From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kenneth Johansson Date: Mon, 11 Aug 2008 19:21:28 +0200 Subject: [U-Boot] __attribute__((__packed__)) switching to byte-access on ARM In-Reply-To: References: <20080811160630.20B7D248EA@gemini.denx.de> <1218473402.7889.17.camel@localhost.localdomain> Message-ID: <1218475288.7889.23.camel@localhost.localdomain> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: u-boot@lists.denx.de On Mon, 2008-08-11 at 19:00 +0200, Guennadi Liakhovetski wrote: > On Mon, 11 Aug 2008, Kenneth Johansson wrote: > > > > > On Mon, 2008-08-11 at 18:23 +0200, Guennadi Liakhovetski wrote: > > > > > I cannot think of any such examples... I know access-types can be changed > > > on the hardware, say, on a 16-bit bus a 32-bit access can be split into > > > two 16-bit accesses, but I currently cannot think of any examples of the > > > compiler doing such things. But, I think, I can imagine _why_ the compiler > > > might decide to do that - it cannot guarantee, that the structure is > > > 32-bit aligned, so, it is opting for the "safe" variant... So, the > > > question is: is the compiler right and the c-code was wrong, or the other > > > way round? > > > > Both are "right" :). C has a lot of implementation specific stuff that > > can make life interesting. Simple thing like if char is signed or > > unsigned sometimes is really important. > > > > If you have to make sure that the read/write is done in 16 bit the only > > option is to use assembler code. > > I think, properly written mmapped-register access functions like readl() > work perfectly too. > what does the compiler do if you change the code to return *(ulong*)&timers->TCNTO4;