From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Laight Subject: RE: GCC, unaligned access and UB in the Linux kernel Date: Wed, 5 May 2021 10:41:44 +0000 Message-ID: References: Mime-Version: 1.0 Content-Transfer-Encoding: base64 Return-path: In-Reply-To: Content-Language: en-US List-ID: Content-Type: text/plain; charset="us-ascii" To: "'Vladislav K. Valtchev'" , "linux-kernel@vger.kernel.org" , "linux-gcc@vger.kernel.org" RnJvbTogVmxhZGlzbGF2IEsuIFZhbHRjaGV2DQo+IFNlbnQ6IDA0IE1heSAyMDIxIDE5OjA4DQo+ IA0KPiBIaSBldmVyeW9uZSwNCj4gDQo+IEkgbm90aWNlZCB0aGF0IGluIHRoZSBMaW51eCBrZXJu ZWwgd2UgaGF2ZSBhIGRlZmluZSBjYWxsZWQNCj4gQ09ORklHX0hBVkVfRUZGSUNJRU5UX1VOQUxJ R05FRF9BQ0NFU1MgdGhhdCdzIHVzZWQgaW4gYSBmYWlyIGFtb3VudCBvZiBwbGFjZXMNCj4gd2l0 aCB0aGUgZm9sbG93aW5nIHB1cnBvc2U6IHdoZW4gaXQncyBzZXQsIHVuYWxpZ25lZCBhY2Nlc3Mg aXMgc3VwcG9ydGVkIGJ5IHRoZQ0KPiBDUFUgc28gd2UgY2FuIGRvIGl0IGRpcmVjdGx5LCBvdGhl cndpc2UgZmFsbC1iYWNrIHRvIHNvbWUgbG9naWMgd2hlcmUgYSBieXRlIGF0DQo+IHRoZSB0aW1l IGlzIHJlYWQvd3JpdHRlbi4gRm9yIGV4YW1wbGUsIGNoZWNrIHRoZSBpbXBsZW1lbnRhdGlvbiBv Zg0KPiBkb19zdHJuY3B5X2Zyb21fdXNlcigpOg0KPiBodHRwczovL2VsaXhpci5ib290bGluLmNv bS9saW51eC9sYXRlc3Qvc291cmNlL2xpYi9zdHJuY3B5X2Zyb21fdXNlci5jI0wxNQ0KPiANCj4g DQo+IFRoYXQncyBuaWNlIGFuZCBzZWVtcyB0byB3b3JrIHRvZGF5IGFzIGV4cGVjdGVkLCBidXQg dGhlcmUncyBvbmUgcHJvYmxlbToNCj4gdW5hbGlnbmVkIGFjY2VzcyBpcyBVQiBhY2NvcmRpbmcg dG8gdGhlIElTTyBDIHN0YW5kYXJkLCAuLi4NCg0KVGhlIEMgc3RhbmRhcmQgaXNuJ3QgcmVsZXZh bnQuDQoNCi4uLg0KPiANCj4gTWl0aWdhdGlvbnMNCj4gLS0tLS0tLS0tLS0tDQo+IEluIG15IHVu ZGVyc3RhbmRpbmcsIHRoZSBzaW1wbGVzdCB3YXkgdG8gZm9yY2UgR0NDIHRvIGVtaXQgYSBzaW5n bGUgTU9WDQo+IGluc3RydWN0aW9uIHdpdGggdW5hbGlnbmVkIGFjY2Vzcywgd2l0aG91dCByaXNr aW5nIGFueSBraW5kIG9mIFVCLCBpcyB0byB1c2UNCj4gX19idWlsdGluX21lbWNweSgpLiBJdCB3 b3JrcyBncmVhdCwgYnV0IGl0IHJlcXVpcmVzIGZpeGluZyB0aGUgY29kZSBpbiBtYW55DQo+IHBs YWNlcy4gQWxzbywgbWF5YmUgdXNpbmcgZ2V0X3VuYWxpZ25lZCgpL3B1dF91bmFsaWduZWQoKSBp cyB0aGUgcmlnaHQgdGhpbmcgdG8NCj4gZG8/IFRoZSBwcm9ibGVtIGlzIHRoYXQgdGhlIHB1dF91 bmFsaWduZWRfKiBpbmxpbmUgZnVuY3Rpb25zIGRvbid0IHVzZQ0KPiBfX2J1aWx0aW5fbWVtY3B5 