CVS commit: src/sys/arch

["Cherry G. Mathew" <cherry%netbsd.org@localhost>]

Module Name:    src
Committed By:   cherry
Date:           Sat Dec 22 21:27:22 UTC 2018

Modified Files:
        src/sys/arch/amd64/amd64: cpufunc.S
        src/sys/arch/i386/i386: cpufunc.S i386func.S
        src/sys/arch/xen/x86: xenfunc.c

Log Message:
Introduce a weak alias method of exporting different implementations
of the same API.

For eg: the amd64 native implementation of invlpg() now becomes
amd64_invlpg() with a weak symbol export of invlpg(), while the XEN
implementation becomes xen_invlpg(), also weakly exported as invlpg()

Note that linking in both together without having an override function
named invlpg() would be a mistake, as we have limited control over
which of the two options would emerge as the finally exported invlpg()
resulting in a potential situation where the wrong function is finally
exported. This change avoids this situation.

We should however include an override function invlpg() in that case,
such that it is able to then pass on the call to the appropriate
backing function (amd64_invlpg() in the case of native, and
xen_invlpg() in the case of under XEN virtualisation) at runtime.

This change does not introduce such a function and therefore does not
alter builds to include native as well as XEN implementations in the
same binary. This will be done later, with the introduction of XEN
PVHVM mode, where precisely such a runtime switch is required.

There are no operational changes introduced by this change.


To generate a diff of this commit:
cvs rdiff -u -r1.33 -r1.34 src/sys/arch/amd64/amd64/cpufunc.S
cvs rdiff -u -r1.25 -r1.26 src/sys/arch/i386/i386/cpufunc.S
cvs rdiff -u -r1.18 -r1.19 src/sys/arch/i386/i386/i386func.S
cvs rdiff -u -r1.22 -r1.23 src/sys/arch/xen/x86/xenfunc.c

Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.