Dear Wolfgang, 2009/1/28 Wolfgang Denk <w...@denx.de>: > Dear Luigi Mantellini, > > In message <b73e93990901281416k766b2bf3qc6429f77545f9...@mail.gmail.com> you > wrote: >> >> I think that an audit of the code is important to understand if we >> have a problem (or not) and how large is the problem. > > We (i. e. all of us except you) do not have a problem.
my question is: how can you be sure on this? I haven't used strange compilers or strange CFLAGS.. I just do "make" on a supported target (qemu_mips). I haven't any problem to correct my local source tree. I ask myself why gcc offers a packed atribute, ms-vc offers pragma packed, ... > >> My compiler is not broken... > > Well, YMMV... > the behavior is clear: in my environment, the default choice is to align fields on 32bit for speed reasons... and I like this by default for my applications. I can ignore the problem using options like -Os (I will try tomorrow) or -fpack-struct or other global mechanisms or, pay attention on structures definitions to be sure that the structure size is compiler and cflags independent. >> cassini linux # find -name \*.c -o -name \*.h |xargs grep attribute | >> grep packed | wc -l >> 3153 >> >> I see a lot of packed structs... > > > >> > Here is for example a copy of /usr/include/netinet/ip.h : > ... >> This doesn't say anything regarding how kernel guys have resolved the >> problem (if they are solved...). Checking the kernel headers a lot > > This is not a kernel header. This is one of the standard user space > network headers, and a pretty central one. Feel free to check any > others. > I see. I would like to understand why this structure is optimization-prof. I will study tomorrow... >> I think that "struct packing" needs to be understood and a global > > I agree on this. This definitely needs to be understood. > > Hm... I think I understand it, and it works for me :-) > iso C doensn't require packing by default of the structures. To assume that a structure is packed by default is not a good assumption. All compilers offer directives to control the behavior of packing... I believe that there is a reason... >> mechanism should be used (like -fpack-struct option always defined or >> a style guideline that requires a tag for each structs). From my point > > I think this is not needed. Please read the docuemntation about > alignment and padding. It is pretty clear. which documentation should I read? iso c documents? gcc manuals? I haven't found anything that opposes my affirmations. I want underline that the structures (IP_t, ... ) don't have field across the word-machine boundary... but this doesn't exclude an "memory-access" optimization. Kindly, can you give me any good links? Anyway, I don't want to talk about philosophy. I just noticed an anomaly and I wanted to share with the ML. my 2LireItaliane best regards, luigi > > Best regards, > > Wolfgang Denk > > -- > DENX Software Engineering GmbH, MD: Wolfgang Denk & Detlev Zundel > HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany > Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: w...@denx.de > "And it should be the law: If you use the word `paradigm' without > knowing what the dictionary says it means, you go to jail. No > exceptions." - David Jones @ Megatest Corporation > -- Luigi 'Comio' Mantellini R&D - Software Industrie Dial Face S.p.A. Via Canzo, 4 20068 Peschiera Borromeo (MI), Italy Tel.: +39 02 5167 2813 Fax: +39 02 5167 2459 web: www.idf-hit.com mail: luigi.mantell...@idf-hit.com _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
