[Bug translator/28334] cannot handle offset into register

[scox at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=28334

Stan Cox <scox at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
                 CC|                            |scox at redhat dot com
         Resolution|---                         |FIXED

--- Comment #1 from Stan Cox <scox at redhat dot com> ---
This is due to the x8664 abi which specifies how structures are passed.  The
structure in the example is returned by value, which will return the struct
members in successive registers as specified by the x8664 abi.  In this
particular case members are packed into a single register and systemtap is thus
not able to pry it apart.  Thus the error "cannot handle offset into register"

The abi says:
 The classification of aggregate (structures and arrays) and union types works
as follows:
1. If the size of an object is larger than four eightbytes, or it contains
unaligned
fields, it has class MEMORY

So if the example is changed to be double width; double angle; then the abi
threshold is hit, the struct is passed by reference and systemtap can then
access individual members.

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