linux-kernel - Re: [PATCH v16 04/18] function_graph: Replace fgraph_ret_regs with ftrace

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Message-Id: <20241021132223.e3841b01cb8b449b66ebbb44@kernel.org>
Date: Mon, 21 Oct 2024 13:22:23 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Heiko Carstens <hca@...ux.ibm.com>
Cc: Alexei Starovoitov <alexei.starovoitov@...il.com>, Steven Rostedt
 <rostedt@...dmis.org>, Florent Revest <revest@...omium.org>,
 linux-trace-kernel@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
 Martin KaFai Lau <martin.lau@...ux.dev>, bpf <bpf@...r.kernel.org>, Alexei
 Starovoitov <ast@...nel.org>, Jiri Olsa <jolsa@...nel.org>, Alan Maguire
 <alan.maguire@...cle.com>, Mark Rutland <mark.rutland@....com>,
 linux-arch@...r.kernel.org, Catalin Marinas <catalin.marinas@....com>, Will
 Deacon <will@...nel.org>, Huacai Chen <chenhuacai@...nel.org>, WANG Xuerui
 <kernel@...0n.name>, Paul Walmsley <paul.walmsley@...ive.com>, Palmer
 Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, Vasily
 Gorbik <gor@...ux.ibm.com>, Alexander Gordeev <agordeev@...ux.ibm.com>,
 Christian Borntraeger <borntraeger@...ux.ibm.com>, Sven Schnelle
 <svens@...ux.ibm.com>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar
 <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, Dave Hansen
 <dave.hansen@...ux.intel.com>, x86@...nel.org, "H. Peter Anvin"
 <hpa@...or.com>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: Re: [PATCH v16 04/18] function_graph: Replace fgraph_ret_regs with
 ftrace_regs

On Wed, 16 Oct 2024 10:33:23 +0200
Heiko Carstens <hca@...ux.ibm.com> wrote:

> On Wed, Oct 16, 2024 at 08:47:20AM +0900, Masami Hiramatsu wrote:
> > On Tue, 15 Oct 2024 20:39:06 +0200
> > Heiko Carstens <hca@...ux.ibm.com> wrote:
> > 
> > > That would make things much simpler... e.g. your new patch is also
> > > writing r3 to fregs, why? 
> > 
> > BTW, according to the document [1], r3 is for "return value 1", isn't it
> > used usually?
> > 
> > [1] https://www.kernel.org/doc/Documentation/s390/Debugging390.txt
> 
> That is true for the 32 bit ABI, but not for the 64 bit ABI which we
> care about. Besides other this is also the reason why I removed the
> above file five years ago: f62f7dcbf023 ("Documentation/s390: remove
> outdated debugging390 documentation").
> 
> If you really want to understand the 64 bit s390 ABI then you need to
> look at https://github.com/IBM/s390x-abi .
> 
> A PDF file of the latest release is available at
> https://github.com/IBM/s390x-abi/releases/download/v1.6.1/lzsabi_s390x.pdf
> 
> See section "1.2.5. Return Values" for return value handling.

Ah, these are the info what I searched!

> 
> All of that said, I would appreciate if you would just merge the
> provided patch, unless there is a reason for not doing that. Chances
> are that I missed something with all the recent fregs vs ptregs
> changes.

OK

Thanks!

-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>