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Date: Tue, 26 Apr 2022 19:01:08 +0900
From: Masami Hiramatsu <mhiramat@...nel.org>
To: Jiri Olsa <olsajiri@...il.com>
Cc: Jiri Olsa <jolsa@...nel.org>, Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Andrii Nakryiko <andrii@...nel.org>, netdev@...r.kernel.org,
bpf@...r.kernel.org, lkml <linux-kernel@...r.kernel.org>,
Martin KaFai Lau <kafai@...com>,
Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
John Fastabend <john.fastabend@...il.com>,
KP Singh <kpsingh@...omium.org>
Subject: Re: [PATCHv2 bpf-next 1/4] kallsyms: Add kallsyms_lookup_names
function
Hi Jiri,
Sorry for replying late.
On Fri, 22 Apr 2022 08:47:13 +0200
Jiri Olsa <olsajiri@...il.com> wrote:
> On Tue, Apr 19, 2022 at 10:26:05AM +0200, Jiri Olsa wrote:
>
> SNIP
>
> > > > +static int kallsyms_callback(void *data, const char *name,
> > > > + struct module *mod, unsigned long addr)
> > > > +{
> > > > + struct kallsyms_data *args = data;
> > > > +
> > > > + if (!bsearch(&name, args->syms, args->cnt, sizeof(*args->syms), symbols_cmp))
> > > > + return 0;
> > > > +
> > > > + addr = ftrace_location(addr);
> > > > + if (!addr)
> > > > + return 0;
> > >
> > > Ooops, wait. Did you do this last version? I missed this point.
> > > This changes the meanings of the kernel function.
> >
> > yes, it was there before ;-) and you're right.. so some archs can
> > return different address, I did not realize that
> >
> > >
> > > > +
> > > > + args->addrs[args->found++] = addr;
> > > > + return args->found == args->cnt ? 1 : 0;
> > > > +}
> > > > +
> > > > +/**
> > > > + * kallsyms_lookup_names - Lookup addresses for array of symbols
> > >
> > > More correctly "Lookup 'ftraced' addresses for array of sorted symbols", right?
> > >
> > > I'm not sure, we can call it as a 'kallsyms' API, since this is using
> > > kallsyms but doesn't return symbol address, but ftrace address.
> > > I think this name misleads user to expect returning symbol address.
> > >
> > > > + *
> > > > + * @syms: array of symbols pointers symbols to resolve, must be
> > > > + * alphabetically sorted
> > > > + * @cnt: number of symbols/addresses in @syms/@...rs arrays
> > > > + * @addrs: array for storing resulting addresses
> > > > + *
> > > > + * This function looks up addresses for array of symbols provided in
> > > > + * @syms array (must be alphabetically sorted) and stores them in
> > > > + * @addrs array, which needs to be big enough to store at least @cnt
> > > > + * addresses.
> > >
> > > Hmm, sorry I changed my mind. I rather like to expose kallsyms_on_each_symbol()
> > > and provide this API from fprobe or ftrace, because this returns ftrace address
> > > and thus this is only used from fprobe.
> >
> > ok, so how about:
> >
> > int ftrace_lookup_symbols(const char **sorted_syms, size_t cnt, unsigned long *addrs);
>
> quick question.. is it ok if it stays in kalsyms.c object?
I think if this is for the ftrace API, I think it should be in the ftrace.c, and
it can remove unneeded #ifdefs in C code.
>
> so we don't need to expose kallsyms_on_each_symbol,
> and it stays in 'kalsyms' place
We don't need to expose it to modules, but just make it into a global scope.
I don't think that doesn't cause a problem.