KCkgYW5kIGFyZSBkZWZpbmVkIGxpa2U6DQo+IA0KPiAgICBzdGF0aWMgX19hbHdheXNfaW5saW5l IHZvaWQgcHV0X3VuYWxpZ25lZF9sZTMyKHUzMiB2YWwsIHZvaWQgKnApDQo+ICAgIHsNCj4gICAg CSooKF9fbGUzMiAqKXApID0gY3B1X3RvX2xlMzIodmFsKTsNCj4gICAgfQ0KPiANCj4gU28sIHN0 aWxsIFVCLiBUbyBtYWtlIHRoZSBjb21waWxlciBoYXBweSwgbWF5YmUgd2Ugc2hvdWxkIG1ha2Ug dGhlbSB1c2UNCj4gX19idWlsdGluX21lbWNweSgpPw0KDQpUaGF0IGRvZXNuJ3QgaGVscCB5b3Ug YXQgYWxsLg0KSWYgdGhlIGNvbXBpbGVyIGlzIGdpdmVuIGFueSBoaW50IHRoYXQgdGhlIGFkZHJl c3MgaXMgYWxpZ25lZA0KaXQgd2lsbCB1c2UgcG90ZW50aWFsbHkgbWlzYWxpZ25lZCBtZW1vcnkg YWNjZXNzZXMuDQpTbyBpZiB0aGUgYWJvdmUgd2FzOg0KCSooaW50IF9fYXR0cmlidXRlX18oKHBh Y2tlZCkpICopcCA9IHZhbDsNCmFuZCB0aGUgY2FsbGVyIGhhZDoNCglpbnQgKnAgPSBtYXliZV91 bmFsaWduZWQoKTsNCglwdXRfdW5hbGlnbmVkX2xlMzIoMCwgcCk7DQoNClRoZW4gZ2NjIHdpbGwg Z2VuZXJhdGUgYSAzMmJpdCB3cml0ZSBldmVuIG9uIHNwYXJjLg0KX19idWlsdGluX21lbWNweSgp IHdpbGwgZXhwYW5kIHRvIGV4YWN0bHkgdGhlIHNhbWUgMzJiaXQgd3JpdGUuDQoNClRoaXMgaXMg bm90aGluZyBuZXcgLSBhdCBsZWFzdCAyMCB5ZWFycy4NCg0KQmFzaWNhbGx5LCB0aGUgQyBzdGFu ZGFyZCBvbmx5IGFsbG93cyB5b3UgdG8gY2FzdCBhIHBvaW50ZXINCnRvICd2b2lkIConIGFuZCB0 aGVuIGJhY2sgdG8gaXRzIG9yaWdpbmFsIHR5cGUuDQpHQ0MgbWFrZXMgdXNlIG9mIHRoaXMgZm9y IHZhcmlvdXMgb3B0aW1pc2F0aW9ucyBhbmQgd2lsbA0KdHJhY2sgdGhlIGFsaWdubWVudCB0aHJv dWdoICh2b2lkICopIGNhc3RzLg0KDQpJIGJlbGlldmUgdGhhdCwgZXZlbiBmb3IgdGhlIHNpbWQg aW5zdHJ1Y3Rpb25zLCBnY2Mgd2lsbCBwaWNrDQp0aGUgJ21pc2FsaWduIHN1cHBvcnRpbmcnIHZl cnNpb24gaWYgdGhlIGRhdGEgaXMgbWFya2VkDQp3aXRoIHRoZSByZWxldmFudCBhbGlnbm1lbnQu DQoNCk9oIC0gYW5kIHRoZSBsb29wIHZlY3RvcmlzYXRpb24gY29kZSBpcyBhIHBpbGUgb2YgY3Jh cC4NCllvdSBhbG1vc3QgbmV2ZXIgd2FudCBpdCAtIGxvb2sgYXQgdGhlIGNvZGUgaXQgZ2VuZXJh dGVzDQpmb3IgYSBsb29wIHlvdSBnbyByb3VuZCBhIGZldyB0aW1lcy4NCkl0IHlvdSBhcmUgZG9p bmcgMTAwMDAgaXRlcmFjdGlvbnMgeW91J2xsIG5lZWQgdG8gdW5yb2xsDQppdCB5b3Vyc2VsZiB0 byBnZXQgZGVjZW50IHBlcmZvcm1hbmNlLg0KDQoJRGF2aWQNCg0KLQ0KUmVnaXN0ZXJlZCBBZGRy ZXNzIExha2VzaWRlLCBCcmFtbGV5IFJvYWQsIE1vdW50IEZhcm0sIE1pbHRvbiBLZXluZXMsIE1L MSAxUFQsIFVLDQpSZWdpc3RyYXRpb24gTm86IDEzOTczODYgKFdhbGVzKQ0K