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>

1 files changed, 1 insertions, 0 deletions

diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
index 629a6dac33e1..3a79bde6bf5b 100644
--- a/arch/loongarch/Kconfig
+++ b/arch/loongarch/Kconfig
@@ -93,6 +93,7 @@ config LOONGARCH
 	select HAVE_DMA_CONTIGUOUS
 	select HAVE_DYNAMIC_FTRACE
 	select HAVE_DYNAMIC_FTRACE_WITH_ARGS
+	select HAVE_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
 	select HAVE_DYNAMIC_FTRACE_WITH_REGS
 	select HAVE_EBPF_JIT
 	select HAVE_EFFICIENT_UNALIGNED_ACCESS if !ARCH_STRICT_ALIGN