Thank you,
>
> jirka
>
>
>
> diff --git a/include/linux/kallsyms.h b/include/linux/kallsyms.h
> index ce1bd2fbf23e..177e0b13c8c5 100644
> --- a/include/linux/kallsyms.h
> +++ b/include/linux/kallsyms.h
> @@ -72,6 +72,7 @@ int kallsyms_on_each_symbol(int (*fn)(void *, const char *, struct module *,
> #ifdef CONFIG_KALLSYMS
> /* Lookup the address for a symbol. Returns 0 if not found. */
> unsigned long kallsyms_lookup_name(const char *name);
> +int ftrace_lookup_symbols(const char **sorted_syms, size_t cnt, unsigned long *addrs);
>
> extern int kallsyms_lookup_size_offset(unsigned long addr,
> unsigned long *symbolsize,
> @@ -103,6 +104,11 @@ static inline unsigned long kallsyms_lookup_name(const char *name)
> return 0;
> }
>
> +static inline int ftrace_lookup_symbols(const char **sorted_syms, size_t cnt, unsigned long *addrs);
> +{
> + return -ERANGE;
> +}
> +
> static inline int kallsyms_lookup_size_offset(unsigned long addr,
> unsigned long *symbolsize,
> unsigned long *offset)
> diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
> index 79f2eb617a62..1e7136a765a9 100644
> --- a/kernel/kallsyms.c
> +++ b/kernel/kallsyms.c
> @@ -29,6 +29,7 @@
> #include <linux/compiler.h>
> #include <linux/module.h>
> #include <linux/kernel.h>
> +#include <linux/bsearch.h>
>
> /*
> * These will be re-linked against their real values
> @@ -228,7 +229,7 @@ unsigned long kallsyms_lookup_name(const char *name)
> return module_kallsyms_lookup_name(name);
> }
>
> -#ifdef CONFIG_LIVEPATCH
> +#if defined(CONFIG_LIVEPATCH) || defined(CONFIG_FPROBE)
> /*
> * Iterate over all symbols in vmlinux. For symbols from modules use
> * module_kallsyms_on_each_symbol instead.
> @@ -572,6 +573,73 @@ int sprint_backtrace_build_id(char *buffer, unsigned long address)
> return __sprint_symbol(buffer, address, -1, 1, 1);
> }
>
> +#ifdef CONFIG_FPROBE
> +static int symbols_cmp(const void *a, const void *b)
> +{
> + const char **str_a = (const char **) a;
> + const char **str_b = (const char **) b;
> +
> + return strcmp(*str_a, *str_b);
> +}
> +
> +struct kallsyms_data {
> + unsigned long *addrs;
> + const char **syms;
> + size_t cnt;
> + size_t found;
> +};
> +
> +static int kallsyms_callback(void *data, const char *name,
> + struct module *mod, unsigned long addr)
> +{
> + struct kallsyms_data *args = data;
> +
> + if (!bsearch(&name, args->syms, args->cnt, sizeof(*args->syms), symbols_cmp))
> + return 0;
> +
> + addr = ftrace_location(addr);
> + if (!addr)
> + return 0;
> +
> + args->addrs[args->found++] = addr;
> + return args->found == args->cnt ? 1 : 0;
> +}
> +
> +/**
> + * ftrace_lookup_symbols - Lookup addresses for array of symbols
> + *
> + * @sorted_syms: array of symbols pointers symbols to resolve,
> + * must be alphabetically sorted
> + * @cnt: number of symbols/addresses in @syms/@...rs arrays
> + * @addrs: array for storing resulting addresses
> + *
> + * This function looks up addresses for array of symbols provided in
> + * @syms array (must be alphabetically sorted) and stores them in
> + * @addrs array, which needs to be big enough to store at least @cnt
> + * addresses.
> + *
> + * This function returns 0 if all provided symbols are found,
> + * -ESRCH otherwise.
> + */
> +int ftrace_lookup_symbols(const char **sorted_syms, size_t cnt, unsigned long *addrs)
> +{
> + struct kallsyms_data args;
> +
> + args.addrs = addrs;
> + args.syms = sorted_syms;
> + args.cnt = cnt;
> + args.found = 0;
> + kallsyms_on_each_symbol(kallsyms_callback, &args);
> +
> + return args.found == args.cnt ? 0 : -ESRCH;
> +}
> +#else
> +int ftrace_lookup_symbols(const char **sorted_syms, size_t cnt, unsigned long *addrs)
> +{
> + return -ERANGE;
> +}
> +#endif /* CONFIG_FPROBE */
> +
> /* To avoid using get_symbol_offset for every symbol, we carry prefix along. */
> struct kallsym_iter {
> loff_t pos;
--
Masami Hiramatsu <mhiramat@...nel.org>
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