HP OpenVMS Systems Documentation

HP OpenVMS System Services Reference Manual

On Alpha and I64 systems, adds a range of demand-zero allocation pages to a process's virtual address space for the execution of the current image. The new pages are added at the virtual address specified by the caller.

This service accepts 64-bit addresses.

Format

SYS$CRETVA_64 region_id_64 ,start_va_64 ,length_64 ,acmode ,flags ,return_va_64 ,return_length_64

C Prototype

int sys$cretva_64 (struct _generic_64 *region_id_64, void *start_va_64, unsigned __int64 length_64, unsigned int acmode, unsigned int flags, void *(*(return_va_64)), unsigned __int64 *return_length_64);

Arguments

region_id_64

OpenVMS usage:	region identifier
type:	quadword (unsigned)
access:	read only
mechanism:	by 32- or 64-bit reference

The region ID associated with the region to create the virtual address range. The file VADEF.H in SYS$STARLET_C.TLB and the $VADEF macro in STARLET.MLB define a symbolic name for each of the three default regions in P0, P1, and P2 space.

The following region IDs are defined:

Symbol	Region
VA$C_P0	Program region
VA$C_P1	Control region
VA$C_P2	64-bit program region

Other region IDs, as returned by the $CREATE_REGION_64 service, can be specified. Also, given a particular virtual address, the region ID for the region it is in can be obtained by calling the $GET_REGION_INFO system service specifying the VA$_REGSUM_BY_VA function.

start_va_64

OpenVMS usage:	address
type:	quadword address
access:	read only
mechanism:	by value

The starting address for the created virtual address range. The specified virtual address must be a CPU-specific page aligned address.

length_64

OpenVMS usage:	byte count
type:	quadword (unsigned)
access:	read only
mechanism:	by value

Length of the virtual address space to be created. The length specified must be a multiple of CPU-specific pages.

acmode

OpenVMS usage:	access_mode
type:	longword (unsigned)
access:	read only
mechanism:	by value

Access mode associated with the call to $CRETVA_64. The access mode determines the owner mode of the pages as well as the read and write protection on the pages. The acmode argument is a longword containing the access mode.

The $PSLDEF macro in STARLET.MLB and the file PSLDEF.H in SYS$STARLET_C.TLB define the following symbols and their values for the four access modes:

Value	Symbolic Name	Access Mode
0	PSL$C_KERNEL	Kernel
1	PSL$C_EXEC	Executive
2	PSL$C_SUPER	Supervisor
3	PSL$C_USER	User

The $CRETVA_64 service uses whichever of the following access modes is least privileged:

• Access mode specified by the acmode argument
• Access mode of the caller

The protection of the pages is read/write for the resultant access mode and those more privileged.

Address space cannot be created within a region that has a create mode associated with it that is more privileged than the caller's mode. The condition value SS$_IVACMODE is returned if the caller is less privileged than the create mode for the region.

flags

OpenVMS usage:	mask_longword
type:	longword (unsigned)
access:	read only
mechanism:	by value

Flag mask controlling the characteristics of the demand-zero pages created. The flags argument is a longword bit vector in which each bit corresponds to a flag. The $VADEF macro and the VADEF.H file define a symbolic name for each flag. You construct the flags argument by performing a logical OR operation on the symbol names for all desired flags.

The following table describes the flag that is valid for the $CRETVA_64 service:

Flag	Description
VA$M_NO_OVERMAP	Pages cannot overmap existing address space. By default, pages can overmap existing address space.

All other bits in the flags argument are reserved for future use by HP and should be specified as 0. The condition value SS$_IVVAFLG is returned if any undefined bits are set.

return_va_64

OpenVMS usage:	address
type:	quadword (unsigned)
access:	write only
mechanism:	by 32- or 64-bit reference

The lowest process virtual address of the created virtual address range. The return_va_64 argument is the 32- or 64-bit virtual address of a naturally aligned quadword into which the service returns the virtual address.

return_length_64

OpenVMS usage:	byte count
type:	quadword (unsigned)
access:	write only
mechanism:	by 32- or 64-bit reference

The length of the virtual address range created. The return_length_64 argument is the 32- or 64-bit virtual address of a naturally aligned quadword into which the service returns the length of the virtual address range in bytes.

