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Tue, 27 Jul 2021 09:59:44 -0700 (PDT) Date: Tue, 27 Jul 2021 18:59:43 +0200 From: Padmanabha Srinivasaiah To: Sami Tolvanen Cc: Steven Rostedt , Ingo Molnar , Padmanabha Srinivasaiah , Nathan Chancellor , Nick Desaulniers , LKML , clang-built-linux Subject: Re: [PATCH] tracing/syscalls: Clang cfi enable syscall events Message-ID: <20210727165943.GA21786@pswork> References: <20210720221541.16164-1-padmanabha.srinivasaiah@harman.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jul 26, 2021 at 08:17:45AM -0700, Sami Tolvanen wrote: > Hi, > > On Tue, Jul 20, 2021 at 3:16 PM wrote: > > > > From: Padmanabha Srinivasaiah > > > > With clang cfi syscall symbols are appended with .cfi_jt, > > hence syscall tracer can not find corresponding syscall name. > > And results in no syscall ftrace events with CFI. > > > > To fix this issue, this introduces custom cleanup_syscall_symbol_name() > > to strip postfix ".cfi_jt" before comparing syscall and symbol name. > > > > Signed-off-by: Padmanabha Srinivasaiah > > --- > > kernel/trace/trace_syscalls.c | 22 ++++++++++++++++++++++ > > 1 file changed, 22 insertions(+) > > > > diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c > > index 8bfcd3b09422..dbc253fea34d 100644 > > --- a/kernel/trace/trace_syscalls.c > > +++ b/kernel/trace/trace_syscalls.c > > @@ -79,6 +79,27 @@ trace_get_syscall_nr(struct task_struct *task, struct pt_regs *regs) > > } > > #endif /* ARCH_TRACE_IGNORE_COMPAT_SYSCALLS */ > > > > +#if defined(CONFIG_CFI_CLANG) && defined(CONFIG_LTO_CLANG_THIN) > > +/* > > + * For a syscall symbol, clang generated non-canonical local jump tables > > + * will have entry as .cfi_jt and address of this entry > > + * will be used to replace references to the syscall symbol. > > + * so we will strip the postfix from appended symbol name. > > + */ > > +static inline bool cleanup_syscall_symbol_name(char *s) > > +{ > > + char *res; > > + > > + res = strrchr(s, '.'); > > + if (res) > > + *res = '\0'; > > + > > + return res != NULL; > > +} > > +#else > > +static inline bool cleanup_syscall_symbol_name(char *s) { return false; } > > +#endif > > + > > static __init struct syscall_metadata * > > find_syscall_meta(unsigned long syscall) > > { > > @@ -90,6 +111,7 @@ find_syscall_meta(unsigned long syscall) > > start = __start_syscalls_metadata; > > stop = __stop_syscalls_metadata; > > kallsyms_lookup(syscall, NULL, NULL, NULL, str); > > + cleanup_syscall_symbol_name(str); > > Shouldn't this happen in the kallsyms code instead? We already have > code there to clean up function names, and it seems like we should > just strip the postfix there before returning the name. > > Sami Thanks Sami for the input, yes have regenrated patch: https://lore.kernel.org/lkml/20210727140618.19130-1-treasure4paddy@gmail.com/T/#u