[PATCH v3] perf tools: Fix arm64 build error with gcc-11

[Jianlin Lv <Jianlin.Lv@arm.com>]

gcc version: 11.0.0 20210208 (experimental) (GCC)

Following build error on arm64:

.......
In function ‘printf’,
    inlined from ‘regs_dump__printf’ at util/session.c:1141:3,
    inlined from ‘regs__printf’ at util/session.c:1169:2:
/usr/include/aarch64-linux-gnu/bits/stdio2.h:107:10: \
  error: ‘%-5s’ directive argument is null [-Werror=format-overflow=]

107 |   return __printf_chk (__USE_FORTIFY_LEVEL - 1, __fmt, \
                __va_arg_pack ());

......
In function ‘fprintf’,
  inlined from ‘perf_sample__fprintf_regs.isra’ at \
    builtin-script.c:622:14:
/usr/include/aarch64-linux-gnu/bits/stdio2.h:100:10: \
    error: ‘%5s’ directive argument is null [-Werror=format-overflow=]
  100 |   return __fprintf_chk (__stream, __USE_FORTIFY_LEVEL - 1, __fmt,
  101 |                         __va_arg_pack ());

cc1: all warnings being treated as errors
.......

This patch fixes Wformat-overflow warnings. Add ternary operator,
The statement evaluates to "Unknown" if reg_name==NULL is met.

Signed-off-by: Jianlin Lv <Jianlin.Lv@arm.com>
---
v2: Add ternary operator to avoid similar errors in other arch.
v3: Declared reg_name in inner block.
---
 tools/perf/builtin-script.c                            | 4 +++-
 tools/perf/util/scripting-engines/trace-event-python.c | 3 ++-
 tools/perf/util/session.c                              | 3 ++-
 3 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/tools/perf/builtin-script.c b/tools/perf/builtin-script.c
index 42dad4a0f8cf..0d52dc45b1c7 100644
--- a/tools/perf/builtin-script.c
+++ b/tools/perf/builtin-script.c
@@ -643,7 +643,9 @@ static int perf_sample__fprintf_regs(struct regs_dump *regs, uint64_t mask,
 
 	for_each_set_bit(r, (unsigned long *) &mask, sizeof(mask) * 8) {
 		u64 val = regs->regs[i++];
-		printed += fprintf(fp, "%5s:0x%"PRIx64" ", perf_reg_name(r), val);
+		const char *reg_name = perf_reg_name(r);
+
+		printed += fprintf(fp, "%5s:0x%"PRIx64" ", reg_name ?: "unknown", val);
 	}
 
 	return printed;
diff --git a/tools/perf/util/scripting-engines/trace-event-python.c b/tools/perf/util/scripting-engines/trace-event-python.c
index c83c2c6564e0..768bdd4240f4 100644
--- a/tools/perf/util/scripting-engines/trace-event-python.c
+++ b/tools/perf/util/scripting-engines/trace-event-python.c
@@ -699,10 +699,11 @@ static int regs_map(struct regs_dump *regs, uint64_t mask, char *bf, int size)
 
 	for_each_set_bit(r, (unsigned long *) &mask, sizeof(mask) * 8) {
 		u64 val = regs->regs[i++];
+		const char *reg_name = perf_reg_name(r);
 
 		printed += scnprintf(bf + printed, size - printed,
 				     "%5s:0x%" PRIx64 " ",
-				     perf_reg_name(r), val);
+				     reg_name ?: "unknown", val);
 	}
 
 	return printed;
diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
index 25adbcce0281..2b40f1c431a3 100644
--- a/tools/perf/util/session.c
+++ b/tools/perf/util/session.c
@@ -1138,9 +1138,10 @@ static void regs_dump__printf(u64 mask, u64 *regs)
 
 	for_each_set_bit(rid, (unsigned long *) &mask, sizeof(mask) * 8) {
 		u64 val = regs[i++];
+		const char *reg_name = perf_reg_name(rid);
 
 		printf(".... %-5s 0x%016" PRIx64 "\n",
-		       perf_reg_name(rid), val);
+		       reg_name ?: "unknown", val);
 	}
 }
 
-- 
2.25.1