On Tue, Jul 31 2018, Michael Felt wrote:
> I hope a I have a "leap forward" > > > On 7/30/2018 11:39 AM, Ævar Arnfjörð Bjarmason wrote: >> Perhaps it's worth taking a step back here and thinking about whether >> this whole thing is unworkable. It was hard enough to get this to work >> on the combination of Linux, *BSD and Solaris, but I suspect we'll run >> into increasingly obscure platforms where this is hard or impossible >> (AIX, HP/UX etc.) > While I still cannot say for HP/UX it does seem there is a potential > solution based on the status for _LITTLE_ENDIAN and _BIG_ENDIAN. At > least, gcc on POWER and xlc on POWER provides one or the other - and my > hope is that gcc on other platforms also provides them. Yeah with GCC this is relatively easy, see https://github.com/cr-marcstevens/sha1collisiondetection/blame/c3e1304/lib/sha1.c#L29-L115 > For "other" compilers that do not provide them - a modification to > CFLAGS to define one or the other should make "make" work. > > Details (note - I am not a programmer, so by definition at least one of > my "macros" will be wrong :) > > AIX and xlc > root@x066:[/]xlc -qshowmacros -E /dev/null | grep -i endi > 1506-297 (S) Unable to open input file null. A file or directory in the > path name does not exist.. > #define __HHW_BIG_ENDIAN__ 1 > #define __BIG_ENDIAN__ 1 > #define __THW_BIG_ENDIAN__ 1 > #define _BIG_ENDIAN 1 > > On SLES12 (le) and xlc > suse12test:~/images/littleEndian/sles # xlc -qshowmacros -dM -E x.c | > grep -i endi > #define _LITTLE_ENDIAN 1 > #define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__ > #define __FLOAT_WORD_ORDER__ __ORDER_LITTLE_ENDIAN__ > #define __LITTLE_ENDIAN__ 1 > #define __ORDER_BIG_ENDIAN__ 4321 > #define __ORDER_LITTLE_ENDIAN__ 1234 > #define __ORDER_PDP_ENDIAN__ 3412 > #define __VEC_ELEMENT_REG_ORDER__ __ORDER_LITTLE_ENDIAN__ > > > Based on what I can see on gcc on POWER and xlc on POWER I think an > approach (simplified) can be: > > #if undefined(_BIG_ENDIAN) && undef(_LITTLE_ENDIAN) > #error "one of _BIG_ENDIAN or _LITTLE_ENDIAN must be defined. Try adding > the correct value to CFLAGS" > #else defined(_BIG_ENDIAN) && defined(_LITTLE_ENDIAN) > #error "Only one of _BIG_ENDIAN and _LITTLE_ENDIAN may be defined, not both" > #endif > > And then logic based on the value set. > This should also make cross-compile possible by unsetting an incorrect > default and setting the correct value. ...the real trick is using these macros outside of GCC / glibc and on older GCC versions. See the github link above, you basically end up with a whitelist of how it looks on different systems / compilers. Sometimes both are defined, sometimes only both etc. It can be done, but as that code shows it's somewhat complex macro soup to get right. > p.s. Is there a setting I need to set somewhere so I receive a copy of > the email sent after it is received by the list. I could send myself a > copy, but I much prefer it comes from the maillist - as verification it > was received. You should get that, but maybe your mailer ignores Message-Ids it already has, but you can go to https://public-inbox.org/git/ and search for the Message-Id or your name to see E-Mails you've sent that made it to the list, e.g.: https://public-inbox.org/git/?q=aixtools%40felt.demon.nl
