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#include <stdint.h>
// ARM lets you choose between 32-bit abd 64-bit translation table
// descriptors (called short and long descriptors respectively).
// The format of the descriptor differs depending on what it describes
// (section, supersection, a page table, etc...) and table of which
// level of lookup it belongs to.
// Even in case of descriptor of a specified type (e.g. short-format
// section descriptor), a given field inside it may have different
// meanings depending on settings in coprocessor registers... (yeah, ARM
// looks a bit messy... all for backward compatibility, i guess)
typedef struct
{
uint32_t PXN : 1; // bit 0
uint32_t Bit_1 : 1; // bit 1
uint32_t B : 1; // bit 2
uint32_t C : 1; // bit 3
uint32_t XN : 1; // bit 4
uint32_t Domain_3_0 : 4; // bits 8:5
uint32_t Bit_9 : 1; // bit 9
uint32_t AP_1_0 : 2; // bit 11:10
uint32_t TEX_2_0 : 3; // bits 14:12
uint32_t AP_2 : 1; // bit 15
uint32_t S : 1; // bit 16
uint32_t nG : 1; // bit 17
uint32_t Bit_18 : 1; // bit 18
uint32_t NS : 1; // bit 19
uint32_t PA_31_20 : 12; // bits 31:20
#define PRIVILEGED_EXECUTE_NEVER_BIT PXN
#define DESCRIPTOR_TYPE_2 Bit_1
#define BUFFERABLE_BIT B
#define CACHEABLE_BIT C
#define EXECUTE_NEVER_BIT XN
#define DOMAIN_3_0 Domain_3_0
#define IMPLEMENTATION_DEFINED_BIT Bit_9
#define ACCESS_PERMISSIONS_1_0 AP_1_0
#define TYPE_EXTENSION_2_0 TEX_2_0
#define ACCESS_PERMISSIONS_2 AP_2
#define SHAREABLE_BIT S
#define NON_GLOBAL_BIT nG
#define SECTION_OR_SUPERSECTION_BIT Bit_18
#define NON_SECURE_BIT NS
#define SECTION_BASE_ADDRESS_31_20 PA_31_20
} short_section_descriptor_t;
// How AP[2:0] is used depends on settings in SCTLR.AFE
// Meaning of #define'd names below:
// RW - read-write
// RO - read-only
// PL1 - a given permission applies to privilege level PL1
// PL2 - a given permission applies to privilege level PL2
// ALL - a given permission applies to both privilege levels
// If only a permission for one privilege level is given in the name,
// it means the other one has no access.
// When SCTLR.AFE is 0 (access flag not used) and short-format
// descritor table is used, the following access permission control
// schema for AP[2:0] is used:
#define AP_2_0_MODEL_NO_ACCESS 0b000
#define AP_2_0_MODEL_RW_PL1 0b001
#define AP_2_0_MODEL_RW_PL1_RO_PL0 0b010
#define AP_2_0_MODEL_RW_ALL 0b011
#define AP_2_0_MODEL_RESERVED 0b100
#define AP_2_0_MODEL_RO_PL1 0b101
#define AP_2_0_MODEL_RO_ALL_DEPRECATED 0b110 // use 0b111 instead
#define AP_2_0_MODEL_RO_ALL 0b111 // reserved in VMSAv6
// TODO: the #define's of RO_ALL and reserved could be done
// conditionally depending on the VMSA version available (either give
// the programmer #including this the possibility to #define their
// VMSA version or assume the VMSA version respective to the ARM
// version we're compiling against)
// Values for bit18, that determines whether a descriptor describes
// section or supersection:
#define DESCRIBES_SECTION 0b0
#define DESCRIBES_SUPERSECTION 0b1
typedef union
{
uint32_t raw;
uint8_t descriptor_type;
short_section_descriptor_t section_fields;
// more to come here (e.g. short_supersection_descriptor_t)
} short_descriptor_t;
// possible values of descriptor_type field:
#define SHORT_DESCRIPTOR_INVALID 0b00
#define SHORT_DESCRIPTOR_PAGE_TABLE 0b01
#define SHORT_DESCRIPTOR_SECTION_OR_SUPERSECTION 0b10
#define SHORT_DESCRIPTOR_SECTION_OR_SUPERSECTION_PXN 0b11
// on an implementation that does not support the PXN attribute
// 0b11 should not be used
#define SHORT_DESCRIPTOR_RESERVED 0b11
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