Re: [RFC PATCH v1 1/1] tracing/kprobes: Return ENAMESVRLSYMS when func matches several symbols

Francis Laniel
2023-08-24T10:40:23Z

Hi.

Le jeudi 24 août 2023, 01:53:55 CEST Masami Hiramatsu a écrit :
> Hi Francis,
>
> On Wed, 23 Aug 2023 18:14:10 +0200
>
> Francis Laniel <flaniel@linux.microsoft.com> wrote:
> > Previously to this commit, if func matches several symbols, a PMU kprobe
> > would be installed for the first matching address.
> > This could lead to some misunderstanding when some BPF code was never
> > called because it was attached to a function which was indeed not call,
> > because the effectively called one has no kprobes.
> >
> > So, this commit introduces ENAMESVRLSYMS which is returned when func
> > matches several symbols.
>
> The trace_kprobe part looks good to me.
> But sorry, I mislead you. I meant using an existing error code as a
> metaphor. EINVAL is used everywhere, so choose another error code, e.g.
> EADDRNOTAVAIL.

No problem, I was a bit in doubt regarding adding a new error code, but at
least I learnt how to do it if one day I need to do so!
But yes, for this case, better to use an existing one!

> Also, can you add this check in __trace_kprobe_create()?
> I think right before below code, at that point, 'symbol' has the symbol
> name.
>
> trace_probe_log_set_index(0);
> if (event) {
> ret = traceprobe_parse_event_name(&event, &group, gbuf,
> event - argv[0]);
> if (ret)
> goto parse_error;
> }

Addressed in v2, thank you!

