perf annotate: Adapt arch__dwarf_regnum() for arm64

Currently, arch__dwarf_regnum() assumes that all architectures use a
register prefix character (e.g., '%' for x86) defined by
arch->objdump.register_char, and uses it to match register names in
objdump output. However, this assumption does not hold for arm64,
where assembly syntax uses bare register names like 'x0', 'w1'
without any prefix.

As a result, arm64 builds may fail to correctly recognize register
names from objdump disassembly, leading to incomplete or incorrect
annotation output.

To address this:

- Make the register prefix check optional, allowing architectures
  without a prefix character to be parsed correctly.

- Extend the delimiter set in strpbrk() to include the closing square
  bracket ']'. In arm64 assembly, memory operands often use bracketed
  syntax such as '[x1, #16]' or '[x2]'. Adding ']' ensures clean
  extraction of register names like 'x2' without trailing characters.

Reviewed-by: Ian Rogers <irogers@google.com>
Reviewed-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Tengda Wu <wutengda@huaweicloud.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 7 insertions, 5 deletions

diff --git a/tools/perf/util/annotate.c b/tools/perf/util/annotate.c
index d3482eba9283..86a4beec6528 100644
--- a/tools/perf/util/annotate.c
+++ b/tools/perf/util/annotate.c
@@ -2582,19 +2582,21 @@ int annotate_check_args(void)
 
 int arch__dwarf_regnum(const struct arch *arch, const char *str)
 {
-	const char *p;
+	const char *p = str;
 	char *regname, *q;
 	int reg;
 
-	p = strchr(str, arch->objdump.register_char);
-	if (p == NULL)
-		return -1;
+	if (arch->objdump.register_char) {
+		p = strchr(str, arch->objdump.register_char);
+		if (p == NULL)
+			return -1;
+	}
 
 	regname = strdup(p);
 	if (regname == NULL)
 		return -1;
 
-	q = strpbrk(regname, ",) ");
+	q = strpbrk(regname, ",)] ");
 	if (q)
 		*q = '\0';