Author: ian
Date: Wed Nov 28 18:09:42 2018
New Revision: 341160
URL: https://svnweb.freebsd.org/changeset/base/341160
Log:
Add comments describing the bootargs handoff between loader(8) and gptboot
or zfsboot, when loader(8) is the BTX loader. No functional changes.
Modified:
head/stand/i386/common/bootargs.h
head/stand/i386/gptboot/gptboot.c
head/stand/i386/zfsboot/zfsboot.c
Modified: head/stand/i386/common/bootargs.h
==============================================================================
--- head/stand/i386/common/bootargs.h Wed Nov 28 18:06:16 2018
(r341159)
+++ head/stand/i386/common/bootargs.h Wed Nov 28 18:09:42 2018
(r341160)
@@ -43,6 +43,24 @@
#ifndef __ASSEMBLER__
+/*
+ * This struct describes the contents of the stack on entry to btxldr.S. This
+ * is the data that follows the return address, so it begins at 4(%esp). On
+ * the sending side, this data is passed as individual args to __exec(). On
the
+ * receiving side, code in btxldr.S copies the data from the entry stack to a
+ * known fixed location in the new address space. Then, btxcsu.S sets the
+ * global variable __args to point to that known fixed location before calling
+ * main(), which casts __args to a struct bootargs pointer to access the data.
+ * The btxldr.S code is aware of KARGS_FLAGS_EXTARG, and if it's set, the extra
+ * args data is copied along with the other bootargs from the entry stack to
the
+ * fixed location in the new address space.
+ *
+ * The bootinfo field is actually a pointer to a bootinfo struct that has been
+ * converted to uint32_t using VTOP(). On the receiving side it must be
+ * converted back to a pointer using PTOV(). Code in btxldr.S is aware of this
+ * field and if it's non-NULL it copies the data it points to into another
known
+ * fixed location, and adjusts the bootinfo field to point to that new
location.
+ */
struct bootargs
{
uint32_t howto;
Modified: head/stand/i386/gptboot/gptboot.c
==============================================================================
--- head/stand/i386/gptboot/gptboot.c Wed Nov 28 18:06:16 2018
(r341159)
+++ head/stand/i386/gptboot/gptboot.c Wed Nov 28 18:09:42 2018
(r341160)
@@ -487,6 +487,12 @@ load(void)
geliargs.keybuf_sentinel = KEYBUF_SENTINEL;
geliargs.keybuf = gelibuf;
#endif
+ /*
+ * Note that the geliargs struct is passed by value, not by pointer.
+ * Code in btxldr.S copies the values from the entry stack to a fixed
+ * location within loader(8) at startup due to the presence of the
+ * KARGS_FLAGS_EXTARG flag.
+ */
__exec((caddr_t)addr, RB_BOOTINFO | (opts & RBX_MASK),
MAKEBOOTDEV(dev_maj[gdsk.dsk.type], gdsk.dsk.part + 1,
gdsk.dsk.unit, 0xff),
#ifdef LOADER_GELI_SUPPORT
Modified: head/stand/i386/zfsboot/zfsboot.c
==============================================================================
--- head/stand/i386/zfsboot/zfsboot.c Wed Nov 28 18:06:16 2018
(r341159)
+++ head/stand/i386/zfsboot/zfsboot.c Wed Nov 28 18:09:42 2018
(r341160)
@@ -1005,6 +1005,11 @@ load(void)
zfsargs.primary_vdev = primary_vdev->v_guid;
else
printf("failed to detect primary vdev\n");
+ /*
+ * Note that the zfsargs struct is passed by value, not by pointer. Code
in
+ * btxldr.S copies the values from the entry stack to a fixed location
+ * within loader(8) at startup due to the presence of KARGS_FLAGS_EXTARG.
+ */
__exec((caddr_t)addr, RB_BOOTINFO | (opts & RBX_MASK),
bootdev,
KARGS_FLAGS_ZFS | KARGS_FLAGS_EXTARG,
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