[PATCH 1/2] riscv: ftrace: Add DYNAMIC_FTRACE_WITH_DIRECT_CALLS support

guoren
2022-11-28T10:12:39Z

From: Song Shuai <suagrfillet@gmail.com>

This patch adds DYNAMIC_FTRACE_WITH_DIRECT_CALLS support for RISC-V.

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 (eg. 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.

Signed-off-by: Song Shuai <suagrfillet@gmail.com>
Co-developed-by: Guo Ren <guoren@kernel.org>
Signed-off-by: Guo Ren <guoren@kernel.org>
---
Remove modification of mcount-dyn.S. (Guo Ren)
---
arch/riscv/Kconfig | 1 +
arch/riscv/include/asm/ftrace.h | 26 ++++++++++++++++++++++++++
2 files changed, 27 insertions(+)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 1d0e5838b11b..2828537abfcd 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -278,6 +278,7 @@ config ARCH_RV64I
select ARCH_SUPPORTS_INT128 if CC_HAS_INT128
select HAVE_DYNAMIC_FTRACE if !XIP_KERNEL && MMU && $(cc-option,-fpatchable-function-entry=8)
select HAVE_DYNAMIC_FTRACE_WITH_REGS if HAVE_DYNAMIC_FTRACE
+ select HAVE_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL
select HAVE_FUNCTION_GRAPH_TRACER
select HAVE_FUNCTION_TRACER if !XIP_KERNEL && !PREEMPTION
diff --git a/arch/riscv/include/asm/ftrace.h b/arch/riscv/include/asm/ftrace.h
index 84f856a3286e..d2c159cdfa5c 100644
--- a/arch/riscv/include/asm/ftrace.h
+++ b/arch/riscv/include/asm/ftrace.h
@@ -114,6 +114,32 @@ 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)
+{
+ /*
+ * Backup origin detour target (t0) in t1, and set t0 with addr.
+ *
+ * Here is the sample code for riscv direct_caller:
+ *
+ * addi sp,sp,-16
+ * move t0,t1
+ * ^^^^^^^^^^
+ * sd t0,0(sp)
+ * sd ra,8(sp)
+ * call my_direct_func1
+ * ld t0,0(sp)
+ * ld ra,8(sp)
+ * addi sp,sp,16
+ * jr t0
+ *
+ * (Set t0 with t1 for continuous detour, because t1 contains origin detour
+ * target)
+ */
+ regs->t1 = regs->t0;
+ regs->t0 = addr;
+}
+
#endif /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */

#endif /* __ASSEMBLY__ */
--
2.36.1