Ths page offset is defined in arch/XXX/constants.inc and needs to be
passed to the kernel so we can correctly calculate the physical frame
addresses that correspond to the ELF section virtual memory addresses.
The GDT is initially loaded in the 32-bit rt0 code where we cannot use
the 48-bit VMA for the GDT table and instead we use its physical
address. This approach works as the rt0 code establishes an identity
mapping for the region 0-8M. However, when the kernel creates a more
granular PDT it only includes the VMA addresses for the kernel ELF image
sections making the 0-8M invalid. Unless the GDT is reloaded with the
VMA of the table, the CPU will cause a non-recoverable page fault when
it tries to restore the segment registers while returning from a
recoverable page fault.
According to the ELF runtime handling of TLS document, the x86-64 arch
uses the same TLS handling variant (GNU) as the IA-32 ABI with the
exception that pointers are 8-byte wide and that the gs register is
swapped with fs. fs:0x0 points to the TCB; TLS variables are located
before it and are accessed using negative offsets from the TCB pointer.
In the Go case the G struct is accessed at fs:-0x8.
For more detauls see: https://www.akkadia.org/drepper/tls.pdf
By setting up pwd as a Go workspace, we can trim import paths from
something like "github.com/achilleasa/gopher-os/kernel" to just
"kernel".
These changes make forking easier and also allows us to move the code to
a different git hosting provider without having to rewrite the imports.
