On Mon, 8 Jan 2024 15:03:21 +0000 Mark Rutland <mark.rutl...@arm.com> wrote:
> On Mon, Jan 08, 2024 at 02:21:03PM +0000, Mark Rutland wrote: > > On Mon, Jan 08, 2024 at 12:25:55PM +0000, Mark Rutland wrote: > > > We also have HAVE_FUNCTION_GRAPH_RET_ADDR_PTR, but since the return > > > address is > > > not on the stack at the point function-entry is intercepted we use the FP > > > as > > > the retp value -- in the absence of tail calls this will be different > > > between a > > > caller and callee. > > > > Ah; I just spotted that this patch changed that in ftrace_graph_func(), > > which > > is the source of the bug. > > > > As of this patch, we use the address of fregs->lr as the retp value, but the > > unwinder still uses the FP value, and so when > > unwind_recover_return_address() > > calls ftrace_graph_ret_addr(), the retp value won't match the expected > > entry on > > the fgraph ret_stack, resulting in failing to find the expected entry. > > > > Since the ftrace_regs only exist transiently during function entry/exit, > > it's > > possible for a stackframe to reuse that same address on the stack, which > > would > > result in finding a different entry by mistake. > > > > The diff below restores the existing behaviour and fixes the issue for me. > > Could you please fold that into this patch? > > > > On a separate note, looking at how this patch changed arm64's > > ftrace_graph_func(), do we need similar changes to arm64's > > prepare_ftrace_return() for the old-style mcount based ftrace? > > > > Mark. > > > > ---->8---- > > diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c > > index 205937e04ece..329092ce06ba 100644 > > --- a/arch/arm64/kernel/ftrace.c > > +++ b/arch/arm64/kernel/ftrace.c > > @@ -495,7 +495,7 @@ void ftrace_graph_func(unsigned long ip, unsigned long > > parent_ip, > > if (bit < 0) > > return; > > > > - if (!function_graph_enter_ops(*parent, ip, fregs->fp, parent, gops)) > > + if (!function_graph_enter_ops(*parent, ip, fregs->fp, (void > > *)fregs->fp, gops)) > > *parent = (unsigned long)&return_to_handler; > > > > ftrace_test_recursion_unlock(bit); > > Thinking some more, this line gets excessively long when we pass the fregs > too, > so it's probably worth adding a local variable for fp, i.e. the diff below. Yeah, that will be better to keep the line short. Thank you, > > Mark. > > ---->8---- > diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c > index 205937e04ece..d4e142ef4686 100644 > --- a/arch/arm64/kernel/ftrace.c > +++ b/arch/arm64/kernel/ftrace.c > @@ -481,8 +481,9 @@ void prepare_ftrace_return(unsigned long self_addr, > unsigned long *parent, > void ftrace_graph_func(unsigned long ip, unsigned long parent_ip, > struct ftrace_ops *op, struct ftrace_regs *fregs) > { > - unsigned long *parent = &fregs->lr; > struct fgraph_ops *gops = container_of(op, struct fgraph_ops, ops); > + unsigned long *parent = &fregs->lr; > + unsigned long fp = fregs->fp; > int bit; > > if (unlikely(ftrace_graph_is_dead())) > @@ -495,7 +496,7 @@ void ftrace_graph_func(unsigned long ip, unsigned long > parent_ip, > if (bit < 0) > return; > > - if (!function_graph_enter_ops(*parent, ip, fregs->fp, parent, gops)) > + if (!function_graph_enter_ops(*parent, ip, fp, (void *)fp, gops)) > *parent = (unsigned long)&return_to_handler; > > ftrace_test_recursion_unlock(bit); > -- Masami Hiramatsu (Google) <mhira...@kernel.org>