Is the FreeBSD ABI compatibility policy documented anywhere

[Kostik Belousov]

On Sat, Oct 10, 2009 at 02:11:07PM -0400, Alex Goncharov wrote:
> ,--- You/Dag-Erling (Sat, 10 Oct 2009 19:11:50 +0200) ----*
> | "Simon L. Nielsen" <simon at FreeBSD.org> writes:
> | > It's not entirely that simple.  The ABI on a stable branch like 7.x
> | > should be backward compatible, but there isn't a guarantee of forward
> | > compatibility.  IE, 7.0 binary should be able to run on 7.x, but a 7.2
> | > binary might not run on 7.0.  It should be more or less the same with
> | > the API's.
> | 
> | Correct, but we're getting closer to that now that we have symbol
> | versioning - although we won't reach 100% until we have versioned
> | symbols in *all* libraries, which is currently not the case.  Even then,
> | a developer might break the ABI by mistake, but hopefully we'd catch
> | that before it made it into a release.
> 
> It's important to note that symbol compatibility is not the whole
> thing -- the behaviour on exceptions may be equally important to some
> applications.  E.g. CMUCL code has to handle different ways to notify
> of memory protection failures this way:
> 
>     #if __FreeBSD_version < 700004
>     #define PROTECTION_VIOLATION_SIGNAL SIGBUS
>     #define PROTECTION_VIOLATION_CODE BUS_PAGE_FAULT
>     #else
>     #define PROTECTION_VIOLATION_SIGNAL SIGSEGV
>     #define PROTECTION_VIOLATION_CODE SEGV_ACCERR
>     #endif
> 
> A CMUCL binary built on a pre-7.1 (?) release of FreeBSD, will crash
> almost immediately when run on 7.1 (well, "if memory serves").

This has been an issue for 7.0, and it was explicitely handled, see r174254.
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