[PATCH v12 for-next 3/4] riscv: ftrace: Add DYNAMIC_FTRACE_WITH_DIRECT_CALLS support

Björn Töpel
2023-11-30T12:16:04Z

Select the 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.

To make the direct_caller and the other ftrace hooks (e.g.
function/fgraph tracer, k[ret]probes) co-exist, a temporary register
is nominated to store the address of direct_caller in
ftrace_regs_caller. After the setting of the address direct_caller by
direct_ops->func and the RESTORE_REGS in ftrace_regs_caller,
direct_caller will be jumped to by the `jr` inst.

Add DYNAMIC_FTRACE_WITH_DIRECT_CALLS support for RISC-V.

Signed-off-by: Song Shuai <suagrfillet@gmail.com>
Tested-by: Guo Ren <guoren@kernel.org>
Signed-off-by: Guo Ren <guoren@kernel.org>
Acked-by: Björn Töpel <bjorn@rivosinc.com>
---
arch/riscv/Kconfig | 1 +
arch/riscv/include/asm/ftrace.h | 7 +++++++
arch/riscv/kernel/mcount-dyn.S | 10 ++++++++++
3 files changed, 18 insertions(+)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 69c95e42be9f..4684cdc754a0 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -114,6 +114,7 @@ config RISCV
select HAVE_DEBUG_KMEMLEAK
select HAVE_DMA_CONTIGUOUS if MMU
select HAVE_DYNAMIC_FTRACE if !XIP_KERNEL && MMU && (CLANG_SUPPORTS_DYNAMIC_FTRACE || GCC_SUPPORTS_DYNAMIC_FTRACE)
+ select HAVE_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
select HAVE_DYNAMIC_FTRACE_WITH_REGS if HAVE_DYNAMIC_FTRACE
select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL
select HAVE_FUNCTION_GRAPH_TRACER
diff --git a/arch/riscv/include/asm/ftrace.h b/arch/riscv/include/asm/ftrace.h
index b383926f73be..329172122952 100644
--- a/arch/riscv/include/asm/ftrace.h
+++ b/arch/riscv/include/asm/ftrace.h
@@ -135,6 +135,13 @@ struct ftrace_regs;
void ftrace_graph_func(unsigned long ip, unsigned long parent_ip,
struct ftrace_ops *op, struct ftrace_regs *fregs);
#define ftrace_graph_func ftrace_graph_func
+
+static inline void __arch_ftrace_set_direct_caller(struct pt_regs *regs, unsigned long addr)
+{
+ regs->t1 = addr;
+}
+#define arch_ftrace_set_direct_caller(fregs, addr) \
+ __arch_ftrace_set_direct_caller(&(fregs)->regs, addr)
#endif /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */

#endif /* __ASSEMBLY__ */
diff --git a/arch/riscv/kernel/mcount-dyn.S b/arch/riscv/kernel/mcount-dyn.S
index c902a7ddb310..b7ce001779c1 100644
--- a/arch/riscv/kernel/mcount-dyn.S
+++ b/arch/riscv/kernel/mcount-dyn.S
@@ -229,6 +229,7 @@ SYM_FUNC_END(ftrace_caller)

#else /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
SYM_FUNC_START(ftrace_regs_caller)
+ mv t1, zero
SAVE_ABI_REGS 1
PREPARE_ARGS

@@ -236,7 +237,10 @@ SYM_INNER_LABEL(ftrace_regs_call, SYM_L_GLOBAL)
call ftrace_stub

RESTORE_ABI_REGS 1
+ bnez t1, .Ldirect
jr t0
+.Ldirect:
+ jr t1
SYM_FUNC_END(ftrace_regs_caller)

SYM_FUNC_START(ftrace_caller)
@@ -250,3 +254,9 @@ SYM_INNER_LABEL(ftrace_call, SYM_L_GLOBAL)
jr t0
SYM_FUNC_END(ftrace_caller)
#endif /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
+
+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
+SYM_CODE_START(ftrace_stub_direct_tramp)
+ jr t0
+SYM_CODE_END(ftrace_stub_direct_tramp)
+#endif /* CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS */