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authorPeter Jones <pjones@redhat.com>2013-03-06 13:00:23 -0500
committerH. Peter Anvin <hpa@zytor.com>2013-03-06 20:34:43 -0800
commit3c4aff6b9a183b4f24eb7b8dd6c8a92cdba3bc75 (patch)
tree1f5a62d998bf6c0e7ae66c9ecd2e95b7362c8875
parent2e604c0f19dcdd433b3863ffc3da9bc0787ca765 (diff)
downloadlinaro-lsk-3c4aff6b9a183b4f24eb7b8dd6c8a92cdba3bc75.tar.gz
x86, doc: Be explicit about what the x86 struct boot_params requires
If the sentinel triggers, we do not want the boot loader authors to just poke it and make the error go away, we want them to actually fix the problem. This should help avoid making the incorrect change in non-compliant bootloaders. [ hpa: dropped the Documentation/x86/boot.txt hunk pending clarifications ] Signed-off-by: Peter Jones <pjones@redhat.com> Link: http://lkml.kernel.org/r/1362592823-28967-1-git-send-email-pjones@redhat.com Signed-off-by: H. Peter Anvin <hpa@zytor.com>
-rw-r--r--arch/x86/include/asm/bootparam_utils.h16
1 files changed, 15 insertions, 1 deletions
diff --git a/arch/x86/include/asm/bootparam_utils.h b/arch/x86/include/asm/bootparam_utils.h
index ff808ef4fdb..653668d140f 100644
--- a/arch/x86/include/asm/bootparam_utils.h
+++ b/arch/x86/include/asm/bootparam_utils.h
@@ -19,8 +19,22 @@
*/
static void sanitize_boot_params(struct boot_params *boot_params)
{
+ /*
+ * IMPORTANT NOTE TO BOOTLOADER AUTHORS: do not simply clear
+ * this field. The purpose of this field is to guarantee
+ * compliance with the x86 boot spec located in
+ * Documentation/x86/boot.txt . That spec says that the
+ * *whole* structure should be cleared, after which only the
+ * portion defined by struct setup_header (boot_params->hdr)
+ * should be copied in.
+ *
+ * If you're having an issue because the sentinel is set, you
+ * need to change the whole structure to be cleared, not this
+ * (or any other) individual field, or you will soon have
+ * problems again.
+ */
if (boot_params->sentinel) {
- /*fields in boot_params are not valid, clear them */
+ /* fields in boot_params are left uninitialized, clear them */
memset(&boot_params->olpc_ofw_header, 0,
(char *)&boot_params->efi_info -
(char *)&boot_params->olpc_ofw_header);