linux-kernel - [PATCH v6 3/5] samples: ftrace: Save required argument registers in sample trampolines

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Date:   Wed,  5 Apr 2023 20:02:48 +0200
From:   Florent Revest <revest@...omium.org>
To:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-trace-kernel@...r.kernel.org, bpf@...r.kernel.org
Cc:     catalin.marinas@....com, will@...nel.org, rostedt@...dmis.org,
        mhiramat@...nel.org, mark.rutland@....com, ast@...nel.org,
        daniel@...earbox.net, andrii@...nel.org, kpsingh@...nel.org,
        jolsa@...nel.org, xukuohai@...weicloud.com, lihuafei1@...wei.com,
        Florent Revest <revest@...omium.org>
Subject: [PATCH v6 3/5] samples: ftrace: Save required argument registers in sample trampolines

The ftrace-direct-too sample traces the handle_mm_fault function whose
signature changed since the introduction of the sample. Since:
commit bce617edecad ("mm: do page fault accounting in handle_mm_fault")
handle_mm_fault now has 4 arguments. Therefore, the sample trampoline
should save 4 argument registers.

s390 saves all argument registers already so it does not need a change
but x86_64 needs an extra push and pop.

This also evolves the signature of the tracing function to make it
mirror the signature of the traced function.

Signed-off-by: Florent Revest <revest@...omium.org>
---
 samples/ftrace/ftrace-direct-too.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/samples/ftrace/ftrace-direct-too.c b/samples/ftrace/ftrace-direct-too.c
index f28e7b99840f..71ed4ee8cb4a 100644
--- a/samples/ftrace/ftrace-direct-too.c
+++ b/samples/ftrace/ftrace-direct-too.c
@@ -5,14 +5,14 @@
 #include <linux/ftrace.h>
 #include <asm/asm-offsets.h>
 
-extern void my_direct_func(struct vm_area_struct *vma,
-			   unsigned long address, unsigned int flags);
+extern void my_direct_func(struct vm_area_struct *vma, unsigned long address,
+			   unsigned int flags, struct pt_regs *regs);
 
-void my_direct_func(struct vm_area_struct *vma,
-			unsigned long address, unsigned int flags)
+void my_direct_func(struct vm_area_struct *vma, unsigned long address,
+		    unsigned int flags, struct pt_regs *regs)
 {
-	trace_printk("handle mm fault vma=%p address=%lx flags=%x\n",
-		     vma, address, flags);
+	trace_printk("handle mm fault vma=%p address=%lx flags=%x regs=%p\n",
+		     vma, address, flags, regs);
 }
 
 extern void my_tramp(void *);
@@ -34,7 +34,9 @@ asm (
 "	pushq %rdi\n"
 "	pushq %rsi\n"
 "	pushq %rdx\n"
+"	pushq %rcx\n"
 "	call my_direct_func\n"
+"	popq %rcx\n"
 "	popq %rdx\n"
 "	popq %rsi\n"
 "	popq %rdi\n"
-- 
2.40.0.577.gac1e443424-goog