lguest: comment documentation update.

[linux-2.6-omap-h63xx.git] / arch / x86 / lguest / i386_head.S

diff --git a/arch/x86/lguest/i386_head.S b/arch/x86/lguest/i386_head.S
index 95b6fbcded63232ffbb614f493741575d4413829..5c7cef34c9e70d31d96fc47e002fd6b6bcd8d590 100644 (file)
--- a/arch/x86/lguest/i386_head.S
+++ b/arch/x86/lguest/i386_head.S
@@ -5,13 +5,20 @@
 #include <asm/thread_info.h>
 #include <asm/processor-flags.h>
 
-/*G:020 This is where we begin: head.S notes that the boot header's platform
- * type field is "1" (lguest), so calls us here.
+/*G:020 Our story starts with the kernel booting into startup_32 in
+ * arch/x86/kernel/head_32.S.  It expects a boot header, which is created by
+ * the bootloader (the Launcher in our case).
+ *
+ * The startup_32 function does very little: it clears the uninitialized global
+ * C variables which we expect to be zero (ie. BSS) and then copies the boot
+ * header and kernel command line somewhere safe.  Finally it checks the
+ * 'hardware_subarch' field.  This was introduced in 2.6.24 for lguest and Xen:
+ * if it's set to '1' (lguest's assigned number), then it calls us here.
  *
  * WARNING: be very careful here!  We're running at addresses equal to physical
  * addesses (around 0), not above PAGE_OFFSET as most code expectes
  * (eg. 0xC0000000).  Jumps are relative, so they're OK, but we can't touch any
- * data.
+ * data without remembering to subtract __PAGE_OFFSET!
  *
  * The .section line puts this code in .init.text so it will be discarded after
  * boot. */
@@ -24,7 +31,7 @@ ENTRY(lguest_entry)
        int $LGUEST_TRAP_ENTRY
 
        /* The Host put the toplevel pagetable in lguest_data.pgdir.  The movsl
-        * instruction uses %esi implicitly as the source for the copy we'
+        * instruction uses %esi implicitly as the source for the copy we're
         * about to do. */
        movl lguest_data - __PAGE_OFFSET + LGUEST_DATA_pgdir, %esi