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Tue, 18 Nov 2025 14:01:58 -0800 (PST) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Tue, 18 Nov 2025 23:01:56 +0100 To: Menglong Dong Cc: ast@kernel.org, rostedt@goodmis.org, daniel@iogearbox.net, john.fastabend@gmail.com, andrii@kernel.org, martin.lau@linux.dev, eddyz87@gmail.com, song@kernel.org, yonghong.song@linux.dev, kpsingh@kernel.org, sdf@fomichev.me, haoluo@google.com, mhiramat@kernel.org, mark.rutland@arm.com, mathieu.desnoyers@efficios.com, jiang.biao@linux.dev, bpf@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org Subject: Re: [PATCH bpf-next v3 2/6] x86/ftrace: implement DYNAMIC_FTRACE_WITH_JMP Message-ID: References: <20251118123639.688444-1-dongml2@chinatelecom.cn> <20251118123639.688444-3-dongml2@chinatelecom.cn> Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251118123639.688444-3-dongml2@chinatelecom.cn> On Tue, Nov 18, 2025 at 08:36:30PM +0800, Menglong Dong wrote: > Implement the DYNAMIC_FTRACE_WITH_JMP for x86_64. In ftrace_call_replace, > we will use JMP32_INSN_OPCODE instead of CALL_INSN_OPCODE if the address > should use "jmp". > > Meanwhile, adjust the direct call in the ftrace_regs_caller. The RSB is > balanced in the "jmp" mode. Take the function "foo" for example: > > original_caller: > call foo -> foo: > call fentry -> fentry: > [do ftrace callbacks ] > move tramp_addr to stack > RET -> tramp_addr > tramp_addr: > [..] > call foo_body -> foo_body: > [..] > RET -> back to tramp_addr > [..] > RET -> back to original_caller > > Signed-off-by: Menglong Dong > --- > arch/x86/Kconfig | 1 + > arch/x86/kernel/ftrace.c | 7 ++++++- > arch/x86/kernel/ftrace_64.S | 12 +++++++++++- > 3 files changed, 18 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig > index fa3b616af03a..462250a20311 100644 > --- a/arch/x86/Kconfig > +++ b/arch/x86/Kconfig > @@ -230,6 +230,7 @@ config X86 > select HAVE_DYNAMIC_FTRACE_WITH_ARGS if X86_64 > select HAVE_FTRACE_REGS_HAVING_PT_REGS if X86_64 > select HAVE_DYNAMIC_FTRACE_WITH_DIRECT_CALLS > + select HAVE_DYNAMIC_FTRACE_WITH_JMP if X86_64 > select HAVE_SAMPLE_FTRACE_DIRECT if X86_64 > select HAVE_SAMPLE_FTRACE_DIRECT_MULTI if X86_64 > select HAVE_EBPF_JIT > diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c > index 4450acec9390..0543b57f54ee 100644 > --- a/arch/x86/kernel/ftrace.c > +++ b/arch/x86/kernel/ftrace.c > @@ -74,7 +74,12 @@ static const char *ftrace_call_replace(unsigned long ip, unsigned long addr) > * No need to translate into a callthunk. The trampoline does > * the depth accounting itself. > */ > - return text_gen_insn(CALL_INSN_OPCODE, (void *)ip, (void *)addr); > + if (ftrace_is_jmp(addr)) { > + addr = ftrace_jmp_get(addr); > + return text_gen_insn(JMP32_INSN_OPCODE, (void *)ip, (void *)addr); > + } else { > + return text_gen_insn(CALL_INSN_OPCODE, (void *)ip, (void *)addr); > + } > } > > static int ftrace_verify_code(unsigned long ip, const char *old_code) > diff --git a/arch/x86/kernel/ftrace_64.S b/arch/x86/kernel/ftrace_64.S > index 823dbdd0eb41..a132608265f6 100644 > --- a/arch/x86/kernel/ftrace_64.S > +++ b/arch/x86/kernel/ftrace_64.S > @@ -285,8 +285,18 @@ SYM_INNER_LABEL(ftrace_regs_caller_end, SYM_L_GLOBAL) > ANNOTATE_NOENDBR > RET > > +1: > + testb $1, %al > + jz 2f > + andq $0xfffffffffffffffe, %rax > + movq %rax, MCOUNT_REG_SIZE+8(%rsp) > + restore_mcount_regs > + /* Restore flags */ > + popfq > + RET is this hunk the reason for the 0x1 jmp-bit you set in the address? I wonder if we introduced new flag in dyn_ftrace::flags for this, then we'd need to have extra ftrace trampoline for jmp ftrace_ops jirka