From: jonathan@westwood.com (Jonathan Lanier) Subject: I found another compiler bug! 7 May 1997 22:35:58 -0700 Approved: cygnus.gnu-win32@cygnus.com Distribution: cygnus Message-ID: Mime-Version: 1.0 Content-Type: MULTIPART/MIXED; BOUNDARY="-559023410-851401618-863043406=:29829" Original-To: Win32 Mailing List Original-cc: colin@bird.fu.is.saga-u.ac.jp Original-Sender: owner-gnu-win32@cygnus.com This message is in MIME format. The first part should be readable text, while the remaining parts are likely unreadable without MIME-aware tools. Send mail to mime@docserver.cac.washington.edu for more info. ---559023410-851401618-863043406=:29829 Content-Type: TEXT/PLAIN; charset=US-ASCII Attached is an example of a serious bug in the GCC compiler. The gist of it is, if you use packed structures in GCC, and then attempt to use bitfields in those packed structures, the compiler completely miscalculates the offsets for the data in the structure. This example demonstrates a C++ class containing only 2 members. Each one is initialized separately, and the resulting answers printed for each member should be different, but they are not. Removing the __attribute__((packed)) keyword gets rid of the error, but it means you can't pack your structures, which in my case is something I really need to do! Does anyone know if this bug was previously known, or if it exists on other architectures? - Jonathan jonathan@westwood.com ---559023410-851401618-863043406=:29829 Content-Type: TEXT/PLAIN; charset=US-ASCII; name="bits.cpp" Content-Transfer-Encoding: BASE64 Content-ID: Content-Description: I2luY2x1ZGUgPHN0ZGlvLmg+DQ0KDQ0KDQ0KY2xhc3MgQmFkQml0cw0NCnsN DQoJcHVibGljOg0NCgkJQmFkQml0cyh1bnNpZ25lZCBkdW1teSk7DQ0KDQ0K CQl1bnNpZ25lZCBCaXRCcmFpbjoxOw0NCgkJdW5zaWduZWQgRHVtbXk7DQ0K fSBfX2F0dHJpYnV0ZV9fKChwYWNrZWQpKTsNDQoNDQoNDQpCYWRCaXRzOjpC YWRCaXRzKHVuc2lnbmVkIGR1bW15KQ0NCgk6IEJpdEJyYWluKGZhbHNlKSwg RHVtbXkoZHVtbXkpDQ0Kew0NCn0NDQoNDQoNDQppbnQgbWFpbih2b2lkKTsN DQoNDQoNDQppbnQgbWFpbih2b2lkKQ0NCnsNDQoJQmFkQml0cyBNeUJhZEJp dHMoMSk7DQ0KDQ0KCXByaW50ZigiTXlCYWRCaXRzLkJpdEJyYWluIGlzICVk XG4iLCAoaW50KU15QmFkQml0cy5CaXRCcmFpbik7DQ0KCXByaW50ZigiICAg TXlCYWRCaXRzLkR1bW15IGlzICVkXG4iLCAoaW50KU15QmFkQml0cy5EdW1t eSk7DQ0KDQ0KDQ0KCXByaW50ZigiXG4gICAgICBBZGRyZXNzIG9mIE15QmFk Qml0czogMHglbHhcbiIsICh1bnNpZ25lZCBsb25nKSZNeUJhZEJpdHMpOw0N CglwcmludGYoIkFkZHJlc3Mgb2YgTXlCYWRCaXRzLkR1bW15OiAweCVseFxu IiwgKHVuc2lnbmVkIGxvbmcpJk15QmFkQml0cy5EdW1teSk7DQ0KDQ0KCXJl dHVybigwKTsNDQp9DQ0K ---559023410-851401618-863043406=:29829-- - For help on using this list (especially unsubscribing), send a message to "gnu-win32-request@cygnus.com" with one line of text: "help".