For 10.20, the compilers provide the capabilities to
build with specialized instructions to take advantage of performance
features on PA2.0 systems. The +DA2.0 flag provides these features and
is included in the default flags on PA2.0 systems. One of the
features provided by the compiler is the ability to use 64-bit
registers for arithmetic operations to enhance the performance of the
compiled code.
Summary of Change |
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Only machines with the PA8000 processor chip are affected.
Code generated with the PA2.0 compiler flag set will use 64-bit data
registers, where appropriate, for arithmetic operations. The HP-UX
operating system has been modified to save and restore 64 bits worth
of register information on PA2.0 systems. Applications that implicitly
make use of register information returned by the operating system via
the sigcontext structure will have to be addressed to handle
64-bit data on PA2.0 systems, unless they include no code that has been
generated with the +DA2.0 compiler flag.
Impact |
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Any application that links in any code compiled with the +DA2.0 compiler
flag, including any object modules, shared or archived libraries, and
that has signal handlers that access the register contents in the
sigcontext structure must be prepared to handle 64-bit data registers
unless the code that is compiled with the +DA2.0 flag blocks signals.
If this is not done, it is possible that either program termination or
data corruption may occur, if for example, the application restores
only 32-bits of a 64-bit data register and returns to a section of code
that needs the 64-bit data. Note that this interface of accessing the
machines registers is not part of the HP-UX API and its use is not
encouraged because the information is strictly machine-dependent and cannot
always be made compatible as modifications are made to the underlying
machine architecture.
In addition, code that does access the register contents in the
sigcontext structure, will fail the compile process on a HP-UX 10.20 release
until it has been re-coded to match new names for these registers in
the sigcontext structure. This data was purposefully renamed to alert
users of the coding changes that may be necessary to account for the
larger data.
As this is not a documented interface, the source code modifications
that will need to be made can be found along with the structure
definition in the save_state.h header file.
Performance |
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The 64-bit data registers feature of the PA2.0 compilers is meant to
increase the performance of the applications that can make use of
64-bit arithmetic. Performance benefits will be different depending on
how much the application may be able to take advantage of this feature.
Compatibility |
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Applications that are impacted by this feature may abnormally terminate
or result in data corruption until source code changes are made to the
part of the application that accesses the register information in the
savestate portion of the sigcontext structure. In addition, if the code
that accesses the registers is recompiled on HP-UX 10.20, it will fail the
compile until source code modifications have been made.
Note there is no compatibility issues with this feature if the +DA2.0
compile flag is not used on any of the code contained in the
application, or if the only code compiled with the +DA2.0 flag has
signals blocked, or if the application does not access the register
contents of the sigcontext structure.
As this is not a documented interface, the source code modifications
that will need to be made can be found along with the structure
definition in the save_state.h header file.
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