Multiboot2 kernel support for i386

That implementation works either with BIOS or UEFI bootstrap

This requires the following kernel changes:

Add UEFI boot services and I/O method protoypes
src/sys/arch/x86/include/efi.h 1.8 - 1.9

Fix EFI system table mapping in virtual space
src/sys/arch/x86/x86/efi.c 1.19 - 1.20

Make sure no bioscall is issued when booting off UEFI system
src/sys/arch/i386/i386/machdep.c 1.821 - 1.822
src/sys/arch/i386/pci/piixpcib.c 1.22 - 1.23

And the following bootstrap changes:

Add kernel symbols for multiboot1
src/sys/arch/i386/stand/lib/exec_multiboot1.c 1.2 - 1.3
src/sys/arch/i386/stand/lib/libi386.h 1.45 - 1.47

Fix kernel symbols for multiboot2
src/sys/arch/i386/stand/lib/exec_multiboot2.c 1.2 - 1.3

Fix multiboot1 kernel symbol load

ELF_Shdr's sh_type field is a value, not a flag field

"s/ is is / is /" in comment. No functional change.

branches: 1.23.16; 1.23.18;
PR 51187 David Binderman: simplify redundant conditional

branches: 1.22.14;
Fix off by one.

branches: 1.21.8; 1.21.14; 1.21.18; 1.21.20;
As said in the comment (lines 327-336), we must make sure that
we don't overwrite valid data when moving the symbol and string
tables.

Assume for instance that the boot-loader left us with:

+--------------+ +--------+ +--------------+
| string table | | kernel | | symbol table |
+--------------+ +--------+ +--------------+

The new addresses computed by lines 338-359 (here, it's really
lines 344-345) will move the tables so that they end up as:

+--------+--------------+--------------+
| kernel | symbol table | string table |
+--------+--------------+--------------+

The current version (rev. 1.20) will, however, first copy the
string table and then the symbol table. But the copy of the
string table will overwrite the symbol table (see the pictures).

The old code (rev. 1.19) uses the right order of table copy to
make sure that we don't overwrite one table when moving the
other. Here, we simply restore this behavior. This makes
multibooting from GRUB2 work again (for MONOLITHIC).

ok jmcneill@

Welcome PAE inside i386 current.

This patch is inspired by work previously done by Jeremy Morse, ported by me
to -current, merged with the work previously done for port-xen, together with
additionals fixes and improvements.

PAE option is disabled by default in GENERIC (but will be enabled in ALL in
the next few days).

In quick, PAE switches the CPU to a mode where physical addresses become
36 bits (64 GiB). Virtual address space remains at 32 bits (4 GiB). To cope
with the increased size of the physical address, they are manipulated as
64 bits variables by kernel and MMU.

When supported by the CPU, it also allows the use of the NX/XD bit that
provides no-execution right enforcement on a per physical page basis.

Notes:

- reworked locore.S

- introduce cpu_load_pmap(), used to switch pmap for the curcpu. Due to the
different handling of pmap mappings with PAE vs !PAE, Xen vs native, details
are hidden within this function. This helps calling it from assembly,
as some features, like BIOS calls, switch to pmap_kernel before mapping
trampoline code in low memory.

- some changes in bioscall and kvm86_call, to reflect the above.

- the L3 is "pinned" per-CPU, and is only manipulated by a
reduced set of functions within pmap. To track the L3, I added two
elements to struct cpu_info, namely ci_l3_pdirpa (PA of the L3), and
ci_l3_pdir (the L3 VA). Rest of the code considers that it runs "just
like" a normal i386, except that the L2 is 4 pages long (PTP_LEVELS is
still 2).

- similar to the ci_pae_l3_pdir{,pa} variables, amd64's xen_current_user_pgd
becomes an element of cpu_info (slowly paving the way for MP world).

- bootinfo_source struct declaration is modified, to cope with paddr_t size
change with PAE (it is not correct to assume that bs_addr is a paddr_t when
compiled with PAE - it should remain 32 bits). bs_addrs is now a
void * array (in bootloader's code under i386/stand/, the bs_addrs
is a physaddr_t, which is an unsigned long).