Description

The Create Virtual Address Space service is a kernel mode service that can be called from any mode. The service adds a range of demand-zero allocation pages, starting at the virtual address specified by the start_va_64 argument. The pages are added to a process's virtual address space for the execution of the current image. Expansion occurs at the next free available address within the specified region if the range of addresses is beyond the next free available address.

The new pages, which were previously inaccessible to the process, are created as demand-zero pages.

The returned address is always the lowest virtual address in the range of pages created. The returned length is always an unsigned byte count indicating the length of the range of pages created.

Successful return status from $CRETVA means that the specified address space was created of the size specified in the length_64 argument.

If $CRETVA_64 creates pages that already exist, the service deletes those pages if they are not owned by a more privileged access mode than that of the caller. Any such deleted pages are reinitialized as demand-zero pages.

If the condition value SS$_ACCVIO is returned by this service, a value cannot be returned in the memory locations pointed to by the return_va_64 and return_length_64 arguments.

If an address within the specified address range is not within the bounds of the specified region, the condition value SS$_PAGNOTINREG is returned.

If a condition value other than SS$_ACCVIO is returned, the returned address and returned length indicate the pages that were successfully added before the error occurred. If no pages were added, the return_va_64 argument will contain the value --1, and a value cannot be returned in the memory location pointed to by the return_length_64 argument.

Required Privileges

None

Required Quota

The working set quota (WSQUOTA) of the process must be sufficient to accommodate the increased length of the process page table required by the increase in virtual address space.

The process's paging file quota (PGFLQUOTA) must be sufficient to accommodate the increased size of the virtual address space.

Related Services

$CREATE_BUFOBJ_64, $CREATE_REGION_64, $DELETE_REGION_64, $DELTVA_64, $EXPREG_64, $LCKPAG_64, $LKWSET_64, $PURGE_WS, $SETPRT_64, $ULKPAG_64, $ULWSET_64

Condition Values Returned

SS$_NORMAL	The service completed successfully.
SS$_ACCVIO	The return_va_64 or return_length_64 argument cannot be written by the caller.
SS$_EXPGFLQUOTA	The process has exceeded its paging file quota.
SS$_INSFWSL	The process's working set limit is not large enough to accommodate the increased virtual address space.
SS$_IVACMODE	The caller's mode is less privileged than the create mode associated with the region.
SS$_IVREGID	An invalid region ID was specified.
SS$_IVVAFLG	An invalid flag, a reserved flag, or an invalid combination of flags and arguments was specified.
SS$_LEN_NOTPAGMULT	The length_64 argument is not a multiple of CPU-specific pages.
SS$_NOSHPTS	The region ID of a shared page table region was specified.
SS$_PAGNOTINREG	A page in the specified range is not within the specified region.
SS$_PAGOWNVIO	A page in the specified range already exists and cannot be deleted because it is owned by a more privileged access mode than that of the caller.
SS$_REGISFULL	The specified virtual region is full.
SS$_VA_IN_USE	A page in the specified range is already mapped, and the VA$M_NO_OVERLAP flag was set, or the existing underlying page cannot be deleted because it is associated with a buffer object.
SS$_VA_NOTPAGALGN	The start_va_64 argument is not CPU-specific page aligned.

Allows a process to associate (map) a section of its address space with either a specified section of a file (a disk file section) or specified physical addresses represented by page frame numbers (a page frame section). This service also allows the process to create either type of section and to specify that the section be available only to the creating process (private section) or to all processes that map to it (global section).

Format

SYS$CRMPSC [inadr] ,[retadr] ,[acmode] ,[flags] ,[gsdnam] ,[ident] ,[relpag] ,[chan] ,[pagcnt] ,[vbn] ,[prot] ,[pfc]

C Prototype

int sys$crmpsc (struct _va_range *inadr, struct _va_range *retadr, unsigned int acmode, unsigned int flags, void *gsdnam, unsigned int relpag, unsigned short int chan, unsigned int pagcnt, unsigned int vbn, unsigned int prot,unsigned int pfc);

Arguments

inadr

OpenVMS usage:	address_range
type:	longword (unsigned)
access:	read only
mechanism:	by reference

Starting and ending virtual addresses into which the section is to be mapped. The inadr argument is the address of a 2-longword array containing, in order, the starting and ending process virtual addresses. Only the virtual page number portion of each virtual address is used to specify which pages are to be mapped; the low-order byte-within-page bits are ignored for this purpose.

