pvh: Add PVH ELFNOTE

This adds information to the ELF binary so that a loader will know
where to start the executable. This now allows the firmware to be
booted via the PVH Boot Protocol.

Signed-off-by: Joe Richey <[email protected]>

layout.ld

@@ -3,6 +3,7 @@ ENTRY(linux64_start)
 PHDRS
 {
   ram  PT_LOAD FILEHDR PHDRS ;
+  note PT_NOTE               ;
 }
 
 /* Loaders like to put stuff in low memory (< 1M), so we don't use it. */
@@ -13,9 +14,10 @@ stack_size = 64K;
 
 SECTIONS
 {
-	/* Mapping the program headers into RAM makes the file smaller. */
+	/* Mapping the program headers and note into RAM makes the file smaller. */
 	. = ram_min;
 	. += SIZEOF_HEADERS;
+	.note : { *(.note) } :note :ram
 
 	/* These sections are mapped into RAM from the file. Omitting :ram from
 	   later sections avoids emitting empty sections in the final binary.     */

src/asm/mod.rs

@@ -1,3 +1,4 @@
+global_asm!(include_str!("note.s"));
 global_asm!(include_str!("ram32.s"));
 global_asm!(include_str!("ram64.s"));
 global_asm!(include_str!("gdt64.s"));

src/asm/note.s

@@ -0,0 +1,20 @@
+.section .note, "a"
+
+# From xen/include/public/elfnote.h, "Physical entry point into the kernel."
+XEN_ELFNOTE_PHYS32_ENTRY = 18
+
+# We don't bother defining an ELFNOTE macro, as we only have one note.
+# This is equialent to the kernel's:
+# ELFNOTE(Xen, XEN_ELFNOTE_PHYS32_ENTRY, .long pvh_start)
+.align 4
+    .long name_end - name_start    # namesz
+    .long desc_end - desc_start    # descsz
+    .long XEN_ELFNOTE_PHYS32_ENTRY # type
+name_start:
+    .asciz "Xen"
+name_end:
+.align 4
+desc_start:
+    .long ram32_start
+desc_end:
+.align 4