Re: cpp generates wrong #line directives

[Zack Weinberg <zack at wolery dot cumb dot org>]

On Fri, Sep 01, 2000 at 07:18:54PM +0200, Bruno Haible wrote:
> Hi,
> 
> When there are #line directives in a source C files, the #line
> directives emitted by "gcc -E" from this source file can be very
> different from the given ones. As a consequence, functions below that
> point get very wrong debugging information, and gdb displays totally
> useless line numbers.
> 
> The data for this testcase is in
> http://clisp.cons.org/~haible/bug-cpp-20000901.tar.gz
> or
> ftp://clisp.cons.org/pub/lisp/clisp/snapshots/bug-cpp-20000901.tar.gz
> 
> $ gcc -v
> Reading specs from /usr/lib/gcc-lib/i486-suse-linux/2.95.2/specs
> gcc version 2.95.2 19991024 (release)
> $ gcc -E stream.c > stream.i 
> 
> First look at stream.c line 10136. It contains a "#line 9811" statement,
> such that the following "goto read_next_char;" should be remembered as
> line 9818.
> 
> Now look at stream.i line 43508. It contains a "# 9851" statement,
> thus pretending that the following "goto read_next_char;" were in line
> 9852. This is off by 33 lines.

(I hope this is machine-generated code I'm looking at...)

If you look at stream.i you'll see that the last chunk of code before
the goto read_next_char is

            if (ergebnis==0)
              goto empty_buffer;

          }
        }}}}

which corresponds to the code on lines 10057-10062 of stream.c

              goto empty_buffer; /* kein Zeichen verfügbar */
            /* ergebnis=1 -> Zeichen verfügbar */
          }
        }}}}
        #else
        #if defined(UNIX_TERM_TERMIOS) || defined(UNIX_TERM_TERMIO)

and that #if finds its #else on line 10138 of stream.c, right after
the #line you expect to trigger.

#line 9811
}
        #else
        /* Man könnte hier fcntl(stdin_handle,F_SETFL,...|FASYNC) verwenden */
        /* und auf Signal SIGIO warten. Allerdings funktioniert das auf so */
        /* wenigen Systemen (siehe Emacs), dass es sich wohl nicht lohnt. */
        #endif
        #endif
        goto read_next_char;
      }}

So the #line is inside a failed conditional block and is therefore
ignored.  Maybe you need to move it down after the double #endif
there?

zw