LoongArch: Fix definition of ftrace_regs_set_instruction_pointer()

The current definition of ftrace_regs_set_instruction_pointer() is not
correct. Obviously, this function is used to set instruction pointer but
not return value, so it should call instruction_pointer_set() instead of
regs_set_return_value().

There is no side effect by now because it is only used for kernel live-
patching which is not supported, so fix it to avoid failure when testing
livepatch in the future.

Fixes: 6fbff14a6382 ("LoongArch: ftrace: Abstract DYNAMIC_FTRACE_WITH_ARGS accesses")
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

LoongArch: ftrace: Enable HAVE_FUNCTION_GRAPH_RETVAL

The previous patch ("function_graph: Support recording and printing
the return value of function") has laid the groundwork for the for
the funcgraph-retval, and this modification makes it available on
the LoongArch platform.

We introduce a new structure called fgraph_ret_regs for the LoongArch
platform to hold return registers and the frame pointer. We then fill
its content in the return_to_handler and pass its address to the
function ftrace_return_to_handler to record the return value.

Link: https://lkml.kernel.org/r/c5462255e435fab363895c2d7433bc0f5a140411.1680954589.git.pengdonglin@sangfor.com.cn

Reviewed-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Donglin Peng <pengdonglin@sangfor.com.cn>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

LoongArch: ftrace: Add direct call support

Select the HAVE_DYNAMIC_FTRACE_WITH_DIRECT_CALLS to provide the
register_ftrace_direct[_multi] interfaces allowing users to register
the customed trampoline (direct_caller) as the mcount for one or more
target functions. And modify_ftrace_direct[_multi] are also provided
for modifying direct_caller.

There are a few cases to distinguish:
- If a direct call ops is the only one tracing a function AND the direct
called trampoline is within the reach of a 'bl' instruction
-> the ftrace patchsite jumps to the trampoline
- Else
-> the ftrace patchsite jumps to the ftrace_regs_caller trampoline points
to ftrace_list_ops so it iterates over all registered ftrace ops,
including the direct call ops and calls its call_direct_funcs handler
which stores the direct called trampoline's address in the ftrace_regs
and the ftrace_regs_caller trampoline will return to that address
instead of returning to the traced function

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

LoongArch: ftrace: Abstract DYNAMIC_FTRACE_WITH_ARGS accesses

Add new ftrace_regs_{get,set}_*() helpers which can be used to manipulate
ftrace_regs. When CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS=y, these can always
be used on any ftrace_regs, and when CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS
=n these can be used when regs are available.

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

LoongArch: Use correct sp value to get graph addr in stack unwinders

The stack frame when function_graph enable like follows,

--------- <- function sp_on_entry
|
|
|
FAKE_RA <- sp_on_entry - sizeof(pt_regs) + PT_R1
|
--------- <- sp_on_entry - sizeof(pt_regs)

So if we want to get the &FAKE_RA we should get sp_on_entry first. In
the unwinder_prologue case, we can get the sp_on_entry as state->sp,
because we try to calculate each CFA and the ra saved address. But in
the unwinder_guess case, we cannot get it because we do not try to
calculate the CFA. Although LoongArch have not fixed frame, the $ra is
saved at CFA - 8 in most cases, we can try guess, too. As we store the
pc in state, we not need to dereference state->sp, too.

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

LoongArch: modules/ftrace: Initialize PLT at load time

This patch implements ftrace trampolines through plt entry.

Tested by forcing ftrace_make_call() to use the module PLT, and then
loading up a module after setting up ftrace with:

| echo ":mod:<module-name>" > set_ftrace_filter;
| echo function > current_tracer;
| modprobe <module-name>

Since FTRACE_ADDR/FTRACE_REGS_ADDR is only defined when CONFIG_DYNAMIC_
FTRACE is selected, we wrap their usage in module_init_ftrace_plt() with
ifdeffery rather than using IS_ENABLED().

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

LoongArch/ftrace: Add HAVE_FUNCTION_GRAPH_RET_ADDR_PTR support

ftrace_graph_ret_addr() can be called by stack unwinding code to convert
a found stack return address ('ret') to its original value, in case the
function graph tracer has modified it to be 'return_to_handler'. If the
hasn't been modified, the unchanged value of 'ret' is returned.

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

LoongArch/ftrace: Add HAVE_DYNAMIC_FTRACE_WITH_ARGS support

Allow for arguments to be passed in to ftrace_regs by default. If this
is set, then arguments and stack can be found from the pt_regs.

1. HAVE_DYNAMIC_FTRACE_WITH_ARGS don't need special hook for graph
tracer entry point, but instead we can use graph_ops::func function to
install the return_hooker.

2. Livepatch requires this option in the future.

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

LoongArch/ftrace: Add HAVE_DYNAMIC_FTRACE_WITH_REGS support

This patch implements CONFIG_DYNAMIC_FTRACE_WITH_REGS on LoongArch,
which allows a traced function's arguments (and some other registers)
to be captured into a struct pt_regs, allowing these to be inspected
and modified.

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

LoongArch/ftrace: Add dynamic function tracer support

The compiler has inserted 2 NOPs before the regular function prologue.
T series registers are available and safe because of LoongArch's psABI.

At runtime, we can replace nop with bl to enable ftrace call and replace
bl with nop to disable ftrace call. The bl instruction requires us to
save the original RA value, so it saves RA at t0 here.

Details are:

| Compiled | Disabled | Enabled |
+------------+------------------------+------------------------+
| nop | move t0, ra | move t0, ra |
| nop | nop | bl ftrace_caller |
| func_body | func_body | func_body |

The RA value will be recovered by ftrace_regs_entry, and restored into
RA before returning to the regular function prologue. When a function is
not being traced, the "move t0, ra" is not harmful.

1) ftrace_make_call, ftrace_make_nop (in kernel/ftrace.c)
The two functions turn each recorded call site of filtered functions
into a call to ftrace_caller or nops.

2) ftracce_update_ftrace_func (in kernel/ftrace.c)
turns the nops at ftrace_call into a call to a generic entry for
function tracers.

3) ftrace_caller (in kernel/mcount_dyn.S)
The entry where each _mcount call sites calls to once they are
filtered to be traced.

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

LoongArch/ftrace: Add basic support

This patch contains basic ftrace support for LoongArch. Specifically,
function tracer (HAVE_FUNCTION_TRACER), function graph tracer (HAVE_
FUNCTION_GRAPH_TRACER) are implemented following the instructions in
Documentation/trace/ftrace-design.txt.

Use `-pg` makes stub like a child function `void _mcount(void *ra)`.
Thus, it can be seen store RA and alloc stack before `call _mcount`.
Find `alloc stack` at first, and then find `store RA`.

Note that the functions in both inst.c and time.c should not be hooked
with the compiler's -pg option: to prevent infinite self-referencing for
the former, and to ignore early setup stuff for the latter.

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