- fixes in multiboot code (same reason as bootinfo): paddr_t size
change. I used Elf32_* types, use RELOC() where necessary, and move the
memcpy() functions out of the if/else if (I do not expect sym and str tables
to overlap with ELF).

- 64 bits atomic functions for pmap

- all pmap_pdirpa access are now done through the pmap_pdirpa macro. It
hides the L3/L2 stuff from PAE, as well as the pm_pdirpa change in
struct pmap (it now becomes a PDP_SIZE array, with or without PAE).

- manipulation of recursive mappings ( PDIR_SLOT_{,A}PTEs ) is done via
loops on PDP_SIZE.

See also http://mail-index.netbsd.org/port-i386/2010/07/17/msg002062.html

No objection raised on port-i386@ and port-xen@R for about a week.

XXX kvm(3) will be fixed in another patch to properly handle both PAE and !PAE
kernel dumps (VA => PA macros are slightly different, and need proper 64 bits
PA support in kvm_i386).

XXX Mixing PAE and !PAE modules may lead to unwanted/unexpected results. This
cannot be solved easily, and needs lots of thinking before being declared
safe (paddr_t/bus_addr_t size handling, PD/PT macros abstractions).

branches: 1.19.2; 1.19.4;
Add a missing opt_multiboot.h into sys/arch/i386/i386/machdep.c.
Also do the missed rename of multiboot_ksyms_init to
multiboot_ksyms_addsyms_elf to compile with MULTIBOOT set.

This caused a minor and a more serious bug in the past:
- dmesg did not contain the information about the loader
- /dev/ksyms did not work when the kernel was booted with a
multiboot bootloader (grub for example)

Ok by jmcneill, joerg.

branches: 1.18.4;
As discussed on tech-kern: mutex_init is too heavyweight for early bootstrap
phases, so move the initialization of the ksyms mutex back into main via
a function called ksyms_init. Rename the existing (but quite different)
ksyms_init* variations into ksyms_addsyms_elf() and ksyms_addsyms_explicit()
and adapt machdep code accordingly.

branches: 1.17.2;
Add "multiboot" command to boot multiboot compliant kernels like Xen.
Patch provided by Robert Swindell with fixes for the command line
parsing and addition of passing module options from me. The kernel now
always gets the full string for modules like for the command line,
everything before the first space/tab is the path name of the module.

branches: 1.16.6;
Remove clause 3 and 4 from TNF licenses

branches: 1.15.2; 1.15.4;
Fix esym calculation to match comments. Reported by Gao Ya'nan in
PR port-i386/38170.

Discard invalid console parameters, which cause initialization failures
later on. Reported by njoly@.

Drop trailing whitespace.

branches: 1.12.20; 1.12.36; 1.12.40;
TRUE -> true, FALSE -> false

Kill caddr_t; there will be some MI fallout, but it will be fixed shortly.

Replace the Mach-derived boolean_t type with the C99 bool type. A
future commit will replace use of TRUE and FALSE with true and false.

branches: 1.9.4;
Pass a simple ELF header to ksyms_init_explicit with the minimum contents
required to initialize ksyms_hdr. Otherwise LKMs do not work when using
ksyms_init_explicit instead of ksyms_init, as is the case of booting an
i386 kernel using Multiboot.

Remove the usage of Multiboot's "a.out kludge" to tell the boot loader to
reserve some more space for the BSS section than the binary says. This
trick was used to leave room after the kernel's image to copy the symbol
table following the format required by ksyms_init. (It was also used to
workaround a bug in the physical address fields of the binary, but this has
been long fixed.) Yes, the MULTIBOOT_SYMTAB_SPACE option goes away; yay!

Instead, copy the required data after the kernel in a way that avoids having
to reserve space and use the new ksyms_init_explicit function to avoid the
need to construct a minimal ELF image.

