Updated: 11 December 1998

Porting VAX MACRO Code to OpenVMS Alpha

Disables compiler features over a range of source code.

Format

.DISABLE argument-list

Parameters

argument-list

You can use one or more of the symbolic arguments listed in the following table:

Option	Description
DEBUG	Excludes local symbol table information in the object file for use with the debugger.
FLAGGING	Deactivates compiler flagging.
GLOBAL	Disables the assumption that undefined symbols are external symbols.
OVERFLOW	Deactivates production of overflow trap code for the following opcodes: ADDx, ADWC, INCx, ADAWI, SUBx, SBWC, DECx, MNEGx, MULx, CVTxy (where x is greater than y, for example CVTLB), AOBxx, ACBL, and SOBxx.
QUADWORD	Disables support for quadword literal expressions.
SUPPRESSION	Stops the listing of unreferenced symbols in the symbol table.
TRACEBACK	Stops providing traceback information to the debugger.

Enables compiler features over a range of source code.

Format

.ENABLE argument-list

Parameters

argument-list

You can use one or more of the symbolic arguments listed in the following table:

Option	Description
DEBUG 1	Includes local symbol table information in the object file for use with the debugger.
FLAGGING	Activates compiler flagging.
GLOBAL	Assumes undefined symbols are external symbols.
OVERFLOW	Activates production of overflow trap code for the following opcodes: ADDx, ADWC, INCx, ADAWI, SUBx, SBWC, DECx, MNEGx, MULx, CVTxy (where x is greater than y, for example CVTLB), AOBxx, ACBL, and SOBxx.
QUADWORD	Provides support for quadword literal expressions.
SUPPRESSION	Provides a listing of unreferenced symbols in the symbol table.
TRACEBACK 2	Provides traceback information to the debugger.

Declares the entry point of an exception service routine to the compiler.

Format

.EXCEPTION_ENTRY [,stack_base]

Parameters

preserve=<>

Register set that forces the compiler to save and restore across the routine call the contents of registers. By default, the compiler saves at routine entry and restores at routine exit the full 64-bit contents of any register that is modified by a routine.

In the case of an .EXCEPTION_ENTRY routine, exception dispatching saves R2 through R7 on the stack (along with the PC and PSL) and the values of these registers are restored by the REI instruction executed by the routine itself. Other registers, if used, are saved in code generated by the compiler, and all other registers are saved if the routine issues a CALL or JSB instruction.

stack_base

Register into which the stack pointer (SP) value is moved at routine entry. At exception entry points, exception dispatching pushes onto the stack registers R2 through R7, the PC, and the PSL. Note that the Alpha counterpart for the VAX register known as the PSL is the processor status (PS) register. The value returned to the register specified in the stack_base helps an exception service routine locate the values of these registers.

You can use the macro $INTSTKDEF in SYS$LIBRARY:LIB.MLB to define symbols for the area on the stack where R2-R7, the PC, and the PSL are stored. The symbols are:

• INTSTK$Q_R2
• INTSTK$Q_R3
• INTSTK$Q_R4
• INTSTK$Q_R5
• INTSTK$Q_R6
• INTSTK$Q_R7
• INTSTK$Q_PC
• INTSTK$Q_PS

You can then use these symbols in the exception routine, as offsets to the stack_base value. By using the appropriate symbolic offset with the stack_base value, the exception routine can access the saved contents of any of these registers. For example, the exception routine could examine the PSL to see what access mode was in effect when the exception was taken.

Description

The .EXCEPTION_ENTRY directive indicates the entry point of an exception service routine. At routine entry, R3 must contain the address of the procedure descriptor. The routine must exit with an REI instruction.

You should declare with the .EXCEPTION_ENTRY directive all of the following interrupt service routines:

• Interval clock
• Interprocessor interrupt
• System/processor correctable error
• Power failure
• System/processor machine abort
• Software interrupt

Declares a global label in a routine that is not an entry point to the routine.

Format

Label: .GLOBAL_LABEL

There are no parameters for this directive.

Description

The .GLOBAL_LABEL directive declares a global label within a routine that is not a routine entry point. Unless declared with .GLOBAL_LABEL, global labels in code (specified with "::") are assumed to be entry point labels, which require declaration. If they are not declared, they are flagged as errors.

The compiler also allows the address of a global label to be stored (for instance, by means of PUSHAL instruction). (The compiler flags as an error any attempt to store a label that has not been declared as a global label or an entry point.)

By using the .GLOBAL_LABEL directive, the user is acknowledging that the stored code address will not be the target of a CALL or JSB instruction. Global labels must appear inside routine boundaries.

Labels declared with the .GLOBAL_LABEL directive can be used as the newpc argument in calls to the $UNWIND (Unwind Call Stack) system service because it allows the address of the label to be stored.

However, there is no provision in the compiler to automatically adjust the stack pointer at such labels to remove arguments passed on the stack or compensate for stack alignment. If the call stack is unwound back to an alternate PC in the calling routine, the stack may still contain arguments and alignment bytes, and any stack-based references that expect this adjustment to the caller's original stack depth (which happened automatically on VAX) will be incorrect.

