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Re: Emacs crashes accidentally

From: Herbert Euler
Subject: Re: Emacs crashes accidentally
Date: Fri, 08 Sep 2006 21:32:24 +0800

From: Richard Stallman <address@hidden>
Reply-To: address@hidden
To: "Herbert Euler" <address@hidden>
CC: address@hidden
Subject: Re: Emacs crashes accidentally
Date: Fri, 08 Sep 2006 07:55:59 -0400

    "SDATA (string)" shall be 0x243d8ac, but value of the first argument
    (PTR) of STROUT is 0x2469648.  This is the reason why Emacs

    But, why this happened?  Memory leak?

I don't see how a memory leak could possibly have such an effect.

Please examine the value of printcharfun and figure out what Lisp
object it is.  That way we can tell what path the code took through
strout.  And what is the value of `i' in strout's frame?

strout increments PTR as it runs.  Maybe it has incremented PTR too

Or maybe message_dolog somehow clobbered the stack and altered PTR.

Basically I am as puzzled as you are.
We need more facts.

(print.c, version, function STROUT)

static void
strout (ptr, size, size_byte, printcharfun, multibyte)
    char *ptr;
    int size, size_byte;
    Lisp_Object printcharfun;
    int multibyte;

[ The value of SIZE is 27, so SIZE_BYTE is not reset. ]

 if (size < 0)
   size_byte = size = strlen (ptr);

 the third branch gets executed. ]

 if (NILP (printcharfun))
     if (print_buffer_pos_byte + size_byte > print_buffer_size)
         print_buffer_size = print_buffer_size * 2 + size_byte;
         print_buffer = (char *) xrealloc (print_buffer,
     bcopy (ptr, print_buffer + print_buffer_pos_byte, size_byte);
     print_buffer_pos += size;
     print_buffer_pos_byte += size_byte;

     if (max_print)
       print_chars += size;
#endif /* MAX_PRINT_CHARS */
 else if (noninteractive && EQ (printcharfun, Qt))
     fwrite (ptr, 1, size_byte, stdout);
     noninteractive_need_newline = 1;

[ This branch gets executed. ]

 else if (EQ (printcharfun, Qt))
     /* Output to echo area.  We're trying to avoid a little overhead
        here, that's the reason we don't call printchar to do the
        job.  */
     int i;

 I don't think I can remember whether the buffer I typed z's
 contains multibyte characters. ]

     int multibyte_p
       = !NILP (current_buffer->enable_multibyte_characters);

[ I assume SETUP_ECHO_AREA_FOR_PRINTING behaves well
 so I didn't trace into it. ]

     setup_echo_area_for_printing (multibyte_p);

[ I see MESSAGE_DOLOG is in xdisp.c, but I compiled Emacs
 without X.  What's the behavior here?  Since MESSAGE_DOLOG
 is very long, I didn't post the tracing.  Btw, Vmemory_full is
 'NIL and Vmessage_log_max is 400. ]

     message_dolog (ptr, size_byte, 0, multibyte_p);

[ Both SIZE and SIZE_BYTE are 27. ]

     if (size == size_byte)

[ gdb shows that crashing happened on INSERT_CHAR.
 While the value of I is 26, so iteration was not finished.
 The value of PTR is 0x2469649, but PRINT_STRINT
 calls STROUT with (I think) 0x243d8ac, so even the
 starting address is not valid. ]

         for (i = 0; i < size; ++i)
           insert_char ((unsigned char )*ptr++);

This is what I can know now from the .core file.  Andreas
Schwab told to find out whether GC was called, but I
don't know how.

Guanpeng Xu

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