On Wed, 9 Aug 2023 12:31:27 +0200
Florent Revest [off-list ref] wrote:

On Mon, Aug 7, 2023 at 8:49 AM Masami Hiramatsu (Google)
[off-list ref] wrote:

quoted

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

Add ftrace_partial_regs() which converts the ftrace_regas to pt_regs.

ftrace_regs*

Oops, thanks.

quoted

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>
---
 arch/arm64/include/asm/ftrace.h |   11 +++++++++++
 include/linux/ftrace.h          |   11 +++++++++++
 2 files changed, 22 insertions(+)

diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h
index ab158196480c..b108cd6718cf 100644
--- a/arch/arm64/include/asm/ftrace.h
+++ b/arch/arm64/include/asm/ftrace.h

@@ -137,6 +137,17 @@ 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) * 10);

Are you intentionally copying that tenth value (fregs.direct_tramp)
into pt_regs.regs[9] ? This seems wrong and it looks like it will bite
us back one day. Isn't it one of these cases where we can simply use
sizeof(fregs->regs) ?

Ah, sorry, it was my mistake. It should be "sizeof(u64) * 9".
I would like to know how can I handle the 'direct_tramp' thing?
Can I just ignore it?

quoted

+       regs->sp = fregs->sp;
+       regs->pc = fregs->pc;
+       regs->x[29] = fregs->fp;
+       regs->x[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 3fb94a1a2461..7f45654441b7 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h

@@ -155,6 +155,17 @@ 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_COMPAT_FTRACE_REGS)
+
+static __always_inline struct pt_regs *
+ftrace_partial_regs(const struct ftrace_regs *fregs, struct pt_regs *regs)
+{
+       return arch_ftrace_get_regs((struct ftrace_regs *)fregs);
+}

I don't think this works. Suppose you are on x86, WITH_ARGS, and with
HAVE_PT_REGS_COMPAT_FTRACE_REGS. If you register to ftrace without
FTRACE_OPS_FL_SAVE_REGS you will receive a ftrace_regs from the light
ftrace pre-trampoline that has a CS register equal to 0 and
arch_ftrace_get_regs will return NULL here, which should never happen.

Yes, Jiri also pointed it. So I simply made it (also remove 'const' from fregs)

return &fregs->regs;

Thank you,

Have you tested your series without registering as FTRACE_OPS_FL_SAVE_REGS ?

-- 
Masami Hiramatsu (Google) [off-list ref]