Re: bootstrap/5149: gcc-20011217 reads beyond EOF on cygwin

[Neil Booth <neil at daikokuya dot demon dot co dot uk>]

Werner Tuchan wrote:-

> Thats the piece of code that loaded the file, this time its libgcc2.c.
> 
> cppfiles.c
>   388       /* Use mmap if the file is big enough to be worth it (controlled
>   389   by MMAP_THRESHOLD) and if we can safely count on there being
>   390   at least one readable NUL byte after the end of the file's
>   391   contents.  This is true for all tested operating systems when
>   392   the file size is not an exact multiple of the page size.  */
> - 393       if (size / pagesize >= MMAP_THRESHOLD
>   394    && (size % pagesize) != 0)
>   395  {
> - 396    buf = (U_CHAR *) mmap (0, size, PROT_READ, MAP_PRIVATE, inc->fd,
> 0);
> - 397    if (buf == (U_CHAR *)-1)
>   398      goto perror_fail;
> - 399    inc->mapped = 1;
> - 400  }
>   401       else
>   402 #endif

Cool, this is useful, thanks.

> (gdb) x /s buf + 46170
> 0x83a5445a:  "ED_ATEXIT */\n\n#endif /* L_exit */\n"
> 
> (gdb) x /100xb buf + 46170
> 0x83a5445a: 0x45 0x44 0x5f 0x41 0x54 0x45 0x58 0x49
> 0x83a54462: 0x54 0x20 0x2a 0x2f 0x0a 0x0a 0x23 0x65
> 0x83a5446a: 0x6e 0x64 0x69 0x66 0x20 0x2f 0x2a 0x20
> 0x83a54472: 0x4c 0x5f 0x65 0x78 0x69 0x74 0x20 0x2a
> 0x83a5447a: 0x2f 0x0a 0xc0 0xc0 0xc0 0x00 0xc0 0xc0
> 0x83a54482: 0xc0 0x00 0xc0 0xc0 0xc0 0x00 0xc0 0xc0
> 0x83a5448a: 0xc0 0x00 0xc0 0xc0 0xc0 0x00 0xc0 0xc0
> 0x83a54492: 0xc0 0x00 0xc0 0xc0 0xc0 0x00 0xc0 0xc0
> 0x83a5449a: 0xc0 0x00 0x00 0x00 0x00 0x00 0x00 0x00
> 0x83a544a2: 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
> 0x83a544aa: 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
> 0x83a544b2: 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
> 0x83a544ba: 0x00 0x00 0x00 0x00

Weird.  The bytes after EOF are a mixture of NULs and 0xc0.  Is 0xc0
of special significance in Windows?  Is your version of cygwin the
latest?  I recall some talk about mmap bugs in cygwin.

I guess that we have to disable mmap() on cygwin, or at least on
specific versions.  Do you have any better ideas Zack?

Neil.