[PATCH 1/2] perf tools: Fix compilation errors on gcc8

[Jiri Olsa]

We are getting following warnings on gcc8 that break compilation:

  $ make
    CC       jvmti/jvmti_agent.o
  jvmti/jvmti_agent.c: In function ‘jvmti_open’:
  jvmti/jvmti_agent.c:252:35: error: ‘/jit-’ directive output may be truncated \
    writing 5 bytes into a region of size between 1 and 4096 
[-Werror=format-truncation=]
    snprintf(dump_path, PATH_MAX, "%s/jit-%i.dump", jit_path, getpid());

There's no point in checking the result of snprintf call in
jvmti_open, the following open call will fail in case the
name is mangled or too long.

Using tool's function scnprintf that touches the return value
from the snprintf calls and thus get rid of those warnings.

  $ make DEBUG=1
    CC       arch/x86/util/perf_regs.o
  arch/x86/util/perf_regs.c: In function ‘arch_sdt_arg_parse_op’:
  arch/x86/util/perf_regs.c:229:4: error: ‘strncpy’ output truncated before 
terminating nul
  copying 2 bytes from a string of the same length [-Werror=stringop-truncation]
    strncpy(prefix, "+0", 2);
    ^~~~~~~~~~~~~~~~~~~~~~~~

Using scnprintf instead of the strncpy (which we know is safe
in here) to get rid of that warning.

Link: http://lkml.kernel.org/n/tip-sqmh28njbvm1mh6farkkt...@git.kernel.org
Signed-off-by: Jiri Olsa <jo...@kernel.org>
---
 tools/perf/arch/x86/util/perf_regs.c | 2 +-
 tools/perf/jvmti/jvmti_agent.c       | 3 ++-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/tools/perf/arch/x86/util/perf_regs.c 
b/tools/perf/arch/x86/util/perf_regs.c
index 4b2caf6d48e7..fead6b3b4206 100644
--- a/tools/perf/arch/x86/util/perf_regs.c
+++ b/tools/perf/arch/x86/util/perf_regs.c
@@ -226,7 +226,7 @@ int arch_sdt_arg_parse_op(char *old_op, char **new_op)
                else if (rm[2].rm_so != rm[2].rm_eo)
                        prefix[0] = '+';
                else
-                       strncpy(prefix, "+0", 2);
+                       scnprintf(prefix, sizeof(prefix), "+0");
        }
 
        /* Rename register */
diff --git a/tools/perf/jvmti/jvmti_agent.c b/tools/perf/jvmti/jvmti_agent.c
index 0c6d1002b524..ac1bcdc17dae 100644
--- a/tools/perf/jvmti/jvmti_agent.c
+++ b/tools/perf/jvmti/jvmti_agent.c
@@ -35,6 +35,7 @@
 #include <sys/mman.h>
 #include <syscall.h> /* for gettid() */
 #include <err.h>
+#include <linux/kernel.h>
 
 #include "jvmti_agent.h"
 #include "../util/jitdump.h"
@@ -249,7 +250,7 @@ void *jvmti_open(void)
        /*
         * jitdump file name
         */
-       snprintf(dump_path, PATH_MAX, "%s/jit-%i.dump", jit_path, getpid());
+       scnprintf(dump_path, PATH_MAX, "%s/jit-%i.dump", jit_path, getpid());
 
        fd = open(dump_path, O_CREAT|O_TRUNC|O_RDWR, 0666);
        if (fd == -1)
-- 
2.17.1