Fixes ksyms when using an "unpatched" GRUB (one that does not contain the
fix to honour the "a.out kludge" for ELF images, even when present) -- i.e.
ddb and lkms. As a side effect, the new code is much clearer to read and
digest.

Closes PR port-i386/32865.

- sprinkle __unused on function decls.
- fix a couple of unused bugs
- no more -Wno-unused for i386

branches: 1.6.4; 1.6.6; 1.6.8;
add a new "biosmem_implicit" variable that is set when a bootloader
info parser sets "biosbasemem" and "biosextmem" from. check for this
when probing memory size, rather than biosbasemem/biosextmem being
zero which is no longer true. also, make the REALBASEMEM/REALEXTMEM
options work properly with multiboot-booted kernels. fixes PR#33918.

PR/34007: Noriyuki Shiota: vmstat fails on the multiboot kernel booted by
GRUB-0.97. Initialize some previously unititiazed ELF header fields.

branches: 1.4.2; 1.4.4; 1.4.14;
Now that my idea to fix the detection of the boot device cannot work, reword
the 'XXX' comment and remove the marker. Also, in case there is no match,
fall back to wd0 instead of nothing.

Revert yesterday's change that attempted to fix the detection of the
boot device when using a Multiboot boot loader. It couldn't work because
these boot loaders do not pass a checksum of the disk so matchbiosdisk()
cannot really find any matches. I should have gone to sleep before
commiting...

Found by xtraeme@.

branches: 1.2.2;
When booting an i386 kernel with Multiboot, properly detect the boot device
by looking it up in the x86_alldisks table (instead of trying to match it
to 'wd*' manually).

In order to do this, move the cpu_rootconf function from x86 common code
to amd64 and i386 specific one. This way, i386 can do an extra step (call
the appropriate Multiboot code) in the appropriate place (after
x86_matchbiosdisks and before findroot()).

Implement support for 'The Multiboot Specification' so that i386 kernels
can be booted directly from Multiboot-compliant boot loaders (e.g. GRUB).
See the added multiboot(8) manual page for more information.

No objections in tech-kern@; only positive comments.

"s/ is is / is /" in comment. No functional change.

branches: 1.23.16;
PR 51187 David Binderman: simplify redundant conditional

branches: 1.22.14;
Fix off by one.

branches: 1.21.8; 1.21.14; 1.21.18; 1.21.20;
As said in the comment (lines 327-336), we must make sure that
we don't overwrite valid data when moving the symbol and string
tables.

Assume for instance that the boot-loader left us with:

+--------------+ +--------+ +--------------+
| string table | | kernel | | symbol table |
+--------------+ +--------+ +--------------+

The new addresses computed by lines 338-359 (here, it's really
lines 344-345) will move the tables so that they end up as:

+--------+--------------+--------------+
| kernel | symbol table | string table |
+--------+--------------+--------------+

The current version (rev. 1.20) will, however, first copy the
string table and then the symbol table. But the copy of the
string table will overwrite the symbol table (see the pictures).

The old code (rev. 1.19) uses the right order of table copy to
make sure that we don't overwrite one table when moving the
other. Here, we simply restore this behavior. This makes
multibooting from GRUB2 work again (for MONOLITHIC).

ok jmcneill@

Welcome PAE inside i386 current.

This patch is inspired by work previously done by Jeremy Morse, ported by me
to -current, merged with the work previously done for port-xen, together with
additionals fixes and improvements.

PAE option is disabled by default in GENERIC (but will be enabled in ALL in
the next few days).

In quick, PAE switches the CPU to a mode where physical addresses become
36 bits (64 GiB). Virtual address space remains at 32 bits (4 GiB). To cope
with the increased size of the physical address, they are manipulated as
64 bits variables by kernel and MMU.

When supported by the CPU, it also allows the use of the NX/XD bit that
provides no-execution right enforcement on a per physical page basis.

