Re: [PATCH bpf-next 1/5] arm64: ftrace: Add ftrace direct call support

On Apr 12, 2022, at 10:49 PM, Xu Kuohai xukuohai@huawei.com wrote:

Add ftrace direct support for arm64.

1. When there is custom trampoline only, replace the fentry nop to a

jump instruction that jumps directly to the custom trampoline.

2. When ftrace trampoline and custome coexist, jump from fentry to

ftrace trampoline first, then jump to custom trampoline when ftrace trampoline exits. The currently unused register pt_regs->x0 is used as an intermediary for jumping from ftrace trampoline to custom trampoline.

Signed-off-by: Xu Kuohai xukuohai@huawei.com

For the series:

Acked-by: Song Liu songliubraving@fb.com

(Pardon my laziness, I somehow only got 1/5 and 3/5 in one of my inboxes, and nothing in my other inbox. :( )

Just one nitpick for 2/5: as we move is_valid_bpf_tramp_flags to trampoline.c, we should change the multi-line comment into net style:

/* BPF_TRAMP_F_RET_FENTRY_RET is only used by bpf_struct_ops, * and it must be used alone. */

Thanks, Song

---

arch/arm64/Kconfig | 2 ++ arch/arm64/include/asm/ftrace.h | 10 ++++++++++ arch/arm64/kernel/asm-offsets.c | 1 + arch/arm64/kernel/entry-ftrace.S | 18 +++++++++++++++--- 4 files changed, 28 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index 57c4c995965f..81cc330daafc 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -177,6 +177,8 @@ config ARM64 select HAVE_DYNAMIC_FTRACE select HAVE_DYNAMIC_FTRACE_WITH_REGS \ if $(cc-option,-fpatchable-function-entry=2)

• select HAVE_DYNAMIC_FTRACE_WITH_DIRECT_CALLS \

• if DYNAMIC_FTRACE_WITH_REGS
  

  select FTRACE_MCOUNT_USE_PATCHABLE_FUNCTION_ENTRY \ if DYNAMIC_FTRACE_WITH_REGS select HAVE_EFFICIENT_UNALIGNED_ACCESS

diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h index 1494cfa8639b..3a363d6a3bd0 100644 --- a/arch/arm64/include/asm/ftrace.h +++ b/arch/arm64/include/asm/ftrace.h @@ -78,6 +78,16 @@ static inline unsigned long ftrace_call_adjust(unsigned long addr) return addr; }

+static inline void arch_ftrace_set_direct_caller(struct pt_regs *regs,

• 				 unsigned long addr)
  

+{

• /*

• * Place custom trampoline address in regs->orig_x0 to let ftrace
  

• * trampoline jump to it.
  

• */
  

• regs->orig_x0 = addr;

+}

#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS struct dyn_ftrace; int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec); diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c index 1197e7679882..b1ed0bf01c59 100644 --- a/arch/arm64/kernel/asm-offsets.c +++ b/arch/arm64/kernel/asm-offsets.c @@ -80,6 +80,7 @@ int main(void) DEFINE(S_SDEI_TTBR1, offsetof(struct pt_regs, sdei_ttbr1)); DEFINE(S_PMR_SAVE, offsetof(struct pt_regs, pmr_save)); DEFINE(S_STACKFRAME, offsetof(struct pt_regs, stackframe));

• DEFINE(S_ORIG_X0, offsetof(struct pt_regs, orig_x0)); DEFINE(PT_REGS_SIZE, sizeof(struct pt_regs)); BLANK();

#ifdef CONFIG_COMPAT diff --git a/arch/arm64/kernel/entry-ftrace.S b/arch/arm64/kernel/entry-ftrace.S index e535480a4069..b1bd6576f205 100644 --- a/arch/arm64/kernel/entry-ftrace.S +++ b/arch/arm64/kernel/entry-ftrace.S @@ -60,6 +60,9 @@ str x29, [sp, #S_FP] .endif

• /* Set orig_x0 to zero */
• str xzr, [sp, #S_ORIG_X0]
• /* Save the callsite's SP and LR */ add x10, sp, #(PT_REGS_SIZE + 16) stp x9, x10, [sp, #S_LR]

@@ -119,12 +122,21 @@ ftrace_common_return: /* Restore the callsite's FP, LR, PC */ ldr x29, [sp, #S_FP] ldr x30, [sp, #S_LR]

• ldr x9, [sp, #S_PC]

• ldr x10, [sp, #S_PC]
• ldr x11, [sp, #S_ORIG_X0]
• cbz x11, 1f
• /* Set x9 to parent ip before jump to bpf trampoline */
• mov x9, x30
• /* Set lr to self ip */
• ldr x30, [sp, #S_PC]
• /* Set x10 (used for return address) to bpf trampoline */
• mov x10, x11

+1: /* Restore the callsite's SP */ add sp, sp, #PT_REGS_SIZE + 16

• ret x9

• ret x10

SYM_CODE_END(ftrace_common)

#ifdef CONFIG_FUNCTION_GRAPH_TRACER

2.30.2