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and later versions provide support to prevent the debugged program from stopping
at instructions that are predicated false. The program execution can be stopped by a
software breakpoint, a hardware breakpoint, or an asynchronous signal. In the case of
optimizations such as if-conversion, the predicated false instructions indicate that an
alternate source path is executed. Hence, stopping the program at a predicated false
instruction results in the misleading conclusion that the path corresponding to the
predicated false instruction is executed. To prevent this ambiguity, HP WDB does not
stop at predicated false instructions.
The predicated false instructions are equated to NOPs (No OPeration), because these
instructions do not modify the processor state. The exception to this rule is the use of
certain instructions, such as wtop, wexit, and frcpa, which modify the processor
state even when predicated false. In such cases, the debugger stops at the instructions
irrespective of the predicate value of the instructions. Assembly and low-level
programmers, who require the old behavior of the debugger to stop at the instructions
irrespective of the predicate value of these instructions, can explicitly turn o this feature.
To explicitly turn o this feature, enter the following command at the gdb prompt:
(gdb) set no-predication-handling
The following limitations apply when debugging optimized code:
• Support for high-level loop transformations such as modulo-scheduled loops, or
LNO-optimized loop nests is limited. (This limited support includes all loop
optimizations that are enabled at +O3 and above, and some loop optimizations at
+O2 or -O.)
• Debug support for local aggregates and arrays is limited.
• Complete debug support for inlined subroutines is not available.
• Values that are not at the current code location will be reported as being
unavailable, even if these values can be computed from some other values that
are available.
• Step operations may include occasional "backwards" steps, because of the re-
ordered code during optimization.
• The program stops at asynchronous signal stops even if the reported instruction
is predicated false.
Complete support is available for debugging at the assembly language level. Stepping
by instructions (stepi/nexti) steps as expected and reports the associated source line
numbers for each instruction.
NOTE: The -ipo compilation implies the +noobjdebug option because the -ipo
object files do not store executable code or debug info.
14.30 Debugging with ARIES
The ARIES fast interpreter emulates a complete set of non-privileged PA-RISC
instructions with no user intervention. During interpretation, it monitors the applications
230 HP-UX Configuration-Specific Information