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Date: Wed, 6 Oct 2021 16:14:26 -0500 From: "Gustavo A. R. Silva" <gustavoars@...nel.org> To: Steven Rostedt <rostedt@...dmis.org> Cc: Ingo Molnar <mingo@...hat.com>, Daniel Bristot de Oliveira <bristot@...nel.org>, linux-kernel@...r.kernel.org, Jann Horn <jannh@...gle.com> Subject: Re: [PATCH][next] ftrace: Fix -Wcast-function-type warnings on powerpc64 On Tue, Oct 05, 2021 at 08:09:35PM -0400, Steven Rostedt wrote: > On Tue, 5 Oct 2021 14:35:57 -0500 > "Gustavo A. R. Silva" <gustavoars@...nel.org> wrote: > > > On Tue, Oct 05, 2021 at 03:08:07PM -0400, Steven Rostedt wrote: > > [..] > > > Or did you not remove your patch first? > > > > Yep; that was the problem. > > > > I now applied it to a clean tree and the warnings went away. > > > > However, I'm a bit concerned about the following Jann's comments: > > I should have replied back then, but I'll do that now (and added Jann > to the CC) > > > > > "the real issue here is that ftrace_func_t is defined as a fixed > > type, but actually has different types depending on the architecture? > > If so, it might be cleaner to define ftrace_func_t differently > > depending on architecture, or something like that?"[1] > > It's not dependent on the architecture. It's dependent on what the > architecture has implemented. There's nothing limiting the arch to use > the normal method, except that nobody implemented the updates. > > As I changed the core API, it affected the architectures, and since I > don't know how to update all the architectures that use that API, and > do not have the hardware to test it, I made it so architectures can > slowly be updated when their maintainers get time to. This was years > ago, and not much has been done. > > > > > "Would it not be possible to have two function types (#define'd as the > > same if ARCH_SUPPORTS_FTRACE_OPS), and then ensure that ftrace_func_t > > is only used as ftrace_asm_func_t if ARCH_SUPPORTS_FTRACE_OPS?"[2] > > > > "Essentially my idea here is to take the high-level rule "you can only > > directly call ftrace_func_t-typed functions from assembly if > > ARCH_SUPPORTS_FTRACE_OPS", and encode it in the type system. And then > > the compiler won't complain as long as we make sure that we never cast > > between the two types under ARCH_SUPPORTS_FTRACE_OPS==0."[3] > > > > So, is this linker approach really a good solution to this problem? :) > > > > What's the main problem with what Jann suggests? > > The main issue is I want no more #ifdef's in the main code. There's too > many already and it makes it difficult to maintain. I want to get rid > of them, not add more. So anything that adds more #ifdef's to the main > code, I will NACK. > > Which I guess leaves us with either the linker trick, or having all > the archs get updated to support the latest ftrace features, and we can > remove the current #ifdefs. OK. Are you going to apply your patch any time soon? So, I can go and enable -Wcast-function-type in my -next tree. :) Thanks -- Gustavo
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