Subject: Re: [PATCH 13/15] perf tools: Synthesize bpf_trampoline/dispatcher ksymbol event

From: Arnaldo Carvalho de Melo <[email-masked]>
Date: Mon, 6 Apr 2020 09:54:12 -0300

Em Thu, Mar 12, 2020 at 08:56:08PM +0100, Jiri Olsa escreveu:
> +static int
> +process_bpf_image(char *name, u64 addr, struct kallsyms_parse *data)
> +{
> +	struct machine *machine = data->machine;
> +	union perf_event *event = data->event;
> +	struct perf_record_ksymbol *ksymbol;
> +
> +	ksymbol = &event->ksymbol;
> +
> +	*ksymbol = (struct perf_record_ksymbol) {
> +		.header = {
> +			.type = PERF_RECORD_KSYMBOL,
> +			.size = offsetof(struct perf_record_ksymbol, name),
> +		},
> +		.addr      = addr,
> +		.len       = page_size,
> +		.ksym_type = PERF_RECORD_KSYMBOL_TYPE_BPF,
> +		.flags     = 0,
> +	};
> +
> +	strncpy(ksymbol->name, name, KSYM_NAME_LEN);
> +	ksymbol->header.size += PERF_ALIGN(strlen(name) + 1, sizeof(u64));
> +	memset((void *) event + event->header.size, 0, machine->id_hdr_size);
> +	event->header.size += machine->id_hdr_size;
> +
> +	return perf_tool__process_synth_event(data->tool, event, machine,
> +					      data->process);

This explodes in fedora 32 and rawhide and in openmandriva:cooker:

  GEN      /tmp/build/perf/python/perf.so
  CC       /tmp/build/perf/util/bpf-event.o
In file included from /usr/include/string.h:495,
                 from /git/perf/tools/lib/bpf/libbpf_common.h:12,
                 from /git/perf/tools/lib/bpf/bpf.h:31,
                 from util/bpf-event.c:4:
In function ‘strncpy’,
    inlined from ‘process_bpf_image’ at util/bpf-event.c:323:2,
    inlined from ‘kallsyms_process_symbol’ at util/bpf-event.c:358:9:
/usr/include/bits/string_fortified.h:106:10: error: ‘__builtin_strncpy’ specified bound 256 equals destination size [-Werror=stringop-truncation]
  106 |   return __builtin___strncpy_chk (__dest, __src, __len, __bos (__dest));
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors
mv: cannot stat '/tmp/build/perf/util/.bpf-event.o.tmp': No such file or directory
make[4]: *** [/git/perf/tools/build/Makefile.build:97: /tmp/build/perf/util/bpf-event.o] Error 1
make[3]: *** [/git/perf/tools/build/Makefile.build:139: util] Error 2
make[2]: *** [Makefile.perf:617: /tmp/build/perf/perf-in.o] Error 2
make[1]: *** [Makefile.perf:225: sub-make] Error 2
make: *** [Makefile:70: all] Error 2
make: Leaving directory '/git/perf/tools/perf'
[perfbuilder@fc58e82bfba4 ~]$

So I patched it a bit, please ack:

diff --git a/tools/perf/util/bpf-event.c b/tools/perf/util/bpf-event.c
index 3728db98981e..0cd41a862952 100644
--- a/tools/perf/util/bpf-event.c
+++ b/tools/perf/util/bpf-event.c
@@ -306,6 +306,7 @@ process_bpf_image(char *name, u64 addr, struct kallsyms_parse *data)
 	struct machine *machine = data->machine;
 	union perf_event *event = data->event;
 	struct perf_record_ksymbol *ksymbol;
+	int len;
 
 	ksymbol = &event->ksymbol;
 
@@ -320,8 +321,8 @@ process_bpf_image(char *name, u64 addr, struct kallsyms_parse *data)
 		.flags     = 0,
 	};
 
-	strncpy(ksymbol->name, name, KSYM_NAME_LEN);
-	ksymbol->header.size += PERF_ALIGN(strlen(name) + 1, sizeof(u64));
+	len = scnprintf(ksymbol->name, KSYM_NAME_LEN, "%s", name);
+	ksymbol->header.size += PERF_ALIGN(len + 1, sizeof(u64));
 	memset((void *) event + event->header.size, 0, machine->id_hdr_size);
 	event->header.size += machine->id_hdr_size;