Code that contains labels declared with this directive that are to be used as alternate PC targets for $UNWIND must be examined carefully to ensure correct behavior, with particular emphasis on any references based on the stack pointer.

Declares the entry point of a JSB routine to the compiler. This entry declaration will save and restore the full 64 bits of any registers (except R0 and R1) that are modified by the routine and are not declared as scratch or output. See also .JSB32_ENTRY.

Format

.JSB_ENTRY [input] [,output] [,scratch] [,preserve]

Parameters

input=<>

Register set that indicates those registers from which the routine receives input values.

This register set informs the compiler that the registers specified have meaningful values at routine entry and are unavailable for use as temporary registers even before the first compiler-detected use of the registers. Specifying registers in this register set affects compiler temporary register usage in two cases:

• If you are using the VAXREGS optimization switch. This optimization allows the compiler to use as temporary registers any of the VAX registers which are not explicitly being used by the VAX MACRO code.
• If you are explicitly using any of the Alpha registers (R13 and above).

In either of these cases, if you do not specify a register that is being used as input in the input argument, the compiler may use the register as a temporary register, corrupting the input value.

This register set has no effect on the compiler's default register preservation behavior. If you are not using the VAXREGS optimization switch or any of the Alpha registers, the input mask is used only to document your routine.

output=<>

Register set that indicates those registers to which the routine assigns values that are returned to the routine's caller. Registers included in this register set are not saved and restored by the compiler, even if they are modified by the routine.

This register set also informs the compiler that the registers specified have meaningful values at routine exit and are unavailable for use as temporary registers even after the last compiler-detected use of the registers. Specifying registers in this register set affects compiler temporary register usage in two cases:

• If you are using the VAXREGS optimization switch. This optimization allows the compiler to use as temporary registers any of the VAX registers which are not explicitly being used by the VAX MACRO code.
• If you are explicitly using any of the Alpha registers (R13 and above).

In either of these cases, if you do not specify a register that is being used as output in the output argument, the compiler may use the register as a temporary register, corrupting the output value.

scratch=<>

Register set that indicates registers that are used within the routine but which should not be saved and restored at routine entry and exit. The caller of the routine does not expect to receive output values nor does it expect the registers to be preserved. Registers included in this register set are not saved and restored by the compiler, even if they are modified by the routine.

The compiler may use registers R13 and above as temporary registers if they are unused in the routine source code. Because R13 through R15 must be preserved, if modified, according to the OpenVMS Alpha calling standard, the compiler preserves those registers if it uses them.

However, if they appear in the scratch register set declaration, the compiler will not preserve them if it uses them as temporary registers. As a result, these registers may be scratched at routine exit, even if they were not used in the routine source but are in the scratch set. If the VAXREGS optimization is used, this applies to registers R2 through R12, as well.

preserve=<>

Register set that indicates those registers that should be preserved over the routine call. This should include only those registers that are modified and whose full 64-bit contents should be saved and restored.

This register set causes registers to be preserved whether or not they would have been preserved automatically by the compiler. Note that because R0 and R1 are scratch registers, by calling standard definition, the compiler never saves and restores them unless you specify them in this register set.

This register set overrides the output and scratch register sets. If you specify a register both in the preserve register set and in the output or scratch register sets, the compiler will report the following warning:

%AMAC-W-REGDECCON, register declaration conflict in routine A

Declares the entry point of a JSB routine to the compiler. This directive does not preserve any VAX register values (R2 through R12) unless the PRESERVE parameter is specified. The routine itself may save and restore registers by pushing them on the stack, but this will not preserve the upper 32 bits of the registers. See also .JSB_ENTRY.

Warning The .JSB32_ENTRY directive can be a great time-saver if you are sure that you can use it. If you use .JSB32_ENTRY in a situation where the upper 32 bits of a register are being used, it may cause very obscure and difficult-to-track bugs by corrupting a 64-bit value that may be several calling levels above the offending routine. .JSB32_ENTRY should never be used in an AST routine, condition handler, or any other code that can be executed asynchronously.

Format

.JSB32_ENTRY [input] [,output] [,scratch] [,preserve]

Parameters

input=<>

Register set that indicates those registers from which the routine receives input values.

For the .JSB32_ENTRY directive, this register set is used only to document your code.

output=<>

Register set that indicates those registers to which the routine assigns values that are returned to the routine's caller.

For the .JSB32_ENTRY directive, this register set is used only to document your code.

scratch=<>

Register set that indicates registers that are used within the routine but which should not be saved and restored at routine entry and exit. The caller of the routine does not expect to receive output values nor does it expect the registers to be preserved.

The scratch argument also pertains to the compiler's temporary register usage. The compiler may use registers R13 and above as temporary registers if they are unused in the routine source code. Because R13 through R15 must be preserved, if modified, according to the OpenVMS Alpha calling standard, the compiler preserves those registers if it uses them.

However, if they appear in the scratch register set declaration, the compiler will not preserve them if it uses them as temporary registers. As a result, these registers may be scratched at routine exit, even if they were not used in the routine source but are in the scratch set.

