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From: "dsmith at redhat dot com" <sourceware-bugzilla@sourceware.org>
To: systemtap@sources.redhat.com
Subject: [Bug runtime/12341] New: deref()/store_deref() variations between arches
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http://sourceware.org/bugzilla/show_bug.cgi?id=12341

           Summary: deref()/store_deref() variations between arches
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: runtime
        AssignedTo: systemtap@sources.redhat.com
        ReportedBy: dsmith@redhat.com


There is a different deref()/store_deref() macro in runtime/loc2c-runtime.h for
each arch.

For i386/x86_64, deref() calls the kernel's __get_user_asm().  store_deref()
calls the kernel's __put_user_asm().

For ia64, deref() calls the kernel's __get_user_size().  store_deref() calls
the kernel's __put_user_size().

For powerpc, deref() calls __stp_get_user_asm(), which is custom powerpc
assembly code (that looks almost identical to the kernel's __get_user_asm()). 
store_deref() calls __stp_put_user_asm(), which is custom powerpc assembly
code.

For s390, deref() calls __stp_get_user_asm(), which is custom s390 assembly. 
store_deref() calls __stp_put_user_asm(), which is custom s390 assembly.

It might be possible for all arches to use the kernel's own routines, instead
of having custom (powerpc/s390) assembly code.  The
__get_user_size()/__put_user_size() routines might be the most attractive
choice (as the ia64 uses), since they know how handle all the different size
combinations.

(If __get_user_size()/__put_user_size() works for the i386, that could
eliminate the need for the i386 special version of kread/kwrite that can handle
64-bit values.)

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