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SubjectRe: [PATCH] x86/unwind/orc: unwind ftrace trampolines with correct orc
On Thu, 18 Aug 2022 09:55:25 +0800
Chen Zhongjin <chenzhongjin@huawei.com> wrote:


> arch/x86/kernel/unwind_orc.c | 13 ++++++++-----
> 1 file changed, 8 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/kernel/unwind_orc.c b/arch/x86/kernel/unwind_orc.c
> index 38185aedf7d1..a938c5d0ed6f 100644
> --- a/arch/x86/kernel/unwind_orc.c
> +++ b/arch/x86/kernel/unwind_orc.c
> @@ -93,22 +93,25 @@ static struct orc_entry *orc_find(unsigned long ip);
> static struct orc_entry *orc_ftrace_find(unsigned long ip)
> {
> struct ftrace_ops *ops;
> - unsigned long caller;
> + unsigned long tramp_addr, offset;
>
> ops = ftrace_ops_trampoline(ip);
> if (!ops)
> return NULL;
>

Now if this is that unlikely recursion mentioned below then ops->trampoline
will be NULL, and if we do that offset addition, it will be incorrect.

Perhaps we should add here:

if (!ops->trampoline)
return NULL;


Let's add some comments.

/* Set tramp_addr to the start of the code copied by the trampoline */

> if (ops->flags & FTRACE_OPS_FL_SAVE_REGS)
> - caller = (unsigned long)ftrace_regs_call;
> + tramp_addr = (unsigned long)ftrace_regs_caller;
> else
> - caller = (unsigned long)ftrace_call;
> + tramp_addr = (unsigned long)ftrace_caller;
> +

/* Now place tramp_addr to the location within the trampoline ip is at */

> + offset = ip - ops->trampoline;
> + tramp_addr += offset;
>
> /* Prevent unlikely recursion */
> - if (ip == caller)
> + if (ip == tramp_addr)
> return NULL;
>
> - return orc_find(caller);
> + return orc_find(tramp_addr);
> }
> #else
> static struct orc_entry *orc_ftrace_find(unsigned long ip)

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