Notes:

- reworked locore.S

- introduce cpu_load_pmap(), used to switch pmap for the curcpu. Due to the
different handling of pmap mappings with PAE vs !PAE, Xen vs native, details
are hidden within this function. This helps calling it from assembly,
as some features, like BIOS calls, switch to pmap_kernel before mapping
trampoline code in low memory.

- some changes in bioscall and kvm86_call, to reflect the above.

- the L3 is "pinned" per-CPU, and is only manipulated by a
reduced set of functions within pmap. To track the L3, I added two
elements to struct cpu_info, namely ci_l3_pdirpa (PA of the L3), and
ci_l3_pdir (the L3 VA). Rest of the code considers that it runs "just
like" a normal i386, except that the L2 is 4 pages long (PTP_LEVELS is
still 2).

- similar to the ci_pae_l3_pdir{,pa} variables, amd64's xen_current_user_pgd
becomes an element of cpu_info (slowly paving the way for MP world).

- bootinfo_source struct declaration is modified, to cope with paddr_t size
change with PAE (it is not correct to assume that bs_addr is a paddr_t when
compiled with PAE - it should remain 32 bits). bs_addrs is now a
void * array (in bootloader's code under i386/stand/, the bs_addrs
is a physaddr_t, which is an unsigned long).

- fixes in multiboot code (same reason as bootinfo): paddr_t size
change. I used Elf32_* types, use RELOC() where necessary, and move the
memcpy() functions out of the if/else if (I do not expect sym and str tables
to overlap with ELF).

- 64 bits atomic functions for pmap

- all pmap_pdirpa access are now done through the pmap_pdirpa macro. It
hides the L3/L2 stuff from PAE, as well as the pm_pdirpa change in
struct pmap (it now becomes a PDP_SIZE array, with or without PAE).

- manipulation of recursive mappings ( PDIR_SLOT_{,A}PTEs ) is done via
loops on PDP_SIZE.

See also http://mail-index.netbsd.org/port-i386/2010/07/17/msg002062.html

No objection raised on port-i386@ and port-xen@R for about a week.

XXX kvm(3) will be fixed in another patch to properly handle both PAE and !PAE
kernel dumps (VA => PA macros are slightly different, and need proper 64 bits
PA support in kvm_i386).

XXX Mixing PAE and !PAE modules may lead to unwanted/unexpected results. This
cannot be solved easily, and needs lots of thinking before being declared
safe (paddr_t/bus_addr_t size handling, PD/PT macros abstractions).

branches: 1.19.2; 1.19.4;
Add a missing opt_multiboot.h into sys/arch/i386/i386/machdep.c.
Also do the missed rename of multiboot_ksyms_init to
multiboot_ksyms_addsyms_elf to compile with MULTIBOOT set.

This caused a minor and a more serious bug in the past:
- dmesg did not contain the information about the loader
- /dev/ksyms did not work when the kernel was booted with a
multiboot bootloader (grub for example)

Ok by jmcneill, joerg.

branches: 1.18.4;
As discussed on tech-kern: mutex_init is too heavyweight for early bootstrap
phases, so move the initialization of the ksyms mutex back into main via
a function called ksyms_init. Rename the existing (but quite different)
ksyms_init* variations into ksyms_addsyms_elf() and ksyms_addsyms_explicit()
and adapt machdep code accordingly.

branches: 1.17.2;
Add "multiboot" command to boot multiboot compliant kernels like Xen.
Patch provided by Robert Swindell with fixes for the command line
parsing and addition of passing module options from me. The kernel now
always gets the full string for modules like for the command line,
everything before the first space/tab is the path name of the module.

branches: 1.16.6;
Remove clause 3 and 4 from TNF licenses

branches: 1.15.2; 1.15.4;
Fix esym calculation to match comments. Reported by Gao Ya'nan in
PR port-i386/38170.

Discard invalid console parameters, which cause initialization failures
later on. Reported by njoly@.

Drop trailing whitespace.

branches: 1.12.20; 1.12.36; 1.12.40;
TRUE -> true, FALSE -> false

Kill caddr_t; there will be some MI fallout, but it will be fixed shortly.

