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Diffstat (limited to 'translation_table_descriptors.h')
| -rw-r--r-- | translation_table_descriptors.h | 99 |
1 files changed, 99 insertions, 0 deletions
diff --git a/translation_table_descriptors.h b/translation_table_descriptors.h new file mode 100644 index 0000000..35062f8 --- /dev/null +++ b/translation_table_descriptors.h @@ -0,0 +1,99 @@ +#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 + |