User`s guide

How the MACRO Compiler Functions on Different Platforms

2.13 Debugging

• The argument list is homed, and you want to examine an argument that is

less than or equal to the maximum number detected by the compiler (either

by automatic detection or as speciﬁed by MAX_ARGS). If the argument

list is homed, $ARGn symbols always point into the homed argument list.

Subsequent arguments will be in longwords following the last deﬁned $ARGn

symbol.

For example, you can examine arguments beyond the eighth argument in a JSB

routine (where the argument list must be homed in the caller), as follows:

DBG> EX $ARG8 ; highest defined $ARGn

DBG> EX .+4 ; next arg is in next longword

DBG> EX .+4 ; and so on

This example assumes that the caller detected at least 10 arguments when

homing the argument list.

To ﬁnd arguments beyond the last $ARGn symbol in a routine that did not home

the arguments, proceed exactly as in the previous example except substitute EX

.+8 for EX .+4.

2.13.3.2 Additional Arguments That Are Not Easy to Locate

You cannot easily ﬁnd additional arguments if:

• The argument list is not homed, and $ARGn symbols are deﬁned only as high

as $ARG6 on OpenVMS Alpha and $ARG8 on OpenVMS I64. In this case, the

existing $ARGn symbols will either point to registers or to quadword locations

in the stack frame. In both cases, subsequent arguments cannot be examined

by looking at quadword locations beyond the deﬁned $ARGn symbols.

• The argument list is homed, and you want to examine arguments beyond the

number detected by the compiler. The $ARGn symbols point to the longwords

that are stored in the homed argument list. The compiler only moves as many

arguments as it can detect into this list. Examining longwords beyond the

last argument that was homed will result in examining various other stack

context.

The only way to ﬁnd the additional arguments in these cases is to examine the

compiled machine code to determine where the arguments reside. Both of these

problems are eliminated if MAX_ARGS is speciﬁed correctly for the maximum

argument that you want to examine.

2.13.4 Using VAX and Alpha Register Names on OpenVMS I64

For convenience, the MACRO compiler on OpenVMS I64 deﬁnes symbols named

R0, R1, ... R31 to refer to the Itanium registers where those Alpha register values

reside. You can still use the debugger’s names %R0, %R1, ... %R31 to refer to

registers by the native machine’s numbering.

2–34 How the MACRO Compiler Functions on Different Platforms