Installation guide

5.1.2 New DEC C Default Tuning Could Impact Applications That
Directly Map I/O Space
Applications that directly map and access I/O space with bytes or shorts may
be impacted by the new DEC C compiler.
The default tuning for the DEC C compiler has advanced its focus from
EV4-EV5 architectures to EV56-EV6 architectures. With this change in
tuning, the compiler now generates amask-guarded byte and word instruction
sequences for some loops. The amask guards assure that the byte and word
instructions will not execute on processors that do not support them. Less
efficient instructions will execute instead.
The net result of this change is that users who recompile their applications
with the default tuning may see a slight increase in object code size, a very
slight decrease in performance on EV4-EV5 processors, and a sizable
increase in performance on EV56-EV6 machines.
This change may be disruptive for applications that use special device driver
interfaces that directly map I/O space for devices that do not support 8-bit
and 16-bit access granularity.
If those applications are compiled without –Wf, –static and are run on
EV56-EV6 machines they may corrupt I/O memory. To avoid this
possibility, those applications should be compiled with –tune ev5 which
disables byte/word instruction generation.
5.2 Realtime Programming
The following notes apply to realtime programming.
5.2.1 SA_SIGINFO Not Visible Under Certain Namespace
Conditions
The symbol SA_SIGINFO,defined in sys/signal.h, is not visible under
certain namespace conditions when _POSIX_C_SOURCE is explicitly
defined in the application or on the compile line.
The SA_SIGINFO symbol is visible if you do not explicitly define
_POSIX_C_SOURCE. For most applications, unistd.h provides the
standards definitions needed, including _POSIX_C_SOURCE. As a general
rule, avoid explicitly defining standards macros in your application or on the
compile line. If you do explicitly define _POSIX_C_SOURCE, then
SA_SIGINFO is visible if you also explicitly define _OSF_SOURCE.
5–2 Development Environment Notes