ram64: Remove linux64_start

We now only support entrering the firmware though the PVH entry point

Signed-off-by: Joe Richey <joerichey@google.com>

Author: josephlr

layout.ld

@@ -1,4 +1,4 @@
-ENTRY(linux64_start)
+ENTRY(rust64_start) /* This firmware doesn't use the ELF entrypoint */
 
 PHDRS
 {

src/asm/mod.rs

@@ -1,2 +1 @@
 global_asm!(include_str!("ram32.s"));
-global_asm!(include_str!("ram64.s"));

src/asm/ram32.s

@@ -4,8 +4,6 @@
 ram32_start:
     # Stash the PVH start_info struct in %rdi.
     movl %ebx, %edi
-    # Zero out %rsi, its value is unspecificed in the PVH Boot Protocol.
-    xorl %esi, %esi
 
 setup_page_tables:
     # First L2 entry identity maps [0, 2 MiB)
@@ -42,5 +40,8 @@ jump_to_64bit:
     # We are now in 32-bit compatibility mode. To enter 64-bit mode, we need to
     # load a 64-bit code segment into our GDT.
     lgdtl GDT64_PTR
-    # Set CS to a 64-bit segment and jump to 64-bit code.
-    ljmpl $0x08, $ram64_start
+    # Initialize the stack pointer (Rust code always uses the stack)
+    movl $stack_start, %esp
+    # Set CS to a 64-bit segment and jump to 64-bit Rust code.
+    # PVH start_info is in %rdi, the first paramter of the System V ABI.
+    ljmpl $0x08, $rust64_start

src/asm/ram64.s

@@ -139,17 +139,13 @@ fn boot_from_device(device: &mut block::VirtioBlockDevice, info: &dyn boot::Info
 }
 
 #[no_mangle]
-pub extern "C" fn rust64_start(rdi: Option<&pvh::StartInfo>, rsi: Option<&boot::Params>) -> ! {
+pub extern "C" fn rust64_start(rdi: Option<&pvh::StartInfo>) -> ! {
     serial::PORT.borrow_mut().init();
 
     if let Some(start_info) = rdi {
         log!("\nBooting via PVH Boot Protocol");
         run(start_info)
     }
-    if let Some(boot_params) = rsi {
-        log!("\nBooting via Linux Boot Protocol");
-        run(boot_params)
-    }
     panic!("Unable to determine boot protocol")
 }