LoongArch: Add ORC stack unwinder support

The kernel CONFIG_UNWINDER_ORC option enables the ORC unwinder, which is
similar in concept to a DWARF unwinder. The difference is that the format
of the ORC data is much simpler than DWARF, which in turn allows the ORC
unwinder to be much simpler and faster.

The ORC data consists of unwind tables which are generated by objtool.
After analyzing all the code paths of a .o file, it determines information
about the stack state at each instruction address in the file and outputs
that information to the .orc_unwind and .orc_unwind_ip sections.

The per-object ORC sections are combined at link time and are sorted and
post-processed at boot time. The unwinder uses the resulting data to
correlate instruction addresses with their stack states at run time.

Most of the logic are similar with x86, in order to get ra info before ra
is saved into stack, add ra_reg and ra_offset into orc_entry. At the same
time, modify some arch-specific code to silence the objtool warnings.

Co-developed-by: Jinyang He <hejinyang@loongson.cn>
Signed-off-by: Jinyang He <hejinyang@loongson.cn>
Co-developed-by: Youling Tang <tangyouling@loongson.cn>
Signed-off-by: Youling Tang <tangyouling@loongson.cn>
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

LoongArch: Use SYM_CODE_* to annotate exception handlers

As described in include/linux/linkage.h,

FUNC -- C-like functions (proper stack frame etc.)
CODE -- non-C code (e.g. irq handlers with different, special stack etc.)

SYM_FUNC_{START, END} -- use for global functions
SYM_CODE_{START, END} -- use for non-C (special) functions

So use SYM_CODE_* to annotate exception handlers.

Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

LoongArch: Relay BCE exceptions to userland as SIGSEGV with si_code=SEGV_BNDERR

SEGV_BNDERR was introduced initially for supporting the Intel MPX, but
fell into disuse after the MPX support was removed. The LoongArch
bounds-checking instructions behave very differently than MPX, but
overall the interface is still kind of suitable for conveying the
information to userland when bounds-checking assertions trigger, so we
wouldn't have to invent more UAPI. Specifically, when the BCE triggers,
a SEGV_BNDERR is sent to userland, with si_addr set to the out-of-bounds
address or value (in asrt{gt,le}'s case), and one of si_lower or
si_upper set to the configured bound depending on the faulting
instruction. The other bound is set to either 0 or ULONG_MAX to resemble
a range with both lower and upper bounds.

Note that it is possible to have si_addr == si_lower in case of a
failing asrtgt or {ld,st}gt, because those instructions test for strict
greater-than relationship. This should not pose a problem for userland,
though, because the faulting PC is available for the application to
associate back to the exact instruction for figuring out the
expectation.

Example exception context generated by a faulting `asrtgt.d t0, t1`
(assert t0 > t1 or BCE) with t0=100 and t1=200:

> pc 00005555558206a4 ra 00007ffff2d854fc tp 00007ffff2f2f180 sp 00007ffffbf9fb80
> a0 0000000000000002 a1 00007ffffbf9fce8 a2 00007ffffbf9fd00 a3 00007ffff2ed4558
> a4 0000000000000000 a5 00007ffff2f044c8 a6 00007ffffbf9fce0 a7 fffffffffffff000
> t0 0000000000000064 t1 00000000000000c8 t2 00007ffffbfa2d5e t3 00007ffff2f12aa0
> t4 00007ffff2ed6158 t5 00007ffff2ed6158 t6 000000000000002e t7 0000000003d8f538
> t8 0000000000000005 u0 0000000000000000 s9 0000000000000000 s0 00007ffffbf9fce8
> s1 0000000000000002 s2 0000000000000000 s3 00007ffff2f2c038 s4 0000555555820610
> s5 00007ffff2ed5000 s6 0000555555827e38 s7 00007ffffbf9fd00 s8 0000555555827e38
> ra: 00007ffff2d854fc
> ERA: 00005555558206a4
> CRMD: 000000b0 (PLV0 -IE -DA +PG DACF=CC DACM=CC -WE)
> PRMD: 00000007 (PPLV3 +PIE -PWE)
> EUEN: 00000000 (-FPE -SXE -ASXE -BTE)
> ECFG: 0007181c (LIE=2-4,11-12 VS=7)
> ESTAT: 000a0000 [BCE] (IS= ECode=10 EsubCode=0)
> PRID: 0014c010 (Loongson-64bit, Loongson-3A5000)

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

LoongArch: Add la_abs macro implementation

Use the "la_abs macro" instead of the "la.abs pseudo instruction" to
prepare for the subsequent PIE kernel. When PIE is not enabled, la_abs
is equivalent to la.abs.

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

LoongArch: Add generic ex-handler unwind in prologue unwinder

When exception is triggered, code flow go handle_\exception in some
cases. One of stackframe in this case as follows,

high -> +-------+
| REGS | <- a pt_regs
| |
| | <- ex trigger
| REGS | <- ex pt_regs <-+
| | |
| | |
low -> +-------+ ->unwind-+

When unwinder unwinds to handler_\exception it cannot go on prologue
analysis. Because it is an asynchronous code flow, we should get the
next frame PC from regs->csr_era rather than regs->regs[1]. At init time
we copy the handlers to eentry and also copy them to NUMA-affine memory
named pcpu_handlers if NUMA is enabled. Thus, unwinder cannot unwind
normally. To solve this, we try to give some hints in handler_\exception
and fixup unwinders in unwind_next_frame().

Reported-by: Qing Zhang <zhangqing@loongson.cn>
Signed-off-by: Jinyang He <hejinyang@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

LoongArch: Re-tab the assembly files

Reflow the *.S files for better stylistic consistency, namely hard tabs
after mnemonic position, and vertical alignment of the first operand
with hard tabs. Tab width is obviously 8. Some pre-existing intra-block
vertical alignments are preserved.

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

LoongArch: Use the "jr" 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 exception/interrupt handling

Add the exception and interrupt handling machanism for basic LoongArch
support.

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