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From:   Tiezhu Yang <yangtiezhu@loongson.cn>
To:     Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@redhat.com>,
        Namhyung Kim <namhyung@kernel.org>
Cc:     linux-kernel@vger.kernel.org, Xuefeng Li <lixuefeng@loongson.cn>
Subject: [PATCH] perf callchain: Return directly when use '--call-graph dwarf' under !CONFIG_DWARF
Date:   Mon, 14 Dec 2020 20:56:55 +0800
Message-Id: <1607950615-11825-1-git-send-email-yangtiezhu@loongson.cn>
Precedence: bulk

DWARF register mappings have not been defined for some architectures,
at least for mips, so we can print an error message and then return
directly when use '--call-graph dwarf'.

E.g. without this patch:

[root@linux perf]# ./perf record --call-graph dwarf cd
Error:
The sys_perf_event_open() syscall returned with 89 (Function not implemented) for event (cycles).
/bin/dmesg | grep -i perf may provide additional information.

With this patch:

[root@linux perf]# ./perf record --call-graph dwarf cd
DWARF is not supported for architecture mips64

 Usage: perf record [<options>] [<command>]
    or: perf record [<options>] -- <command> [<options>]

        --call-graph <record_mode[,record_size]>
                          setup and enables call-graph (stack chain/backtrace):

				record_mode:	call graph recording mode (fp|dwarf|lbr)
				record_size:	if record_mode is 'dwarf', max size of stack recording (<bytes>)
						default: 8192 (bytes)

				Default: fp

Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
---
 tools/perf/util/callchain.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/tools/perf/util/callchain.c b/tools/perf/util/callchain.c
index 1b60985..a8cf456 100644
--- a/tools/perf/util/callchain.c
+++ b/tools/perf/util/callchain.c
@@ -18,6 +18,7 @@
 #include <math.h>
 #include <linux/string.h>
 #include <linux/zalloc.h>
+#include <sys/utsname.h>
 
 #include "asm/bug.h"
 
@@ -278,6 +279,16 @@ int parse_callchain_record(const char *arg, struct callchain_param *param)
 		} else if (!strncmp(name, "dwarf", sizeof("dwarf"))) {
 			const unsigned long default_stack_dump_size = 8192;
 
+			if (system("grep -q 'CONFIG_DWARF=y' .config-detected") != 0) {
+				struct utsname uts;
+
+				ret = uname(&uts);
+				pr_err("DWARF is not supported for architecture %s\n",
+					ret ? "unknown" : uts.machine);
+
+				return -ENOTSUP;
+			}
+
 			ret = 0;
 			param->record_mode = CALLCHAIN_DWARF;
 			param->dump_size = default_stack_dump_size;
-- 
2.1.0