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

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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 <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Will Deacon 2020-05-18 14:01:01 +01:00
parent 871e100e43
commit 258c3d628f
1 changed files with 3 additions and 2 deletions
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5
arch/arm64/kernel/entry-ftrace.S
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@ -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