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Add comments describing the bootargs handoff between loader(8) and gptboot

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or zfsboot, when loader(8) is the BTX loader.  No functional changes.
This commit is contained in:
ian 2018-11-28 18:09:42 +00:00
parent 0a3c73d350
commit 80670fa92d
3 changed files with 29 additions and 0 deletions
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18
stand/i386/common/bootargs.h
View File

@ -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;

6
stand/i386/gptboot/gptboot.c
View File

@ -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

5
stand/i386/zfsboot/zfsboot.c
View File

@ -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,