[PATCH 5/5] perf symbol: Move Rust demangling into its own function

[Michal Pluta <michalpl2003@gmail.com>]

dso__demangle_sym() is the only place that implements demangling logic
inline.  The other three are one call each to a helper.  Move the Rust
parsing and buffer growth into rust_demangle_sym(), with the same
signature as the other three.

A Rust name that fails to demangle now falls through to the other
demanglers, matching how the other demanglers chain into each other.
A v0 name can't be misread by any of them, since none accepts its "_R"
prefix.  A legacy name can only fail here on allocation failure or
hitting the output bound, neither of which is language-specific.

Assisted-by: LLM
Signed-off-by: Michal Pluta <michalpl2003@gmail.com>
---
 tools/perf/util/symbol.c | 61 +++++++++++++++++++++++-----------------
 1 file changed, 35 insertions(+), 26 deletions(-)

diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
index 858a14a91f79..89db9a670833 100644
--- a/tools/perf/util/symbol.c
+++ b/tools/perf/util/symbol.c
@@ -2740,47 +2740,56 @@ char *cxx_demangle_sym(const char *str __maybe_unused, bool params __maybe_unuse
 /* Buffer limit for a demangled Rust symbol name. */
 #define RUST_DEMANGLE_MAX_LEN (1024 * 1024)
 
-char *dso__demangle_sym(struct dso *dso, int kmodule, const char *elf_name)
+static char *rust_demangle_sym(const char *elf_name)
 {
 	struct demangle rust_demangle = {
 		.style = DemangleStyleUnknown,
 	};
 	char *demangled = NULL;
 	size_t buf_len;
 
+	rust_demangle_demangle(elf_name, &rust_demangle);
+	if (!rust_demangle_is_known(&rust_demangle))
+		return NULL;
+
+	if (rust_demangle.mangled_len == 0)
+		return NULL;
+
+	for (buf_len = min_t(size_t, roundup_pow_of_two(rust_demangle.mangled_len * 2),
+			     RUST_DEMANGLE_MAX_LEN);
+	     buf_len <= RUST_DEMANGLE_MAX_LEN;
+	     buf_len *= 2) {
+		char *tmp = realloc(demangled, buf_len);
+
+		if (!tmp)
+			break;
+		demangled = tmp;
+		if (rust_demangle_display_demangle(&rust_demangle, demangled, buf_len,
+						   /*alternate=*/true) == OverflowOk) {
+			tmp = realloc(demangled, strlen(demangled) + 1);
+			return tmp ?: demangled;
+		}
+	}
+	/* Failure to grow output buffer or buffer exceeded sensible bounds. */
+	free(demangled);
+	return NULL;
+}
+
+char *dso__demangle_sym(struct dso *dso, int kmodule, const char *elf_name)
+{
+	char *demangled = NULL;
+
 	/*
 	 * We need to figure out if the object was created from C++ sources
 	 * DWARF DW_compile_unit has this, but we don't always have access
 	 * to it...
 	 */
 	if (!want_demangle((dso && dso__kernel(dso)) || kmodule))
 		return demangled;
 
-	rust_demangle_demangle(elf_name, &rust_demangle);
-	if (rust_demangle_is_known(&rust_demangle)) {
-		/* A rust mangled name. */
-		if (rust_demangle.mangled_len == 0)
-			return demangled;
-
-		for (buf_len = min_t(size_t, roundup_pow_of_two(rust_demangle.mangled_len * 2),
-				     RUST_DEMANGLE_MAX_LEN);
-		     buf_len <= RUST_DEMANGLE_MAX_LEN;
-		     buf_len *= 2) {
-			char *tmp = realloc(demangled, buf_len);
-
-			if (!tmp)
-				break;
-			demangled = tmp;
-			if (rust_demangle_display_demangle(&rust_demangle, demangled, buf_len,
-							   /*alternate=*/true) == OverflowOk) {
-				tmp = realloc(demangled, strlen(demangled) + 1);
-				return tmp ?: demangled;
-			}
-		}
-		/* Failure to grow output buffer or buffer exceeded sensible bounds. */
-		free(demangled);
-		return NULL;
-	}
+	demangled = rust_demangle_sym(elf_name);
+	if (demangled)
+		return demangled;
 
 	demangled = cxx_demangle_sym(elf_name, verbose > 0, verbose > 0);
 	if (demangled)
-- 
2.43.0