cvs commit: src/include string.h src/lib/libc/string Makefile.inc memchr.3 memrchr.c src/sys/sys param.h

[Alexander Kabaev]

On Tue, 27 May 2008 20:04:28 +0000 (UTC)
Xin LI <delphij at FreeBSD.org> wrote:

> delphij     2008-05-27 20:04:27 UTC
> 
>   FreeBSD src repository
> 
>   Modified files:        (Branch: RELENG_6)
>     include              string.h 
>     lib/libc/string      Makefile.inc memchr.3 
>     sys/sys              param.h 
>   Added files:           (Branch: RELENG_6)
>     lib/libc/string      memrchr.c 
>   Log:
>   MFC: Add memrchr(3).
>   
>   Obtained from:  OpenBSD
>   
>   Revision    Changes    Path
>   1.21.2.2    +1 -0      src/include/string.h
>   1.34.8.2    +2 -1      src/lib/libc/string/Makefile.inc
>   1.7.14.3    +28 -3     src/lib/libc/string/memchr.3
>   1.1.4.1     +40 -0     src/lib/libc/string/memrchr.c (new)
> http://cvsweb.FreeBSD.org/src/lib/libc/string/memrchr.c?rev=1.1.4.1&content-type=text/plain
>   1.244.2.37  +1 -1      src/sys/sys/param.h
> 
> http://cvsweb.FreeBSD.org/src/include/string.h.diff?r1=1.21.2.1&r2=1.21.2.2
> http://cvsweb.FreeBSD.org/src/lib/libc/string/Makefile.inc.diff?r1=1.34.8.1&r2=1.34.8.2
> http://cvsweb.FreeBSD.org/src/lib/libc/string/memchr.3.diff?r1=1.7.14.2&r2=1.7.14.3
> http://cvsweb.FreeBSD.org/src/sys/sys/param.h.diff?r1=1.244.2.36&r2=1.244.2.37


There are two levels of symbol versions checking: 

1. Up-front checking of version name.
When binary starts, rtld checks that all versions it was compiled
against are provided by the dynamically loaded libraries. I.e. if
libc.so.7:FBSD_1.1 is recorded as a requirement in binary and given
libc.so.7 does not have that version, the binary execution is
terminated right on the spot.

The assumption here is that if version FOO is claimed to be provided by
the library then _all_ symbols at FOO binary might need are present. This
is the level of symbol versions checking Solaris provides. Linux goes a
bit further:

2. Per-symbol versions.

In addition to the above, ld encodes required version of each undefined
symbol in a binary and uses (name, version) pair to resolve undefined
references as opposed to using only the symbol name. This allows for
several versions of the same symbol to exist within the binary, i.e.
something like read at FOO1 and read at FOO2 are now possible.

Your changes broke assumption in 1. To do it 100% correctly, we probably
need to introduce a side version for memchr, something like
memrchr@@FBSD_1.0a in stable branch and provide a compatibility
alias memrchr at FBSD_1.0a for it in -current at the same time.

libc.so.7 from RELENG_7 will  have:

memrchr@@FBSD_1.0a

libc.so.7 from -current then will  have:

memrchr@@FBSD_1.1
memrchr at FBSD_1.0a -> memrchr@@FBSD_1.1

--
Alexander Kabaev
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