Replace the Mach-derived boolean_t type with the C99 bool type. A
future commit will replace use of TRUE and FALSE with true and false.

branches: 1.9.4;
Pass a simple ELF header to ksyms_init_explicit with the minimum contents
required to initialize ksyms_hdr. Otherwise LKMs do not work when using
ksyms_init_explicit instead of ksyms_init, as is the case of booting an
i386 kernel using Multiboot.

Remove the usage of Multiboot's "a.out kludge" to tell the boot loader to
reserve some more space for the BSS section than the binary says. This
trick was used to leave room after the kernel's image to copy the symbol
table following the format required by ksyms_init. (It was also used to
workaround a bug in the physical address fields of the binary, but this has
been long fixed.) Yes, the MULTIBOOT_SYMTAB_SPACE option goes away; yay!

Instead, copy the required data after the kernel in a way that avoids having
to reserve space and use the new ksyms_init_explicit function to avoid the
need to construct a minimal ELF image.

Fixes ksyms when using an "unpatched" GRUB (one that does not contain the
fix to honour the "a.out kludge" for ELF images, even when present) -- i.e.
ddb and lkms. As a side effect, the new code is much clearer to read and
digest.

Closes PR port-i386/32865.

- sprinkle __unused on function decls.
- fix a couple of unused bugs
- no more -Wno-unused for i386

branches: 1.6.4; 1.6.6; 1.6.8;
add a new "biosmem_implicit" variable that is set when a bootloader
info parser sets "biosbasemem" and "biosextmem" from. check for this
when probing memory size, rather than biosbasemem/biosextmem being
zero which is no longer true. also, make the REALBASEMEM/REALEXTMEM
options work properly with multiboot-booted kernels. fixes PR#33918.

PR/34007: Noriyuki Shiota: vmstat fails on the multiboot kernel booted by
GRUB-0.97. Initialize some previously unititiazed ELF header fields.

branches: 1.4.2; 1.4.4; 1.4.14;
Now that my idea to fix the detection of the boot device cannot work, reword
the 'XXX' comment and remove the marker. Also, in case there is no match,
fall back to wd0 instead of nothing.

Revert yesterday's change that attempted to fix the detection of the
boot device when using a Multiboot boot loader. It couldn't work because
these boot loaders do not pass a checksum of the disk so matchbiosdisk()
cannot really find any matches. I should have gone to sleep before
commiting...

Found by xtraeme@.

branches: 1.2.2;
When booting an i386 kernel with Multiboot, properly detect the boot device
by looking it up in the x86_alldisks table (instead of trying to match it
to 'wd*' manually).

In order to do this, move the cpu_rootconf function from x86 common code
to amd64 and i386 specific one. This way, i386 can do an extra step (call
the appropriate Multiboot code) in the appropriate place (after
x86_matchbiosdisks and before findroot()).

Implement support for 'The Multiboot Specification' so that i386 kernels
can be booted directly from Multiboot-compliant boot loaders (e.g. GRUB).
See the added multiboot(8) manual page for more information.

No objections in tech-kern@; only positive comments.

PR 51187 David Binderman: simplify redundant conditional

branches: 1.22.14;
Fix off by one.

branches: 1.21.8; 1.21.14; 1.21.18; 1.21.20;
As said in the comment (lines 327-336), we must make sure that
we don't overwrite valid data when moving the symbol and string
tables.

Assume for instance that the boot-loader left us with:

+--------------+ +--------+ +--------------+
| string table | | kernel | | symbol table |
+--------------+ +--------+ +--------------+

The new addresses computed by lines 338-359 (here, it's really
lines 344-345) will move the tables so that they end up as:

+--------+--------------+--------------+
| kernel | symbol table | string table |
+--------+--------------+--------------+

The current version (rev. 1.20) will, however, first copy the
string table and then the symbol table. But the copy of the
string table will overwrite the symbol table (see the pictures).

