[I am not subscribed to -arm; please keep the bug number in your followups if you'd like me to see them.] On Tue, Jan 11, 2005 at 11:03:59PM +0000, Phil Blundell wrote: > On Tue, 2005-01-11 at 12:37 -0500, Branden Robinson wrote: > > Here are his remarks, recast a bit from IRC-speak into something more > > conventional. > > > > GCC on ARM is doing something different from every other C compiler I've > > seen. It may not deviate from what the C specification allows, but it > > appears to deviate from common practice. The ARM folks would find code > > would work with fewer problems if they fixed GCC to behave like other C > > compilers do. Having an array of structs of a byte each usually forces > > 16 bit alignment only on other compilers I've seen. > > Jim is correct. This behaviour of the ARM compiler seemed like a good > idea in 1988, but subsequent experience has shown that it was a mistake > to pad structs in this way. > > Changing the default behaviour of the compiler definitely would result > in ABI breakage for some programs. We plan to take care of this, and a > variety of other historical goofs, by switching to the new ARM "EABI". > This change will involve a flag day at some point during the next Debian > release cycle, but will result in better performance (by a factor of > more than 10 for some code) and greater compatibility with other > architectures. After discussing this with Keith Packard on IRC, I'm going to apply this patch with a guard on it: #if defined(__GNUC__) && defined(__arm__) Everyone seems to find the patch esthetically abhorrent, but it also appears to be necessary and unavoidable for ARM users. If someone in the ARM community would task themselves with filing a bug when the ARM EABI happens, and let me (well, the Debian X Strike Force generally) know how I can test for it using the preprocessor, I would appreciate it. -- G. Branden Robinson | No executive devotes much effort to Debian GNU/Linux | proving himself wrong. branden@debian.org | -- Laurence J. Peter http://people.debian.org/~branden/ |
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