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stivale2: Adjust the SMP part of the specification to mention that the BSP ID is not guaranteed to be 0

This commit is contained in:
mintsuki 2020-10-24 10:34:11 +02:00
parent e8f1c9437a
commit 01399b2e49
1 changed files with 12 additions and 3 deletions
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15
STIVALE2.md
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@ -389,7 +389,7 @@ struct stivale2_struct_tag_firmware {
#### SMP structure tag
This tag reports to the kernel info about the firmware.
This tag reports to the kernel info about a multiprocessor environment.
```c
struct stivale2_struct_tag_smp {
@ -405,6 +405,15 @@ struct stivale2_struct_tag_smp {
} __attribute__((packed));
```
*Note: In the code below, the BSP refers to the bootstrap processor,*
*AKA the processor that the system was started with, and the one whose*
*control is handed to by stivale2 first.*
*The LAPIC ID of the BSP is in most cases `0`, but this is not guaranteed.*
*To get the LAPIC ID of the BSP, see `CPUID` leaf `1`, and in case the*
*x2APIC is used, see `CPUID` leaves `0x1f` and `0xb`. Note that the `CPUID`*
*instruction has to be executed on the BSP itself.*
```c
struct stivale2_smp_info {
uint32_t acpi_processor_uid; // ACPI Processor UID as specified by MADT
@ -432,14 +441,14 @@ struct stivale2_smp_info {
// of ESP/RSP and RDI/stack arg being set up as
// above.
// goto_address is an unused field for the
// struct describing the BSP (lapic_id == 0)
// struct describing the BSP.
uint64_t extra_argument; // This field is here for the kernel to use
// for whatever it wants. Writes here should
// be performed before writing to goto_address
// so that the receiving processor can safely
// retrieve the data.
// extra_argument is an unused field for the
// struct describing the BSP (lapic_id == 0)
// struct describing the BSP.
} __attribute__((packed));
```