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

-----Original Message-----
From: Leo Yan <redacted>
Sent: Tuesday, February 9, 2021 8:17 PM
To: Jianlin Lv <redacted>
Cc: john.garry@huawei.com; will@kernel.org; mathieu.poirier@linaro.org;
peterz@infradead.org; mingo@redhat.com; acme@kernel.org; Mark Rutland
[off-list ref]; alexander.shishkin@linux.intel.com;
jolsa@redhat.com; namhyung@kernel.org; linux-arm-
kernel@lists.infradead.org; linux-kernel@vger.kernel.org
Subject: Re: [PATCH] perf tools: Fix arm64 build error with gcc-11

Hi Jianlin,

On Tue, Feb 09, 2021 at 07:33:57PM +0800, Jianlin Lv wrote:

quoted

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 by replacing the return
value NULL of perf_reg_name with "unknown".

Signed-off-by: Jianlin Lv <redacted>
---
 tools/perf/arch/arm64/include/perf_regs.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/perf/arch/arm64/include/perf_regs.h

b/tools/perf/arch/arm64/include/perf_regs.h
index baaa5e64a3fb..901419f907c0 100644

--- a/tools/perf/arch/arm64/include/perf_regs.h
+++ b/tools/perf/arch/arm64/include/perf_regs.h

@@ -85,10 +85,10 @@ static inline const char *perf_reg_name(int id)
 	case PERF_REG_ARM64_PC:
 		return "pc";
 	default:
-		return NULL;
+		return "unknown";
 	}

-	return NULL;
+	return "unknown";

This issue is a common issue crossing all archs.  So it's better to change the
code in the places where calls perf_reg_name(), e.g. in
util/session.c:

--- a/tools/perf/util/session.c
+++ b/tools/perf/util/session.c

@@ -1135,12 +1135,14 @@ static void branch_stack__printf(struct

perf_sample *sample, bool callstack)  static void regs_dump__printf(u64
mask, u64 *regs)  {
        unsigned rid, i = 0;
+       char *reg_name;

        for_each_set_bit(rid, (unsigned long *) &mask, sizeof(mask) * 8) {
                u64 val = regs[i++];

+               reg_name = perf_reg_name(rid);
                printf(".... %-5s 0x%016" PRIx64 "\n",
-                      perf_reg_name(rid), val);
+                      reg_name ?: "Unknown", val);
        }
 }