From: Masami Hiramatsu (Google) <mhiramat@kernel.org>

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@kernel.org>
Acked-by: Florent Revest <revest@chromium.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Albert Ou <aou@eecs.berkeley.edu>

---
 Changes in v18:
  - Fix to use sizeof() for calculating array size.
 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 |   13 +++++++++++++
 arch/riscv/include/asm/ftrace.h |   14 ++++++++++++++
 include/linux/ftrace.h          |   17 +++++++++++++++++
 3 files changed, 44 insertions(+)

diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h
index b5fa57b61378..09210f853f12 100644
--- a/arch/arm64/include/asm/ftrace.h
+++ b/arch/arm64/include/asm/ftrace.h
@@ -135,6 +135,19 @@ ftrace_regs_get_frame_pointer(const struct ftrace_regs *fregs)
 	return arch_ftrace_regs(fregs)->fp;
 }
 
+static __always_inline struct pt_regs *
+ftrace_partial_regs(const struct ftrace_regs *fregs, struct pt_regs *regs)
+{
+	struct __arch_ftrace_regs *afregs = arch_ftrace_regs(fregs);
+
+	memcpy(regs->regs, afregs->regs, sizeof(afregs->regs));
+	regs->sp = afregs->sp;
+	regs->pc = afregs->pc;
+	regs->regs[29] = afregs->fp;
+	regs->regs[30] = afregs->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 9372f8d7036f..7064a530794b 100644
--- a/arch/riscv/include/asm/ftrace.h
+++ b/arch/riscv/include/asm/ftrace.h
@@ -197,6 +197,20 @@ static __always_inline void ftrace_override_function_with_return(struct ftrace_r
 	arch_ftrace_regs(fregs)->epc = arch_ftrace_regs(fregs)->ra;
 }
 
+static __always_inline struct pt_regs *
+ftrace_partial_regs(const struct ftrace_regs *fregs, struct pt_regs *regs)
+{
+	struct __arch_ftrace_regs *afregs = arch_ftrace_regs(fregs);
+
+	memcpy(&regs->a0, afregs->args, sizeof(afregs->args));
+	regs->epc = afregs->epc;
+	regs->ra = afregs->ra;
+	regs->sp = afregs->sp;
+	regs->s0 = afregs->s0;
+	regs->t1 = afregs->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 bf8bb6c10553..ad2b46e1d5b0 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -190,6 +190,23 @@ 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_FTRACE_REGS_HAVING_PT_REGS)
+
+static __always_inline struct pt_regs *
+ftrace_partial_regs(struct ftrace_regs *fregs, struct pt_regs *regs)
+{
+	/*
+	 * If CONFIG_HAVE_FTRACE_REGS_HAVING_PT_REGS=y, ftrace_regs memory
+	 * layout is including 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 &arch_ftrace_regs(fregs)->regs;
+}
+
+#endif /* !CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS || CONFIG_HAVE_FTRACE_REGS_HAVING_PT_REGS */
+
 /*
  * 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.