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 <joerichey@google.com>

Author: josephlr

layout.ld

@@ -3,6 +3,7 @@ ENTRY(linux64_start)
 PHDRS
 {
   program PT_LOAD FILEHDR PHDRS ;
+  note    PT_NOTE               ;
 }
 
 /* Loaders like to put stuff in low memory (< 1M), so we don't use it. */
@@ -26,6 +27,9 @@ SECTIONS
 
 	ASSERT((. <= ram_max - stack_size), "firmware size too big for RAM region")
 
+	/* These sections are not mapped into RAM */
+	.note   : { *(.note) } :note
+
 	/* Match edk2's GccBase.lds DISCARD section */
 	/DISCARD/ : {
 		*(.note.GNU-stack)

src/asm/mod.rs

@@ -1,2 +1,3 @@
+global_asm!(include_str!("note.s"));
 global_asm!(include_str!("ram32.s"));
 global_asm!(include_str!("ram64.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 pvh32_start
+desc_end:
+.align 4