DosAllocMem: Difference between revisions
mNo edit summary |
|||
| (2 intermediate revisions by the same user not shown) | |||
| Line 1: | Line 1: | ||
DosAllocMem is used to allocate a private memory object, within the boundaries of the virtual-address space. | DosAllocMem is used to allocate a private memory object, within the boundaries of the virtual-address space. | ||
== Syntax == | |||
DosAllocMem( ''pBaseAddress'', ''ulObjectSize'', ''ulAllocationFlags'' ) | DosAllocMem( ''pBaseAddress'', ''ulObjectSize'', ''ulAllocationFlags'' ) | ||
=== Parameters === | === Parameters === | ||
;PPVOID ''pBaseAddress'' (output):This is a pointer to the variable which will | ;PPVOID ''pBaseAddress'' (output):This is a pointer to the variable which will receive the base address of the allocated private memory object. | ||
;ULONG ''ulObjectSize'' (input):The size in bytes of the memory block you want to allocate. This will, by the system, be rounded up to the next page-size boundary. | ;ULONG ''ulObjectSize'' (input):The size in bytes of the memory block you want to allocate. This will, by the system, be rounded up to the next page-size boundary. | ||
;ULONG ''ulAllocationFlags'' (input):Flags used to describe allocation attributes, as well as access protection of the private memory block. | ;ULONG ''ulAllocationFlags'' (input):Flags used to describe allocation attributes, as well as access protection of the private memory block. | ||
| Line 31: | Line 31: | ||
=== Access protection === | === Access protection === | ||
:'''PAG_EXECUTE''' (0x00000004) tells the system that 'execute access' to the | :'''PAG_EXECUTE''' (0x00000004) tells the system that 'execute access' to the committed pages is desired in the memory block. | ||
:'''PAG_READ''' (0x00000001) tells the system that 'read access' is desired. | :'''PAG_READ''' (0x00000001) tells the system that 'read access' is desired. | ||
:'''PAG_WRITE''' (0x00000002) tells the system that 'write access' is desired. | :'''PAG_WRITE''' (0x00000002) tells the system that 'write access' is desired. | ||
:'''PAG_GUARD''' (0x00000008) tells the system that an access to the committed pages should cause a guard page exception to be raised. | :'''PAG_GUARD''' (0x00000008) tells the system that an access to the committed pages should cause a guard page exception to be raised. | ||
At least one of '''PAG_EXECUTE''', '''PAG_WRITE''' or '''PAG_READ''' must be set. | At least one of '''PAG_EXECUTE''', '''PAG_WRITE''' or '''PAG_READ''' must be set. | ||
| Line 41: | Line 40: | ||
APIRET rc | APIRET rc | ||
The following values can be returned: | The following values can be returned: | ||
*0 NO_ERROR | |||
*8 ERROR_NOT_ENOUGH_MEMORY | |||
*87 ERROR_INVALID_PARAMETER | |||
*95 ERROR_INTERRUPT | |||
=== Sample Code === | === Sample Code === | ||
| Line 64: | Line 54: | ||
ULONG ObjectSize; /* The requested size of the memory block */ | ULONG ObjectSize; /* The requested size of the memory block */ | ||
ULONG AllocationFlags; /* Flags */ | ULONG AllocationFlags; /* Flags */ | ||
APIRET rc; /* Will | APIRET rc; /* Will receive the return code */ | ||
ObjectSize = 9000; /* Asking for 9000 bytes, this will */ | ObjectSize = 9000; /* Asking for 9000 bytes, this will */ | ||
Latest revision as of 23:52, 27 November 2019
DosAllocMem is used to allocate a private memory object, within the boundaries of the virtual-address space.
Syntax
DosAllocMem( pBaseAddress, ulObjectSize, ulAllocationFlags )
Parameters
- PPVOID pBaseAddress (output)
- This is a pointer to the variable which will receive the base address of the allocated private memory object.
- ULONG ulObjectSize (input)
- The size in bytes of the memory block you want to allocate. This will, by the system, be rounded up to the next page-size boundary.
- ULONG ulAllocationFlags (input)
- Flags used to describe allocation attributes, as well as access protection of the private memory block.
Allocation attributes
- PAG_COMMIT (0x00000010) makes all private memory blocks initially committed.
- OBJ_TILE (0x00000040) forces the memory block to be allocated in the first 512MB of virtual-address space. Mapping the memory block is done with the 16-bit selectors. The following table shows how a 32-bit memory block is mapped using 16-bit selectors.
| 32bit Offset | 16bit alias selectors |
| BaseAddress+000KB | Sel |
| BaseAddress+064KB | Sel + HugeInc |
| BaseAddress+128KB | Sel + HugeInc * 2 |
| ... | ... |
HugeInc is the same huge increment that is used by DosAllocHuge.
Access protection
- PAG_EXECUTE (0x00000004) tells the system that 'execute access' to the committed pages is desired in the memory block.
- PAG_READ (0x00000001) tells the system that 'read access' is desired.
- PAG_WRITE (0x00000002) tells the system that 'write access' is desired.
- PAG_GUARD (0x00000008) tells the system that an access to the committed pages should cause a guard page exception to be raised.
At least one of PAG_EXECUTE, PAG_WRITE or PAG_READ must be set.
Returns
APIRET rc
The following values can be returned:
- 0 NO_ERROR
- 8 ERROR_NOT_ENOUGH_MEMORY
- 87 ERROR_INVALID_PARAMETER
- 95 ERROR_INTERRUPT
Sample Code
#define INCL_DOSMEMMGR
#include <os2.h>
#include <bsememf.h> /* This will get the memory managment flags */
PVOID BaseAddress; /* Pointer to the allocated memory block */
ULONG ObjectSize; /* The requested size of the memory block */
ULONG AllocationFlags; /* Flags */
APIRET rc; /* Will receive the return code */
ObjectSize = 9000; /* Asking for 9000 bytes, this will */
/* rounded up to 12KB. */
AllocationFlags = PAG_WRITE | PAG_EXECUTE;
/* Allows read/write to the memory block, but */
/* the block isn't committed within memory */
/* yet. */
rc = DosAllocMem(&BaseAddress, ObjectSize, AllocationFlags);
if ( rc != 0)
{
/* We have an error we must take care of. */
}