The interpretation of the inadr argument depends on the setting of SEC$M_EXPREG in the flags argument and on whether you are using an Alpha, an I64, or a VAX system. The two system types are discussed separately in this section.

Alpha and I64 System Usage

On Alpha and I64 systems, if you do not set the SEC$M_EXPREG flag, the inadr argument specifies the starting and ending virtual addresses of the region to be mapped. Addresses in system space are not allowed. The addresses must be aligned on CPU-specific pages; no rounding to CPU-specific pages occurs. The lower address of the inadr argument must be on a CPU-specific page boundary and the higher address of the inadr argument must be 1 less than a CPU-specific boundary, thus forming a range, from lowest to highest, of address bytes. You can use the SYI$_PAGE_SIZE item code in the $GETSYI system service to set the inadr argument to the proper values. You do this to avoid programming errors that might arise because of incorrect programming assumptions about page sizes.

If, on the other hand, you do set the SEC$M_EXPREG flag, indicating that the mapping should take place using the first available space in a particular region, the inadr argument is used only to indicate the desired region: the program region (P0) or the control region (P1).

Caution Mapping into the P1 region is generally discouraged, but, if done, must be executed with extreme care. Because the user stack is mapped in P1, it is possible that references to the user stack might inadvertently read or write the pages mapped with $CRMPSC.

When the SEC$M_EXPREG flag is set, the second inadr longword is ignored, while bit 30 (the second most significant bit) of the first inadr longword is used to determine the region of choice. If the bit is clear, P0 is chosen; if the bit is set, P1 is chosen. On Alpha and I64 systems, bit 31 (the most significant bit) of the first inadr longword must be 0. To ensure compatibility between VAX and Alpha or I64 systems when you choose a region, HP recommends that you specify, for the first inadr longword, any virtual address in the desired region.

In general, the inadr argument should be specified; however, it can be omitted to request a special feature: for permanent global sections, you can omit the inadr argument, or specify it as 0, to request that the section be created but not mapped. Such a request will be granted regardless of the setting of the SEC$M_EXPREG flag; however, to ensure compatibility between VAX and Alpha or I64 systems, HP recommends that the SEC$M_EXPREG flag be clear when the inadr argument is omitted.

VAX System Usage

On VAX systems, if you do not set the SEC$M_EXPREG flag, the inadr argument specifies the starting and ending virtual addresses of the region to be mapped. Addresses in system space are not allowed. If the starting and ending virtual addresses are the same, a single page is mapped.

Note If the SEC$M_EXPREG flag is not set, HP recommends that the inadr argument always specify the entire virtual address range, from starting byte address to ending byte address. This ensures compatibility between VAX and Alpha or I64 systems.

If, on the other hand, you do set the SEC$M_EXPREG flag, indicating that the mapping should take place using the first available space in a particular region, the inadr argument is used only to indicate the desired region: the program region (P0) or the control region (P1).

Caution Mapping into the P1 region is generally discouraged, but, if done, must be executed with extreme care. Because the user stack is mapped in P1, it is possible that references to the user stack might inadvertently read or write the pages mapped with $CRMPSC.

When the SEC$M_EXPREG flag is set, the second inadr longword is ignored, while bit 30 (the second most significant bit) of the first inadr longword is used to determine the region of choice. If the bit is clear, P0 is chosen; if the bit is set, P1 is chosen. On VAX systems, bit 31 (the most significant bit) of the first inadr longword is ignored. To ensure compatibility between VAX and Alpha or I64 systems when you choose a region, HP recommends that you specify, for the first inadr longword, any virtual address in the desired region.

In general, the inadr argument should be specified; however, it can be omitted to request a special feature: for permanent global sections, you can omit the inadr argument, or specify it as 0, to request that the section be created but not mapped. You must also ensure that SEC$M_EXPREG is not set in the flags argument. Omitting the inadr argument with SEC$M_EXPREG set is interpreted by VAX systems as a request to map with no region preference. This latter combination of argument settings is strongly discouraged, as the chosen region is indeterminate. To ensure compatibility between VAX and Alpha or I64 systems, HP recommends that the SEC$M_EXPREG flag be clear when the inadr argument is omitted.

retadr

OpenVMS usage:	address_range
type:	longword (unsigned)
access:	write only
mechanism:	by reference--array reference

Starting and ending process virtual addresses into which the section was actually mapped by $CRMPSC. The retadr argument is the address of a 2-longword array containing, in order, the starting and ending process virtual addresses.