The old code (rev. 1.19) uses the right order of table copy to
make sure that we don't overwrite one table when moving the
other. Here, we simply restore this behavior. This makes
multibooting from GRUB2 work again (for MONOLITHIC).

ok jmcneill@

Welcome PAE inside i386 current.

This patch is inspired by work previously done by Jeremy Morse, ported by me
to -current, merged with the work previously done for port-xen, together with
additionals fixes and improvements.

PAE option is disabled by default in GENERIC (but will be enabled in ALL in
the next few days).

In quick, PAE switches the CPU to a mode where physical addresses become
36 bits (64 GiB). Virtual address space remains at 32 bits (4 GiB). To cope
with the increased size of the physical address, they are manipulated as
64 bits variables by kernel and MMU.

When supported by the CPU, it also allows the use of the NX/XD bit that
provides no-execution right enforcement on a per physical page basis.

Notes:

- reworked locore.S

- introduce cpu_load_pmap(), used to switch pmap for the curcpu. Due to the
different handling of pmap mappings with PAE vs !PAE, Xen vs native, details
are hidden within this function. This helps calling it from assembly,
as some features, like BIOS calls, switch to pmap_kernel before mapping
trampoline code in low memory.

- some changes in bioscall and kvm86_call, to reflect the above.

- the L3 is "pinned" per-CPU, and is only manipulated by a
reduced set of functions within pmap. To track the L3, I added two
elements to struct cpu_info, namely ci_l3_pdirpa (PA of the L3), and
ci_l3_pdir (the L3 VA). Rest of the code considers that it runs "just
like" a normal i386, except that the L2 is 4 pages long (PTP_LEVELS is
still 2).

- similar to the ci_pae_l3_pdir{,pa} variables, amd64's xen_current_user_pgd
becomes an element of cpu_info (slowly paving the way for MP world).

- bootinfo_source struct declaration is modified, to cope with paddr_t size
change with PAE (it is not correct to assume that bs_addr is a paddr_t when
compiled with PAE - it should remain 32 bits). bs_addrs is now a
void * array (in bootloader's code under i386/stand/, the bs_addrs
is a physaddr_t, which is an unsigned long).

- fixes in multiboot code (same reason as bootinfo): paddr_t size
change. I used Elf32_* types, use RELOC() where necessary, and move the
memcpy() functions out of the if/else if (I do not expect sym and str tables
to overlap with ELF).

- 64 bits atomic functions for pmap

- all pmap_pdirpa access are now done through the pmap_pdirpa macro. It
hides the L3/L2 stuff from PAE, as well as the pm_pdirpa change in
struct pmap (it now becomes a PDP_SIZE array, with or without PAE).

- manipulation of recursive mappings ( PDIR_SLOT_{,A}PTEs ) is done via
loops on PDP_SIZE.

See also http://mail-index.netbsd.org/port-i386/2010/07/17/msg002062.html

No objection raised on port-i386@ and port-xen@R for about a week.

XXX kvm(3) will be fixed in another patch to properly handle both PAE and !PAE
kernel dumps (VA => PA macros are slightly different, and need proper 64 bits
PA support in kvm_i386).

XXX Mixing PAE and !PAE modules may lead to unwanted/unexpected results. This
cannot be solved easily, and needs lots of thinking before being declared
safe (paddr_t/bus_addr_t size handling, PD/PT macros abstractions).

branches: 1.19.2; 1.19.4;
Add a missing opt_multiboot.h into sys/arch/i386/i386/machdep.c.
Also do the missed rename of multiboot_ksyms_init to
multiboot_ksyms_addsyms_elf to compile with MULTIBOOT set.

