrote:

Ruby has GDB helpers. Take a look at https://github.com/ruby/ruby/blob/trunk/.gdbinit
Fo instance rp prints any ruby value. There are other handy helpers as well.

Alex_Newone · 22 June 2012 09:22

Copy it to the home folder and it'll be automatically loaded by gdb.

···

On Jun 22, 2012, at 11:49 AM, gmspro gmspro wrote:

Alex Newone wrote in post #1065644:

Ruby has GDB helpers. Take a look at
https://github.com/ruby/ruby/blob/trunk/.gdbinit
Fo instance rp prints any ruby value. There are other handy helpers as
well.

How to use that .gdbinit?
https://github.com/ruby/ruby/blob/trunk/.gdbinit

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7stud2 · 23 June 2012 01:34

Ryan Davis wrote in post #1065745:

Ruby has GDB helpers. Take a look at

https://github.com/ruby/ruby/blob/trunk/.gdbinit

Fo instance rp prints any ruby value. There are other handy helpers as well.

FYI, this is a help vampire that we recently banned on IRC. He has a
long history of this.

No, i have tried this,

arr=Array.new(3)
arr[0]=5
arr[1]=3
arr[2]=2

These lines should call this function,
https://github.com/ruby/ruby/blob/trunk/array.c#L568 according to this,
http://www.ruby-doc.org/core-1.9.3/Array.html

So I have added couple of lines there to display the values of array.
But i didn't get the expected result.

else {
    memfill(RARRAY_PTR(ary), len, val);
    ARY_SET_LEN(ary, len);
    int i;
    int result;
    result = 0;
    VALUE *s_arr = RARRAY_PTR(ary);
    for(i = 0; i < len; i++) {
        result = LONG2NUM(s_arr[i]);
        printf("r: %d\n",result);
    }
}

I got the result like this:

arr=Array.new(3)
arr[0]=5
arr[1]=3
arr[2]=2
r: 9
r: 9
r: 9

Why is this result? Why 9?

I have followed these to solve it:

How to convert ruby array to C array with RubyInline?

https://github.com/ruby/ruby/blob/trunk/README.EXT#L131

https://github.com/ruby/ruby/blob/trunk/include/ruby/ruby.h#L708

https://github.com/ruby/ruby/blob/trunk/include/ruby/ruby.h#L731

Also tried this, result = NUM2LONG(s_arr[i]); result =
FIX2NUM(s_arr[i]); result = rb_long2int(s_arr[i]); nothing gets the
expected result.

Can anyone please help to display/printf the value of ruby array in C?

Any reply/answer will be highly appreciated.

Thanks in advanced.

···

On Jun 22, 2012, at 00:35 , Sigurd wrote:

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7stud2 · 22 June 2012 15:20

Alex Newone wrote in post #1065660:

Copy it to the home folder and it'll be automatically loaded by gdb.

I did this. But it looks, it doesn't help or do anything from (gdb).

···

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How to debug ruby source code using gdb?, can't print array content

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