LoongArch: extable: Add a dedicated uaccess handler

Inspired by commit 2e77a62cb3a6("arm64: extable: add a dedicated uaccess
handler"), do similar to LoongArch to add a dedicated uaccess exception
handler to update registers in exception context and subsequently return
back into the function which faulted, so we remove the need for fixups
specialized to each faulting instruction.

Add gpr-num.h here because we need to map the same GPR names to integer
constants, so that we can use this to build meta-data for the exception
fixups.

The compiler treats gpr 0 as zero rather than $r0, so set it separately
to .L__gpr_num_zero, otherwise the following assembly error will occurs:

{standard input}: Assembler messages:
{standard input}:1074: Error: invalid operands (*UND* and *ABS* sections) for `<<'
{standard input}:1160: Error: invalid operands (*UND* and *ABS* sections) for `<<'
make[1]: *** [scripts/Makefile.build:249: fs/fcntl.o] Error 1

Signed-off-by: Youling Tang <tangyouling@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

LoongArch: Consolidate __ex_table construction

Consolidate all the __ex_table constuction code with a _ASM_EXTABLE or
_asm_extable helper.

There should be no functional change as a result of this patch.

Signed-off-by: Youling Tang <tangyouling@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

LoongArch: Remove useless header compiler.h

The content of LoongArch's compiler.h is trivial, with some unused
anywhere, so inline the definitions and remove the header.

Signed-off-by: Jun Yi <yijun@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

LoongArch: Simplify "BEQ/BNE foo, zero" with BEQZ/BNEZ

While B{EQ,NE}Z and B{EQ,NE} are different instructions, and the vastly
expanded range for branch destination does not really matter in the few
cases touched, use the B{EQ,NE}Z where possible for shorter lines and
better consistency (e.g. some places used "BEQ foo, zero", while some
used "BEQ zero, foo").

Signed-off-by: WANG Xuerui <git@xen0n.name>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

LoongArch: Use the "move" pseudo-instruction where applicable

Some of the assembly code in the LoongArch port likely originated
from a time when the assembler did not support pseudo-instructions like
"move" or "jr", so the desugared form was used and readability suffers
(to a minor degree) as a result.

As the upstream toolchain supports these pseudo-instructions from the
beginning, migrate the existing few usages to them for better
readability.

Signed-off-by: WANG Xuerui <git@xen0n.name>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

LoongArch: Add multi-processor (SMP) support

LoongArch-based procesors have 4, 8 or 16 cores per package. This patch
adds multi-processor (SMP) support for LoongArch.

Reviewed-by: WANG Xuerui <git@xen0n.name>
Reviewed-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

LoongArch: Add misc common routines

Add some misc common routines for LoongArch, including: asm-offsets
routines, futex functions, i/o memory access functions, frame-buffer
functions, procfs information display, etc.

Reviewed-by: WANG Xuerui <git@xen0n.name>
Reviewed-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>