x86/boot: Put globals that are accessed early into the .data section

The helpers in arch/x86/boot/compressed/efi.c might be used during
early boot to access the EFI system/config tables, and in some cases
these EFI helpers might attempt to print debug/error messages, before
console_init() has been called.

__putstr() checks some variables to avoid printing anything before
the console has been initialized, but this isn't enough since those
variables live in .bss, which may not have been cleared yet. This can
lead to a triple-fault occurring, primarily when booting in legacy/CSM
mode (where EFI helpers will attempt to print some debug messages).

Fix this by declaring these globals in .data section instead so there
is no dependency on .bss being cleared before accessing them.

Fixes: c01fce9cef849 ("x86/compressed: Add SEV-SNP feature detection/setup")
Reported-by: Borislav Petkov <bp@suse.de>
Suggested-by: Thomas Lendacky <Thomas.Lendacky@amd.com>
Signed-off-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20220420152613.145077-1-michael.roth@amd.com

x86, boot: Don't compile early_serial_console.c when !CONFIG_EARLY_PRINTK

All the code in early_serial_console.c gets compiled out if
!CONFIG_EARLY_PRINTK, but early_serial_console.o itself still gets
compiled in. Eliminate it from the compile entirely in that case.

This does not change the generated code at all, in either case.

Signed-off-by: Josh Triplett <josh@joshtriplett.org>

x86, boot: Exclude early_serial_console.c if can't use it.

Removes early_serial_console.c code if we don't have the config option that
enables it (EARLY_PRINTK). When disabling this code, make early_serial_base a
constant 0 to allow the compiler to optimize away the code that checks for
early_serial_base.

Signed-off-by: Joe Millenbach <jmillenbach@gmail.com>
Link: http://lkml.kernel.org/r/1342746282-28497-7-git-send-email-jmillenbach@gmail.com
Signed-off-by: Gokul Caushik <caushik1@gmail.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

x86, setup: enable early console output from the decompressor

This enables the decompressor output to be seen on the serial console.
Most of the code is shared with the regular boot code.

We could add printf to the decompressor if needed, but currently there
is no sufficiently compelling user.

-v2: define BOOT_BOOT_H to avoid include boot.h
-v3: early_serial_base need to be static in misc.c ?
-v4: create seperate string.c printf.c cmdline.c early_serial_console.c
after hpa's patch that allow global variables in compressed/misc stage
-v5: remove printf.c related

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>