perf regs: Fix abort for "-I" or "--user-regs" options

Fix an issue where the `perf` tool aborts unexpectedly when running the
following command:

```
perf record -e cycles -I -- true

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

    -I, --intr-regs[=<any register>]
    sample selected machine registers on interrupt, use '-I?' to list register names
```

The usage of the `-I` or `--user-regs` options without specifying any
registers should default to sampling all general-purpose registers.

However, this currently causes an abnormal termination.

The issue was introduced by commit 3d06db9bad ("perf regs: Refactor
 use of arch__sample_reg_masks() to perf_reg_name()").

This patch resolves the problem, ensuring that the `-I` or `--user-regs`
options work as intended without causing an abort.

Fixes: 3d06db9bad ("perf regs: Refactor use of arch__sample_reg_masks() to perf_reg_name()")
Reviewed-by: Ian Rogers <irogers@google.com>
Signed-off-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Alexandre Ghiti <alex@ghiti.fr>
Cc: Guo Ren <guoren@kernel.org>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@linaro.org>
Cc: John Garry <john.g.garry@oracle.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-csky@vger.kernel.org
Cc: linux-riscv@lists.infradead.org
Cc: Mike Leach <mike.leach@linaro.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Paul Walmsley <pjw@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Falcon <thomas.falcon@intel.com>
Cc: Will Deacon <will@kernel.org>
Cc: Xudong Hao <xudong.hao@intel.com>
Cc: Zide Chen <zide.chen@intel.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/parse-regs-options.c

@@ -66,12 +66,14 @@ __parse_regs(const struct option *opt, const char *str, int unset, bool intr)
 	if (*mode)
 		return -1;
 
-	/* str may be NULL in case no arg is passed to -I */
-	if (!str)
-		return -1;
-
 	mask = intr ? arch__intr_reg_mask() : arch__user_reg_mask();
 
+	/* str may be NULL in case no arg is passed to -I */
+	if (!str) {
+		*mode = mask;
+		return 0;
+	}
+
 	/* because str is read-only */
 	s = os = strdup(str);
 	if (!s)
@@ -104,9 +106,6 @@ __parse_regs(const struct option *opt, const char *str, int unset, bool intr)
 	}
 	ret = 0;
 
-	/* default to all possible regs */
-	if (*mode == 0)
-		*mode = mask;
 error:
 	free(os);
 	return ret;