>
> Thank you,
>
> > This way, user needs to use addr to remove the ambiguity.
> >
> > Suggested-by: Masami Hiramatsu <mhiramat@kernel.org>
> > Signed-off-by: Francis Laniel <flaniel@linux.microsoft.com>
> > Link:
> > https://lore.kernel.org/lkml/20230819101105.b0c104ae4494a7d1f2eea742@kern
> > el.org/ ---
> >
> > arch/alpha/include/uapi/asm/errno.h | 2 ++
> > arch/mips/include/uapi/asm/errno.h | 2 ++
> > arch/parisc/include/uapi/asm/errno.h | 2 ++
> > arch/sparc/include/uapi/asm/errno.h | 2 ++
> > include/uapi/asm-generic/errno.h | 2 ++
> > kernel/trace/trace_kprobe.c | 26 ++++++++++++++++++++++
> > tools/arch/alpha/include/uapi/asm/errno.h | 2 ++
> > tools/arch/mips/include/uapi/asm/errno.h | 2 ++
> > tools/arch/parisc/include/uapi/asm/errno.h | 2 ++
> > tools/arch/sparc/include/uapi/asm/errno.h | 2 ++
> > tools/include/uapi/asm-generic/errno.h | 2 ++
> > 11 files changed, 46 insertions(+)
> >
> > diff --git a/arch/alpha/include/uapi/asm/errno.h
> > b/arch/alpha/include/uapi/asm/errno.h index 3d265f6babaf..3d9686d915f9
> > 100644
> > --- a/arch/alpha/include/uapi/asm/errno.h
> > +++ b/arch/alpha/include/uapi/asm/errno.h
> > @@ -125,4 +125,6 @@
> >
> > #define EHWPOISON 139 /* Memory page has hardware error */
> >
> > +#define ENAMESVRLSYMS 140 /* Name correspond to several symbols */
> > +
> >
> > #endif
> >
> > diff --git a/arch/mips/include/uapi/asm/errno.h
> > b/arch/mips/include/uapi/asm/errno.h index 2fb714e2d6d8..1fd64ee7b629
> > 100644
> > --- a/arch/mips/include/uapi/asm/errno.h
> > +++ b/arch/mips/include/uapi/asm/errno.h
> > @@ -124,6 +124,8 @@
> >
> > #define EHWPOISON 168 /* Memory page has hardware error */
> >
> > +#define ENAMESVRLSYMS 169 /* Name correspond to several symbols */
> > +
> >
> > #define EDQUOT 1133 /* Quota exceeded */
> >
> > diff --git a/arch/parisc/include/uapi/asm/errno.h
> > b/arch/parisc/include/uapi/asm/errno.h index 87245c584784..c7845ceece26
> > 100644
> > --- a/arch/parisc/include/uapi/asm/errno.h
> > +++ b/arch/parisc/include/uapi/asm/errno.h
> > @@ -124,4 +124,6 @@
> >
> > #define EHWPOISON 257 /* Memory page has hardware error */
> >
> > +#define ENAMESVRLSYMS 258 /* Name correspond to several symbols */
> > +
> >
> > #endif
> >
> > diff --git a/arch/sparc/include/uapi/asm/errno.h
> > b/arch/sparc/include/uapi/asm/errno.h index 81a732b902ee..1ed065943bab
> > 100644
> > --- a/arch/sparc/include/uapi/asm/errno.h
> > +++ b/arch/sparc/include/uapi/asm/errno.h
> > @@ -115,4 +115,6 @@
> >
> > #define EHWPOISON 135 /* Memory page has hardware error */
> >
> > +#define ENAMESVRLSYMS 136 /* Name correspond to several symbols */
> > +
> >
> > #endif
> >
> > diff --git a/include/uapi/asm-generic/errno.h
> > b/include/uapi/asm-generic/errno.h index cf9c51ac49f9..3d5d5740c8da
> > 100644
> > --- a/include/uapi/asm-generic/errno.h
> > +++ b/include/uapi/asm-generic/errno.h
> > @@ -120,4 +120,6 @@
> >
> > #define EHWPOISON 133 /* Memory page has hardware error */
> >
> > +#define ENAMESVRLSYMS 134 /* Name correspond to several symbols */
> > +
> >
> > #endif
> >
> > diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> > index 23dba01831f7..53b66db1ff53 100644
> > --- a/kernel/trace/trace_kprobe.c
> > +++ b/kernel/trace/trace_kprobe.c
> > @@ -1699,6 +1699,16 @@ static int unregister_kprobe_event(struct
> > trace_kprobe *tk)>
> > }
> >
> > #ifdef CONFIG_PERF_EVENTS
> >
> > +
> > +static int count_symbols(void *data, unsigned long unused)
> > +{
> > + unsigned int *count = data;
> > +
> > + (*count)++;
> > +
> > + return 0;
> > +}
> > +
> >
> > /* create a trace_kprobe, but don't add it to global lists */
> > struct trace_event_call *
> > create_local_trace_kprobe(char *func, void *addr, unsigned long offs,
> >
> > @@ -1709,6 +1719,22 @@ create_local_trace_kprobe(char *func, void *addr,
> > unsigned long offs,>
> > int ret;
> > char *event;
> >
> > + /*
> > + * If user specifies func, we check that the function name does not
> > + * correspond to several symbols.
> > + * If this is the case, we return with error code ENAMESVRLSYMS to
> > + * indicate the user he/she should use addr and offs rather than func
to
> > + * remove the ambiguity.
> > + */
> > + if (func) {
> > + unsigned int count;
> > +
> > + count = 0;
> > + kallsyms_on_each_match_symbol(count_symbols, func, &count);
> > + if (count > 1)
> > + return ERR_PTR(-ENAMESVRLSYMS);
> > + }
> > +
> >
> > /*
> >
> > * local trace_kprobes are not added to dyn_event, so they are never
> > * searched in find_trace_kprobe(). Therefore, there is no concern of
> >
> > diff --git a/tools/arch/alpha/include/uapi/asm/errno.h
> > b/tools/arch/alpha/include/uapi/asm/errno.h index
> > 3d265f6babaf..3d9686d915f9 100644
> > --- a/tools/arch/alpha/include/uapi/asm/errno.h
> > +++ b/tools/arch/alpha/include/uapi/asm/errno.h
> > @@ -125,4 +125,6 @@
> >
> > #define EHWPOISON 139 /* Memory page has hardware error */
> >
> > +#define ENAMESVRLSYMS 140 /* Name correspond to several symbols */
> > +
> >
> > #endif
> >
> > diff --git a/tools/arch/mips/include/uapi/asm/errno.h
> > b/tools/arch/mips/include/uapi/asm/errno.h index
> > 2fb714e2d6d8..1fd64ee7b629 100644
> > --- a/tools/arch/mips/include/uapi/asm/errno.h
> > +++ b/tools/arch/mips/include/uapi/asm/errno.h
> > @@ -124,6 +124,8 @@
> >
> > #define EHWPOISON 168 /* Memory page has hardware error */
> >
> > +#define ENAMESVRLSYMS 169 /* Name correspond to several symbols */
> > +
> >
> > #define EDQUOT 1133 /* Quota exceeded */
> >
> > diff --git a/tools/arch/parisc/include/uapi/asm/errno.h
> > b/tools/arch/parisc/include/uapi/asm/errno.h index
> > 87245c584784..c7845ceece26 100644
> > --- a/tools/arch/parisc/include/uapi/asm/errno.h
> > +++ b/tools/arch/parisc/include/uapi/asm/errno.h
> > @@ -124,4 +124,6 @@
> >
> > #define EHWPOISON 257 /* Memory page has hardware error */
> >
> > +#define ENAMESVRLSYMS 258 /* Name correspond to several symbols */
> > +
> >
> > #endif
> >
> > diff --git a/tools/arch/sparc/include/uapi/asm/errno.h
> > b/tools/arch/sparc/include/uapi/asm/errno.h index
> > 81a732b902ee..1ed065943bab 100644
> > --- a/tools/arch/sparc/include/uapi/asm/errno.h
> > +++ b/tools/arch/sparc/include/uapi/asm/errno.h
> > @@ -115,4 +115,6 @@
> >
> > #define EHWPOISON 135 /* Memory page has hardware error */
> >
> > +#define ENAMESVRLSYMS 136 /* Name correspond to several symbols */
> > +
> >
> > #endif
> >
> > diff --git a/tools/include/uapi/asm-generic/errno.h
> > b/tools/include/uapi/asm-generic/errno.h index cf9c51ac49f9..3d5d5740c8da
> > 100644
> > --- a/tools/include/uapi/asm-generic/errno.h
> > +++ b/tools/include/uapi/asm-generic/errno.h
> > @@ -120,4 +120,6 @@
> >
> > #define EHWPOISON 133 /* Memory page has hardware error */
> >
> > +#define ENAMESVRLSYMS 134 /* Name correspond to several symbols */
> > +
> >
> > #endif
> >
> > --
> > 2.34.1

Best regards.