On Fri, Apr 08, 2022 at 04:19:25PM -0700, Alexei Starovoitov wrote:
> On Thu, Apr 07, 2022 at 02:52:21PM +0200, Jiri Olsa wrote:
> > Adding kallsyms_lookup_names function that resolves array of symbols
> > with single pass over kallsyms.
> >
> > The user provides array of string pointers with count and pointer to
> > allocated array for resolved values.
> >
> > int kallsyms_lookup_names(const char **syms, u32 cnt,
> > unsigned long *addrs)
> >
> > Before we iterate kallsyms we sort user provided symbols by name and
> > then use that in kalsyms iteration to find each kallsyms symbol in
> > user provided symbols.
> >
> > We also check each symbol to pass ftrace_location, because this API
> > will be used for fprobe symbols resolving. This can be optional in
> > future if there's a need.
> >
> > Suggested-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
> > Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> > ---
> > include/linux/kallsyms.h | 6 +++++
> > kernel/kallsyms.c | 48 ++++++++++++++++++++++++++++++++++++++++
> > 2 files changed, 54 insertions(+)
> >
> > diff --git a/include/linux/kallsyms.h b/include/linux/kallsyms.h
> > index ce1bd2fbf23e..5320a5e77f61 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 kallsyms_lookup_names(const char **syms, u32 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;
> > }
> >
> > +int kallsyms_lookup_names(const char **syms, u32 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..a3738ddf9e87 100644
> > --- a/kernel/kallsyms.c
> > +++ b/kernel/kallsyms.c
> > @@ -29,6 +29,8 @@
> > #include <linux/compiler.h>
> > #include <linux/module.h>
> > #include <linux/kernel.h>
> > +#include <linux/bsearch.h>
> > +#include <linux/sort.h>
> >
> > /*
> > * These will be re-linked against their real values
> > @@ -572,6 +574,52 @@ int sprint_backtrace_build_id(char *buffer, unsigned long address)
> > return __sprint_symbol(buffer, address, -1, 1, 1);
> > }
> >
> > +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;
> > + u32 cnt;
> > + u32 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;
> > +}
> > +
> > +int kallsyms_lookup_names(const char **syms, u32 cnt, unsigned long *addrs)
> > +{
> > + struct kallsyms_data args;
> > +
> > + sort(syms, cnt, sizeof(*syms), symbols_cmp, NULL);
>
> It's nice to share symbols_cmp for sort and bsearch,
> but messing technically input argument 'syms' like this will cause
> issues sooner or later.
> Lets make caller do the sort.
> Unordered input will cause issue with bsearch, of course,
> but it's a lesser evil. imo.
ok, will move it out and make some proper comment for the
function mentioning the sort requirement for syms
thanks,
jirka
>
> > +
> > + args.addrs = addrs;
> > + args.syms = syms;
> > + args.cnt = cnt;
> > + args.found = 0;
> > + kallsyms_on_each_symbol(kallsyms_callback, &args);
> > +
> > + return args.found == args.cnt ? 0 : -EINVAL;
> > +}
> > +
> > /* To avoid using get_symbol_offset for every symbol, we carry prefix along. */
> > struct kallsym_iter {
> > loff_t pos;
> > --
> > 2.35.1
> >
