arm64: entry-ftrace.S: Update comment to indicate that x18 is live

willdeacon · willdeacon · commit 258c3d628fe9 · 2020-05-18T17:47:50.000+01:00
The Shadow Call Stack pointer is held in x18, so update the ftrace
entry comment to indicate that it cannot be safely clobbered.

Reported-by: Mark Rutland &lt;mark.rutland@arm.com&gt;
Signed-off-by: Will Deacon &lt;will@kernel.org&gt;
diff --git a/arch/arm64/kernel/entry-ftrace.S b/arch/arm64/kernel/entry-ftrace.S
@@ -23,8 +23,9 @@
  *
  * ... where <entry> is either ftrace_caller or ftrace_regs_caller.
  *
- * Each instrumented function follows the AAPCS, so here x0-x8 and x19-x30 are
- * live, and x9-x18 are safe to clobber.
+ * Each instrumented function follows the AAPCS, so here x0-x8 and x18-x30 are
+ * live (x18 holds the Shadow Call Stack pointer), and x9-x17 are safe to
+ * clobber.
  *
  * We save the callsite's context into a pt_regs before invoking any ftrace
  * callbacks. So that we can get a sensible backtrace, we create a stack record

Original file line number	Diff line number	Diff line change
`@@ -23,8 +23,9 @@`
`23`	`23`	`*`
`24`	`24`	`* ... where <entry> is either ftrace_caller or ftrace_regs_caller.`
`25`	`25`	`*`
`26`		`- * Each instrumented function follows the AAPCS, so here x0-x8 and x19-x30 are`
`27`		`- * live, and x9-x18 are safe to clobber.`
	`26`	`+ * Each instrumented function follows the AAPCS, so here x0-x8 and x18-x30 are`
	`27`	`+ * live (x18 holds the Shadow Call Stack pointer), and x9-x17 are safe to`
	`28`	`+ * clobber.`
`28`	`29`	`*`
`29`	`30`	`* We save the callsite's context into a pt_regs before invoking any ftrace`
`30`	`31`	`* callbacks. So that we can get a sensible backtrace, we create a stack record`