----- Original Message ----- From: "Corinna Vinschen" <[EMAIL PROTECTED]>
> mmap (MapViewOfFile resp.) alwaus map whole pages. A page is 4096 > bytes long. > > If a file is, say, 8190 bytes, then we have a two page map, size 8192. > So we have two trailing 0 bytes. If getpagesize() returns 4096, gcc can > count that correctly, if getpagesize returns 65536, gcc assumes 57346 > trailing bytes. No problem, gcc only accesses exactly one trailing 0 byte. > > If the file is 8192 bytes long, mmap maps exactly 8192 bytes, no > trailing bytes left. If getpagesize() returns 4096, gcc knows that, > if getpagesize returns 65536, gcc assumes 57344 trailing bytes. > Now it is a problem, since the one trailing 0 byte doesn't exist. > Segmentation fault. Ok. Lets see if I understand: Let m be the size reported by getpagesize. Let f be the size of a file gcc is mmaping. 1) Gcc can't handle a remainder of m divided by f that is greater than <some number between 2 and 57346>. 2) If the remainfer of m divided by f is 0, gcc behaves correctly. 3) If f > m, then gcc assumes that f is m bytes long? Sounds to me like gcc is badly broken. i.e. in your prior example: where m = 4096 if the file is 2048 bytes long, mmap maps exactly 2048 bytes. if m is 4096, gcc assumes there is 2048 trailing bytes. Now it is a problem, since the one trailing 0 byte doesn't exist. Segmentation fault. IOW, I don't see how the 4K vs 64K thing affects this scenario, it seems to be driven purely by the fact the m != 1. Rob -- Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple Bug reporting: http://cygwin.com/bugs.html Documentation: http://cygwin.com/docs.html FAQ: http://cygwin.com/faq/
