From: "Björn Töpel" <bjorn@kernel.org>
To: Andy Chiu <andy.chiu@sifive.com>,
Paul Walmsley <paul.walmsley@sifive.com>,
Palmer Dabbelt <palmer@dabbelt.com>,
Albert Ou <aou@eecs.berkeley.edu>,
Alexandre Ghiti <alexghiti@rivosinc.com>,
Zong Li <zong.li@sifive.com>,
Steven Rostedt <rostedt@goodmis.org>,
Masami Hiramatsu <mhiramat@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Nathan Chancellor <nathan@kernel.org>,
Nick Desaulniers <ndesaulniers@google.com>,
Bill Wendling <morbo@google.com>,
Justin Stitt <justinstitt@google.com>,
Puranjay Mohan <puranjay@kernel.org>
Cc: Palmer Dabbelt <palmer@rivosinc.com>,
linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
linux-trace-kernel@vger.kernel.org, llvm@lists.linux.dev,
Andy Chiu <andy.chiu@sifive.com>
Subject: Re: [PATCH v2 3/6] riscv: ftrace: prepare ftrace for atomic code patching
Date: Tue, 13 Aug 2024 14:59:33 +0200 [thread overview]
Message-ID: <87wmkk8toq.fsf@all.your.base.are.belong.to.us> (raw)
In-Reply-To: <20240628-dev-andyc-dyn-ftrace-v4-v2-3-1e5f4cb1f049@sifive.com>
Andy Chiu <andy.chiu@sifive.com> writes:
> We use an AUIPC+JALR pair to jump into a ftrace trampoline. Since
> instruction fetch can break down to 4 byte at a time, it is impossible
> to update two instructions without a race. In order to mitigate it, we
> initialize the patchable entry to AUIPC + NOP4. Then, the run-time code
> patching can change NOP4 to JALR to eable/disable ftrcae from a
enable ftrace
> function. This limits the reach of each ftrace entry to +-2KB displacing
> from ftrace_caller.
>
> Starting from the trampoline, we add a level of indirection for it to
> reach ftrace caller target. Now, it loads the target address from a
> memory location, then perform the jump. This enable the kernel to update
> the target atomically.
The +-2K limit is for direct calls, right?
...and this I would say breaks DIRECT_CALLS (which should be implemented
using call_ops later)?
Björn
next prev parent reply other threads:[~2024-08-13 12:59 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-06-28 11:47 [PATCH v2 0/6] riscv: ftrace: atmoic patching and preempt improvements Andy Chiu
2024-06-28 11:47 ` [PATCH v2 1/6] riscv: ftrace: support fastcc in Clang for WITH_ARGS Andy Chiu
2024-08-13 11:09 ` Björn Töpel
2024-08-22 8:39 ` Andy Chiu
2024-06-28 11:47 ` [PATCH v2 2/6] riscv: ftrace: align patchable functions to 4 Byte boundary Andy Chiu
2024-08-13 11:11 ` Björn Töpel
2024-06-28 11:47 ` [PATCH v2 3/6] riscv: ftrace: prepare ftrace for atomic code patching Andy Chiu
2024-08-13 12:59 ` Björn Töpel [this message]
2024-08-14 12:57 ` Björn Töpel
2024-09-11 10:57 ` Andy Chiu
2024-09-11 14:37 ` Björn Töpel
2024-09-11 15:03 ` Tao Chiu
2024-09-11 17:16 ` Björn Töpel
2024-06-28 11:47 ` [PATCH v2 4/6] riscv: ftrace: do not use stop_machine to update code Andy Chiu
2024-06-28 11:47 ` [PATCH v2 5/6] riscv: vector: Support calling schedule() for preemptible Vector Andy Chiu
2024-06-28 11:47 ` [PATCH v2 6/6] riscv: ftrace: support PREEMPT Andy Chiu
2024-08-13 11:00 ` [PATCH v2 0/6] riscv: ftrace: atmoic patching and preempt improvements Björn Töpel
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