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authorRusty Russell <rusty@rustcorp.com.au>2008-03-28 11:05:53 -0500
committerRusty Russell <rusty@rustcorp.com.au>2008-03-28 11:05:54 +1100
commita6bd8e13034dd7d60b6f14217096efa192d0adc1 (patch)
tree23890908b06eb8357e6ce633d35df1216f5e4213 /arch/x86/lguest/i386_head.S
parente18b094f0faa4889b06a112da17230a10b88c815 (diff)
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lguest: comment documentation update.
Took some cycles to re-read the Lguest Journey end-to-end, fix some rot and tighten some phrases. Only comments change. No new jokes, but a couple of recycled old jokes. Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Diffstat (limited to 'arch/x86/lguest/i386_head.S')
-rw-r--r--arch/x86/lguest/i386_head.S15
1 files changed, 11 insertions, 4 deletions
diff --git a/arch/x86/lguest/i386_head.S b/arch/x86/lguest/i386_head.S
index 95b6fbc..5c7cef3 100644
--- 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
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