Because R2 through R12 are not preserved by default, their inclusion in the scratch is for documentation purposes only.

preserve=<>

Register set that indicates those registers that should be preserved over the routine call. This should include only those registers that are modified and whose full 64-bit contents should be saved and restored.

This register set causes registers to be preserved by the compiler. By default, no registers are preserved by the .JSB32_ENTRY directive.

This register set overrides the output and scratch register sets. If you specify a register both in the preserve register set and in the output or scratch register sets, the compiler will report the warning:

%AMAC-W-REGDECCON, register declaration conflict in routine A

Description

The .JSB32_ENTRY directive is an alternative way of declaring a JSB entry point. It is designed to streamline the declaration of VAX MACRO routines that operate within a well-defined, bounded application environment, such as that of a single application or a self-contained subsystem. For any routine declared with the .JSB32_ENTRY directive, the compiler does not automatically save or restore any VAX registers (R2 through R12), therefore leaving the current 32-bit operation untouched. When you use the .JSB32_ENTRY directive to declare a JSB entry point, you are responsible for declaring and saving registers which must be preserved.

If the externally visible entry points of a subsystem can be called from the 64-bit environment, those entry points should not be declared with .JSB32_ENTRY. Instead, .JSB_ENTRY (or .CALL_ENTRY) should be used so that the full 64-bit register values are saved, if necessary.

Allows the name of the linkage section psect to be changed.

Format

.LINKAGE_PSECT program-section-name

Parameters

program_section_name

Name of the program section. The name can contain up to 31 characters, including any alphanumeric character and the special characters underline (_), dollar sign ($), and period (.).

Description

The .LINKAGE_PSECT directive allows you to locate a routine's linkage section by reference to other psects within the routine. This facilitates such operations as locking code within memory (see Section 3.10) and forcing code location. An example of forcing code location is to explicitly place the psect in the image created by the linker, using linker options. This would let you use adjacent psects to find their bounds.

You can use the .LINKAGE_PSECT directive multiple times within a single source module to set different linkage sections for different routines. However, note that a routine's linkage section remains the same for the entire routine. The name of the routine's linkage section is the one specified in the last .LINKAGE_PSECT directive before the routine's entry point directive.

The compiler reports a fatal error if different linkage sections are specified for routines that share code paths.

The .LINKAGE_PSECT directive sets the psect attributes to be the same as the default linkage psect $LINKAGE. The attributes are the same as the normal psect default attributes except the linkage psect is set NOEXE NOWRT.

You can change the linkage section psect attributes using the .PSECT directive after declaring the psect with .LINKAGE_PSECT.

Example

      .LINKAGE_PSECT LINK_001 
      .PSECT LINK_000 
LS_START: 
      .PSECT LINK_002 
LS_END: 
      

This code allows a program to use LS_START and LS_END in computations to determine the location and size of the linkage section (LINK_001) of the routine.

Directs the compiler to generate special Alpha assembly code for VAX MACRO instructions, within portions of the source module, that rely on VAX guarantees of operation atomicity or granularity.

Format

.[NO]PRESERVE argument-list

Parameters

argument-list

One or more of the symbolic arguments listed in the following table:

Option	Description
GRANULARITY	Preserves the rules of VAX granularity of writes. Specifying .PRESERVE GRANULARITY causes the compiler to use Alpha Load-locked and Store-conditional instruction sequences in code it generates for VAX instructions that perform byte, word, or unaligned longword writes.
ATOMICITY	Preserves atomicity of VAX modify operations. Specifying .PRESERVE ATOMICITY causes the compiler to use Load-locked and Store-conditional instruction sequences in code it generates for instructions with modify operands.

Description

The .PRESERVE and .NOPRESERVE directives cause the compiler to generate special Alpha assembly code for VAX MACRO instructions, within portions of the source module, that rely on VAX guarantees of operation atomicity or granularity (see Section 2.10).

Use of .PRESERVE or .NOPRESERVE without specifying GRANULARITY or ATOMICITY will affect both options. When preservation of both granularity and atomicity is enabled, and the compiler encounters a VAX coding construct that requires both granularity and atomicity guarantees, it enforces atomicity over granularity.

Alternatively, you can use the /PRESERVE and /NOPRESERVE compiler qualifiers to affect the atomicity and granularity in generated code throughout an entire MACRO source module.

Atomicity is guaranteed for multiprocessing systems as well as uniprocessing systems when you specify .PRESERVE ATOMICITY.

When the .PRESERVE directive is present, you can use the /RETRY_COUNT qualifier on the command line to control the number of times the compiler-generated code retries a granular or atomic update.

Warning If .PRESERVE ATOMICITY is turned on, any unaligned data references will result in a fatal reserved operand fault. See Section 2.10.5. If .PRESERVE GRANULARITY is turned on, unaligned word references to addresses assumed aligned will also cause a fatal reserved operand fault.

Example

INCW 1(R0) 
      

This instruction, when compiled with .PRESERVE GRANULARITY, retries the insertion of the new word value, if it is interrupted. However, when compiled with .PRESERVE ATOMICITY, it will also refetch the initial value and increment it, if interrupted. If both options are specified, it will do the latter.

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