feat(x86_64): map the kernel in the higher half (#325)

Version [0.10.13][1] of `bootloader` made it possible to configure the
start address of the dynamic range into which the kernel binary is
mapped (see rust-osdev/bootloader#229). This allows us to configure the
bootloader to boot with the kernel already mapped into the higher half
of the virtual address space, which seems nice.

[1]: https://github.com/rust-osdev/bootloader/blob/main/Changelog.md#01013--2022-09-25

Cargo.toml

@@ -80,12 +80,15 @@ wat = "1.0"
 map-physical-memory = true
 map-page-table-recursively = true
 map-framebuffer = true
+# the kernel is mapped into the higher half of the virtual address space.
+dynamic-range-start = "0xFFFF_8000_0000_0000"
 
 [patch.crates-io]
 # use `tracing` 0.2 from git
 tracing = { git = "https://github.com/tokio-rs/tracing" }
 tracing-core = { git = "https://github.com/tokio-rs/tracing" }
 
+
 # Custom profile for Loom tests: enable release optimizations so that the loom
 # tests are less slow, but don't disable debug assertions.
 [profile.loom]

x86_64-mycelium.json

@@ -13,7 +13,9 @@
     "post-link-args": {
         "ld.lld": [
             "-z",
-            "nostart-stop-gc"
+            "nostart-stop-gc",
+            "--image-base",
+            "0xFFFF800000000000"
         ]
     },
     "panic-strategy": "abort",