[PATCH 05/15] dwarf_getsrclines.c: Add locking

[Mark Wielaard]

On Sun, Jan 19, 2025 at 10:20:31PM -0500, Aaron Merey wrote:
> 	* libdw/dwarf_getsrclines.c (dwarf_getsrclines): Use dwarf_lock.

So same lock used for getting/setting Dwarf_Lines. It is a little
unfortunate that lines and files table reading is so intertwined.

I understand why you use the same lock for both.  But it would be good
to document somewhere fields the lock really protects.

I think I am spotting a missed unlock below.

> diff --git a/libdw/dwarf_getsrclines.c b/libdw/dwarf_getsrclines.c
> index da78db67..fb2c431b 100644
> --- a/libdw/dwarf_getsrclines.c
> +++ b/libdw/dwarf_getsrclines.c
> @@ -1197,8 +1197,6 @@ read_srclines (Dwarf *dbg,
>                         + nnewfiles * sizeof (Dwarf_Fileinfo)
>                         + (ndirs + 1) * sizeof (char *),
>                         1);
> -
> -
>        /* Copy prevfiles to newfiles.  */
>        for (size_t n = 0; n < nprevfiles; n++)
>  	newfiles->info[n] = prevfiles->info[n];
> @@ -1442,8 +1440,10 @@ dwarf_getsrclines (Dwarf_Die *cudie, Dwarf_Lines **lines, size_t *nlines)
>        return -1;
>      }
>  
> -  /* Get the information if it is not already known.  */
>    struct Dwarf_CU *const cu = cudie->cu;
> +  mutex_lock (cu->dbg->dwarf_lock);
> +
> +  /* Get the information if it is not already known.  */
>    if (cu->lines == NULL)
>      {
>        /* For split units always pick the lines from the skeleton.  */
> @@ -1464,10 +1464,13 @@ dwarf_getsrclines (Dwarf_Die *cudie, Dwarf_Lines **lines, size_t *nlines)
>  		  *lines = cu->lines;
>  		  *nlines = cu->lines->nlines;
>  		}
> +
> +	      mutex_unlock (cu->dbg->dwarf_lock);
>  	      return res;
>  	    }
>  
>  	  __libdw_seterrno (DWARF_E_NO_DEBUG_LINE);
> +	  mutex_unlock (cu->dbg->dwarf_lock);
>  	  return -1;
>  	}
>  
> @@ -1485,12 +1488,18 @@ dwarf_getsrclines (Dwarf_Die *cudie, Dwarf_Lines **lines, size_t *nlines)
>        Dwarf_Off debug_line_offset;
>        if (__libdw_formptr (stmt_list, IDX_debug_line, DWARF_E_NO_DEBUG_LINE,
>  			   NULL, &debug_line_offset) == NULL)
> -	return -1;
> +	{
> +	  mutex_unlock (cu->dbg->dwarf_lock);
> +	  return -1;
> +	}
>  
>        if (__libdw_getsrclines (cu->dbg, debug_line_offset,
>  			       __libdw_getcompdir (cudie),
>  			       cu->address_size, &cu->lines, &cu->files) < 0)
> -	return -1;
> +	{
> +	  mutex_unlock (cu->dbg->dwarf_lock);
> +	  return -1;
> +	}
>      }
>    else if (cu->lines == (void *) -1l)
>      return -1;

Aren't we still holding the lock here?

> @@ -1498,8 +1507,7 @@ dwarf_getsrclines (Dwarf_Die *cudie, Dwarf_Lines **lines, size_t *nlines)
>    *lines = cu->lines;
>    *nlines = cu->lines->nlines;
>  
> -  // XXX Eventually: unlocking here.
> -
> +  mutex_unlock (cu->dbg->dwarf_lock);
>    return 0;
>  }
>  INTDEF(dwarf_getsrclines)
> -- 
> 2.47.1
>