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The Question is: What are the considerations in porting C code from VAX to Alpha OpenVMS over DEC C compiler. Is it a straight recompile? Our application also use DEC's TCP/IP (UCX). Will it influence the port to Alpha? The Answer is :
Documentation on porting from VAX C to DEC C is available in the DEC C
for OpenVMS VAX documentation.
In general, this port is usually little more than recompilation and
relink.
I would recommend porting from VAX C to DEC C on OpenVMS VAX, and then
porting from OpenVMS VAX to OpenVMS Alpha. Both VAX C and DEC C can
be licensed with a current "C" PAK, and both can be installed on the
same system at the same time.
The most common problems with porting the C code from OpenVMS VAX to
OpenVMS Alpha tend to involve:
o resolving various C coding errors and questionable coding
practices.
There are a number of constructs that the older compiler(s)
did not tend to detect.
o the use of the compiler builtins that are not also available
on OpenVMS Alpha
Various pragmas and RTL routines are available.
o assumptions around the structure padding. This tends to come
into play (only) when sharing data structures -- tyically via
network packets or file records -- between OpenVMS VAX and
OpenVMS Alpha systems.
OpenVMS Alpha uses natural alignment for structure members,
while OpenVMS VAX uses byte alignment the fields within a
structure.
One can use the member alignment qualifier and the associated
member alignment pragma to override the defaults.
And sometimes, the use of CC/DECC/STANDARD=VAXC can be useful when
initially porting the code to DEC C.
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