On Alpha and I64 systems, the retadr argument returns starting and ending addresses of the usable range of addresses. This might differ from the total amount mapped. The retadr argument is required when the relpag argument is specified. If the section being mapped does not completely fill the last page used to map the section, the retadr argument indicates the highest address that actually maps the section. If the relpag argument is used to specify an offset into the section, the retadr argument reflects the offset.

acmode

OpenVMS usage:	access_mode
type:	longword (unsigned)
access:	read only
mechanism:	by value

Access mode that is to be the owner of the pages created during the mapping. The acmode argument is a longword containing the access mode.

The $PSLDEF macro defines the following symbols for the four access modes:

Symbol	Access Mode
PSL$C_KERNEL	Kernel
PSL$C_EXEC	Executive
PSL$C_SUPER	Supervisor
PSL$C_USER	User

The most privileged access mode used is the access mode of the caller.

flags

OpenVMS usage:	mask_longword
type:	longword (unsigned)
access:	read only
mechanism:	by value

Flag mask specifying the type of section to be created or mapped to, as well as its characteristics. The flags argument is a longword bit vector wherein each bit corresponds to a flag. The $SECDEF macro defines a symbolic name for each flag. You construct the flags argument by performing a logical OR operation on the symbol names for all desired flags.

The following table describes each flag and the default value that it supersedes:

Flag	Description
SEC$M_CRF	Pages are copy-on-reference. By default, pages are shared.
SEC$M_DZRO	Pages are demand-zero pages. By default, they are not zeroed when copied.
SEC$M_EXECUTE	Pages are mapped if the caller has execute access. This flag takes effect only (1) when specified from executive or kernel mode, (2) when the SEC$M_GBL flag is also specified, and (3) when SEC$M_WRT is not specified. By default $CRMPSC performs a read access check against the section.
SEC$M_EXPREG	Pages are mapped into the first available space. By default, pages are mapped into the range specified by the inadr argument. See the inadr argument description for a complete explanation of how to set the SEC$M_EXPREG flag.
SEC$M_GBL	Pages form a global section. The default is private section.
SEC$M_NO_OVERMAP	Pages cannot overmap existing address space. Note that, by default, pages can overmap existing address space.
SEC$M_PAGFIL	Pages form a global page file section. By default, pages form a disk file section. SEC$M_PAGFIL also implies SEC$M_WRT and SEC$M_DZRO.
SEC$M_PERM	Global section is permanent. By default, global sections are temporary.
SEC$M_PFNMAP	Pages form a page frame section. By default, pages form a disk file section. Pages mapped by SEC$M_PFNMAP are not included in or charged against the process's working set; they are always valid. Do not lock these pages in the working set by using $LKWSET; this can result in a machine check if they are in I/O space. ++On Alpha and I64 systems, when the SEC$M_PFNMAP flag is set, the pagcnt and relpag arguments are interpreted in CPU-specific pages, not as pagelets.
SEC$M_SYSGBL	Pages form a system global section. By default, pages form a group global section.
SEC$M_UNCACHED	Flag that must be set when a PFN-mapped section is created if this section is to be treated as uncached memory. Flag is ignored on Alpha systems; it applies only to I64 systems.
SEC$M_WRT	Pages form a read/write section. By default, pages form a read-only section.

gsdnam

For group global sections, the operating system interprets the UIC group as part of the global section name; thus, the names of global sections are unique to UIC groups.

You can specify any name from 1 to 43 characters. All processes mapping to the same global section must specify the same name. Note that the name is case sensitive.

Use of characters valid in logical names is strongly encouraged. Valid values include alphanumeric characters, the dollar sign ($), and the underscore (_). If the name string begins with an underscore (_), the underscore is stripped and the resultant string is considered to be the actual name. Use of the colon (:) is not permitted.

Names are first subject to a logical name translation, after the application of the prefix GBL$ to the name. If the result translates, it is used as the name of the section. If the resulting name does not translate, the name specified by the caller is used as the name of the section.

Additional information on logical name translations and on section name processing is available in the HP OpenVMS Programming Concepts Manual.

ident