[v7,28/36] tracing: Add ftrace_partial_regs() for converting ftrace_regs to pt_regs

Commit Message

Masami Hiramatsu (Google) Feb. 6, 2024, 3:12 p.m. UTC

From: Masami Hiramatsu (Google) <[e-mail]>

Add ftrace_partial_regs() which converts the ftrace_regs to pt_regs.
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) <[e-mail]>
Acked-by: Florent Revest <[e-mail]>
---
 Changes from previous series: NOTHING, just forward ported.
---
 arch/arm64/include/asm/ftrace.h |   11 +++++++++++
 include/linux/ftrace.h          |   17 +++++++++++++++++
 2 files changed, 28 insertions(+)

Comments

Steven Rostedt Feb. 15, 2024, 4:11 p.m. UTC | #1

On Wed,  7 Feb 2024 00:12:40 +0900
"Masami Hiramatsu (Google)" <[e-mail]> wrote:

> From: Masami Hiramatsu (Google) <[e-mail]>
> 
> Add ftrace_partial_regs() which converts the ftrace_regs to pt_regs.
> 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.

This says what this patch is doing and not why it is doing it.

-- Steve

> 
> Signed-off-by: Masami Hiramatsu (Google) <[e-mail]>
> Acked-by: Florent Revest <[e-mail]>
> ---
>  Changes from previous series: NOTHING, just forward ported.
> ---

Masami Hiramatsu (Google) Feb. 16, 2024, 1:09 p.m. UTC | #2

On Thu, 15 Feb 2024 11:11:34 -0500
Steven Rostedt <[e-mail]> wrote:

> On Wed,  7 Feb 2024 00:12:40 +0900
> "Masami Hiramatsu (Google)" <[e-mail]> wrote:
> 
> > From: Masami Hiramatsu (Google) <[e-mail]>
> > 
> > Add ftrace_partial_regs() which converts the ftrace_regs to pt_regs.
> > 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.
> 
> This says what this patch is doing and not why it is doing it.

Hmm, OK. The reason is the eBPF 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 required.
I'll add this to next version.

Thanks,

> 
> -- Steve
> 
> > 
> > Signed-off-by: Masami Hiramatsu (Google) <[e-mail]>
> > Acked-by: Florent Revest <[e-mail]>
> > ---
> >  Changes from previous series: NOTHING, just forward ported.
> > ---

Steven Rostedt Feb. 16, 2024, 2:24 p.m. UTC | #3

On Fri, 16 Feb 2024 22:09:02 +0900
Masami Hiramatsu (Google) <[e-mail]> wrote:

> On Thu, 15 Feb 2024 11:11:34 -0500
> Steven Rostedt <[e-mail]> wrote:
> 
> > On Wed,  7 Feb 2024 00:12:40 +0900
> > "Masami Hiramatsu (Google)" <[e-mail]> wrote:
> >   
> > > From: Masami Hiramatsu (Google) <[e-mail]>
> > > 
> > > Add ftrace_partial_regs() which converts the ftrace_regs to pt_regs.
> > > 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.  
> > 
> > This says what this patch is doing and not why it is doing it.  
> 
> Hmm, OK. The reason is the eBPF 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 required.
> I'll add this to next version.

Thanks, that should go into the change log.

-- Steve

Patch

diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h
index efd5dbf74dd6..31051fa2b4d9 100644
--- a/arch/arm64/include/asm/ftrace.h
+++ b/arch/arm64/include/asm/ftrace.h
@@ -143,6 +143,17 @@  ftrace_override_function_with_return(struct ftrace_regs *fregs)
 	fregs->pc = fregs->lr;
 }
 
+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/include/linux/ftrace.h b/include/linux/ftrace.h
index a72a2eaec576..515ec804d605 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -173,6 +173,23 @@  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.