[PATCH v15 08/19] tracing: Add ftrace_partial_regs() for converting ftrace_regs to pt_regs

From: Masami Hiramatsu (Google)
Date: Sun Sep 15 2024 - 05:12:05 EST


From: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>

Add ftrace_partial_regs() which converts the ftrace_regs to pt_regs.
This is for the eBPF which needs this to keep the same pt_regs interface
to access registers.
Thus when replacing the pt_regs with ftrace_regs in fprobes (which is
used by kprobe_multi eBPF event), this will be used.

If the architecture defines its own ftrace_regs, this copies partial
registers to pt_regs and returns it. If not, ftrace_regs is the same as
pt_regs and ftrace_partial_regs() will return ftrace_regs::regs.

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
Acked-by: Florent Revest <revest@xxxxxxxxxxxx>
---
Changes in v14:
- Add riscv change.
Changes in v8:
- Add the reason why this required in changelog.
Changes from previous series: NOTHING, just forward ported.
---
arch/arm64/include/asm/ftrace.h | 11 +++++++++++
arch/riscv/include/asm/ftrace.h | 12 ++++++++++++
include/linux/ftrace.h | 17 +++++++++++++++++
3 files changed, 40 insertions(+)

diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h
index dffaab3dd1f1..5cd587afab6d 100644
--- a/arch/arm64/include/asm/ftrace.h
+++ b/arch/arm64/include/asm/ftrace.h
@@ -132,6 +132,17 @@ ftrace_regs_get_frame_pointer(const struct ftrace_regs *fregs)
return fregs->fp;
}

+static __always_inline struct pt_regs *
+ftrace_partial_regs(const struct ftrace_regs *fregs, struct pt_regs *regs)
+{
+ memcpy(regs->regs, fregs->regs, sizeof(u64) * 9);
+ regs->sp = fregs->sp;
+ regs->pc = fregs->pc;
+ regs->regs[29] = fregs->fp;
+ regs->regs[30] = fregs->lr;
+ return regs;
+}
+
int ftrace_regs_query_register_offset(const char *name);

int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec);
diff --git a/arch/riscv/include/asm/ftrace.h b/arch/riscv/include/asm/ftrace.h
index e9f364ce9fe8..897779dec402 100644
--- a/arch/riscv/include/asm/ftrace.h
+++ b/arch/riscv/include/asm/ftrace.h
@@ -193,6 +193,18 @@ static __always_inline void ftrace_override_function_with_return(struct ftrace_r
fregs->epc = fregs->ra;
}

+static __always_inline struct pt_regs *
+ftrace_partial_regs(const struct ftrace_regs *fregs, struct pt_regs *regs)
+{
+ memcpy(&regs->a0, fregs->args, sizeof(u64) * 8);
+ regs->epc = fregs->epc;
+ regs->ra = fregs->ra;
+ regs->sp = fregs->sp;
+ regs->s0 = fregs->s0;
+ regs->t1 = fregs->t1;
+ return regs;
+}
+
int ftrace_regs_query_register_offset(const char *name);

void ftrace_graph_func(unsigned long ip, unsigned long parent_ip,
diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index 35b5ed8867ca..d6b92a4091b9 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -176,6 +176,23 @@ static __always_inline struct pt_regs *ftrace_get_regs(struct ftrace_regs *fregs
return arch_ftrace_get_regs(fregs);
}

+#if !defined(CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS) || \
+ defined(CONFIG_HAVE_PT_REGS_TO_FTRACE_REGS_CAST)
+
+static __always_inline struct pt_regs *
+ftrace_partial_regs(struct ftrace_regs *fregs, struct pt_regs *regs)
+{
+ /*
+ * If CONFIG_HAVE_PT_REGS_TO_FTRACE_REGS_CAST=y, ftrace_regs memory
+ * layout is the same as pt_regs. So always returns that address.
+ * Since arch_ftrace_get_regs() will check some members and may return
+ * NULL, we can not use it.
+ */
+ return &fregs->regs;
+}
+
+#endif /* !CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS || CONFIG_HAVE_PT_REGS_TO_FTRACE_REGS_CAST */
+
/*
* When true, the ftrace_regs_{get,set}_*() functions may be used on fregs.
* Note: this can be true even when ftrace_get_regs() cannot provide a pt_regs.