This caused a minor and a more serious bug in the past:
- dmesg did not contain the information about the loader
- /dev/ksyms did not work when the kernel was booted with a
multiboot bootloader (grub for example)

Ok by jmcneill, joerg.

branches: 1.18.4;
As discussed on tech-kern: mutex_init is too heavyweight for early bootstrap
phases, so move the initialization of the ksyms mutex back into main via
a function called ksyms_init. Rename the existing (but quite different)
ksyms_init* variations into ksyms_addsyms_elf() and ksyms_addsyms_explicit()
and adapt machdep code accordingly.

branches: 1.17.2;
Add "multiboot" command to boot multiboot compliant kernels like Xen.
Patch provided by Robert Swindell with fixes for the command line
parsing and addition of passing module options from me. The kernel now
always gets the full string for modules like for the command line,
everything before the first space/tab is the path name of the module.

branches: 1.16.6;
Remove clause 3 and 4 from TNF licenses

branches: 1.15.2; 1.15.4;
Fix esym calculation to match comments. Reported by Gao Ya'nan in
PR port-i386/38170.

Discard invalid console parameters, which cause initialization failures
later on. Reported by njoly@.

Drop trailing whitespace.

branches: 1.12.20; 1.12.36; 1.12.40;
TRUE -> true, FALSE -> false

Kill caddr_t; there will be some MI fallout, but it will be fixed shortly.

Replace the Mach-derived boolean_t type with the C99 bool type. A
future commit will replace use of TRUE and FALSE with true and false.

branches: 1.9.4;
Pass a simple ELF header to ksyms_init_explicit with the minimum contents
required to initialize ksyms_hdr. Otherwise LKMs do not work when using
ksyms_init_explicit instead of ksyms_init, as is the case of booting an
i386 kernel using Multiboot.

Remove the usage of Multiboot's "a.out kludge" to tell the boot loader to
reserve some more space for the BSS section than the binary says. This
trick was used to leave room after the kernel's image to copy the symbol
table following the format required by ksyms_init. (It was also used to
workaround a bug in the physical address fields of the binary, but this has
been long fixed.) Yes, the MULTIBOOT_SYMTAB_SPACE option goes away; yay!

Instead, copy the required data after the kernel in a way that avoids having
to reserve space and use the new ksyms_init_explicit function to avoid the
need to construct a minimal ELF image.

Fixes ksyms when using an "unpatched" GRUB (one that does not contain the
fix to honour the "a.out kludge" for ELF images, even when present) -- i.e.
ddb and lkms. As a side effect, the new code is much clearer to read and
digest.

Closes PR port-i386/32865.

- sprinkle __unused on function decls.
- fix a couple of unused bugs
- no more -Wno-unused for i386

branches: 1.6.4; 1.6.6; 1.6.8;
add a new "biosmem_implicit" variable that is set when a bootloader
info parser sets "biosbasemem" and "biosextmem" from. check for this
when probing memory size, rather than biosbasemem/biosextmem being
zero which is no longer true. also, make the REALBASEMEM/REALEXTMEM
options work properly with multiboot-booted kernels. fixes PR#33918.

PR/34007: Noriyuki Shiota: vmstat fails on the multiboot kernel booted by
GRUB-0.97. Initialize some previously unititiazed ELF header fields.

branches: 1.4.2; 1.4.4; 1.4.14;
Now that my idea to fix the detection of the boot device cannot work, reword
the 'XXX' comment and remove the marker. Also, in case there is no match,
fall back to wd0 instead of nothing.

Revert yesterday's change that attempted to fix the detection of the
boot device when using a Multiboot boot loader. It couldn't work because
these boot loaders do not pass a checksum of the disk so matchbiosdisk()
cannot really find any matches. I should have gone to sleep before
commiting...

Found by xtraeme@.

branches: 1.2.2;
When booting an i386 kernel with Multiboot, properly detect the boot device
by looking it up in the x86_alldisks table (instead of trying to match it
to 'wd*' manually).

In order to do this, move the cpu_rootconf function from x86 common code
to amd64 and i386 specific one. This way, i386 can do an extra step (call
the appropriate Multiboot code) in the appropriate place (after
x86_matchbiosdisks and before findroot()).

Implement support for 'The Multiboot Specification' so that i386 kernels
can be booted directly from Multiboot-compliant boot loaders (e.g. GRUB).
See the added multiboot(8) manual page for more information.

No objections in tech-kern@; only positive comments.