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* [PATCH] perf symbols: Remove demangle-rust files as superfluous
@ 2022-02-01 18:50 German Gomez
  2022-02-02  0:12 ` Arnaldo Carvalho de Melo
  2022-02-09 18:41 ` Miguel Ojeda
  0 siblings, 2 replies; 6+ messages in thread
From: German Gomez @ 2022-02-01 18:50 UTC (permalink / raw)
  To: linux-kernel, linux-perf-users, acme
  Cc: German Gomez, Mark Rutland, Alexander Shishkin, Jiri Olsa,
	Namhyung Kim

Demangling of Rust legacy symbols has been working through libbfd for
some time now, making these files no longer needed, so remove them.

Signed-off-by: German Gomez <german.gomez@arm.com>
---
Before and after the commit:

$ perf record rustc
$ perf report

2.98%  rustc    rustc                                [.] <std::collections::hash::map::DefaultHasher as core::hash::Hasher>::write
2.77%  rustc    rustc                                [.] std::collections::hash::map::HashMap<K,V,S>::entry
2.09%  rustc    rustc                                [.] <<toml::value::Value as serde::de::Deserialize>::deserialize::ValueVisitor as serde::de::Visitor>::visit_map
2.05%  rustc    rustc                                [.] <toml::de::MapVisitor as serde::de::MapAccess>::next_key_seed
1.52%  rustc    rustc                                [.] std::collections::hash::map::HashMap<K,V,S>::get
0.59%  rustc    rustc                                [.] <toml::de::MapVisitor as serde::de::MapAccess>::next_value_seed
---
 tools/perf/util/Build           |   1 -
 tools/perf/util/demangle-rust.c | 269 --------------------------------
 tools/perf/util/demangle-rust.h |   8 -
 tools/perf/util/symbol-elf.c    |   7 -
 4 files changed, 285 deletions(-)
 delete mode 100644 tools/perf/util/demangle-rust.c
 delete mode 100644 tools/perf/util/demangle-rust.h

diff --git a/tools/perf/util/Build b/tools/perf/util/Build
index 2a403cefc..e59788ef6 100644
--- a/tools/perf/util/Build
+++ b/tools/perf/util/Build
@@ -193,7 +193,6 @@ perf-$(CONFIG_LIBCAP) += cap.o
 
 perf-y += demangle-ocaml.o
 perf-y += demangle-java.o
-perf-y += demangle-rust.o
 
 ifdef CONFIG_JITDUMP
 perf-$(CONFIG_LIBELF) += jitdump.o
diff --git a/tools/perf/util/demangle-rust.c b/tools/perf/util/demangle-rust.c
deleted file mode 100644
index a659fc69f..000000000
--- a/tools/perf/util/demangle-rust.c
+++ /dev/null
@@ -1,269 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0
-#include <string.h>
-#include "debug.h"
-
-#include "demangle-rust.h"
-
-/*
- * Mangled Rust symbols look like this:
- *
- *     _$LT$std..sys..fd..FileDesc$u20$as$u20$core..ops..Drop$GT$::drop::hc68340e1baa4987a
- *
- * The original symbol is:
- *
- *     <std::sys::fd::FileDesc as core::ops::Drop>::drop
- *
- * The last component of the path is a 64-bit hash in lowercase hex, prefixed
- * with "h". Rust does not have a global namespace between crates, an illusion
- * which Rust maintains by using the hash to distinguish things that would
- * otherwise have the same symbol.
- *
- * Any path component not starting with a XID_Start character is prefixed with
- * "_".
- *
- * The following escape sequences are used:
- *
- *     ","  =>  $C$
- *     "@"  =>  $SP$
- *     "*"  =>  $BP$
- *     "&"  =>  $RF$
- *     "<"  =>  $LT$
- *     ">"  =>  $GT$
- *     "("  =>  $LP$
- *     ")"  =>  $RP$
- *     " "  =>  $u20$
- *     "'"  =>  $u27$
- *     "["  =>  $u5b$
- *     "]"  =>  $u5d$
- *     "~"  =>  $u7e$
- *
- * A double ".." means "::" and a single "." means "-".
- *
- * The only characters allowed in the mangled symbol are a-zA-Z0-9 and _.:$
- */
-
-static const char *hash_prefix = "::h";
-static const size_t hash_prefix_len = 3;
-static const size_t hash_len = 16;
-
-static bool is_prefixed_hash(const char *start);
-static bool looks_like_rust(const char *sym, size_t len);
-static bool unescape(const char **in, char **out, const char *seq, char value);
-
-/*
- * INPUT:
- *     sym: symbol that has been through BFD-demangling
- *
- * This function looks for the following indicators:
- *
- *  1. The hash must consist of "h" followed by 16 lowercase hex digits.
- *
- *  2. As a sanity check, the hash must use between 5 and 15 of the 16 possible
- *     hex digits. This is true of 99.9998% of hashes so once in your life you
- *     may see a false negative. The point is to notice path components that
- *     could be Rust hashes but are probably not, like "haaaaaaaaaaaaaaaa". In
- *     this case a false positive (non-Rust symbol has an important path
- *     component removed because it looks like a Rust hash) is worse than a
- *     false negative (the rare Rust symbol is not demangled) so this sets the
- *     balance in favor of false negatives.
- *
- *  3. There must be no characters other than a-zA-Z0-9 and _.:$
- *
- *  4. There must be no unrecognized $-sign sequences.
- *
- *  5. There must be no sequence of three or more dots in a row ("...").
- */
-bool
-rust_is_mangled(const char *sym)
-{
-	size_t len, len_without_hash;
-
-	if (!sym)
-		return false;
-
-	len = strlen(sym);
-	if (len <= hash_prefix_len + hash_len)
-		/* Not long enough to contain "::h" + hash + something else */
-		return false;
-
-	len_without_hash = len - (hash_prefix_len + hash_len);
-	if (!is_prefixed_hash(sym + len_without_hash))
-		return false;
-
-	return looks_like_rust(sym, len_without_hash);
-}
-
-/*
- * A hash is the prefix "::h" followed by 16 lowercase hex digits. The hex
- * digits must comprise between 5 and 15 (inclusive) distinct digits.
- */
-static bool is_prefixed_hash(const char *str)
-{
-	const char *end;
-	bool seen[16];
-	size_t i;
-	int count;
-
-	if (strncmp(str, hash_prefix, hash_prefix_len))
-		return false;
-	str += hash_prefix_len;
-
-	memset(seen, false, sizeof(seen));
-	for (end = str + hash_len; str < end; str++)
-		if (*str >= '0' && *str <= '9')
-			seen[*str - '0'] = true;
-		else if (*str >= 'a' && *str <= 'f')
-			seen[*str - 'a' + 10] = true;
-		else
-			return false;
-
-	/* Count how many distinct digits seen */
-	count = 0;
-	for (i = 0; i < 16; i++)
-		if (seen[i])
-			count++;
-
-	return count >= 5 && count <= 15;
-}
-
-static bool looks_like_rust(const char *str, size_t len)
-{
-	const char *end = str + len;
-
-	while (str < end)
-		switch (*str) {
-		case '$':
-			if (!strncmp(str, "$C$", 3))
-				str += 3;
-			else if (!strncmp(str, "$SP$", 4)
-					|| !strncmp(str, "$BP$", 4)
-					|| !strncmp(str, "$RF$", 4)
-					|| !strncmp(str, "$LT$", 4)
-					|| !strncmp(str, "$GT$", 4)
-					|| !strncmp(str, "$LP$", 4)
-					|| !strncmp(str, "$RP$", 4))
-				str += 4;
-			else if (!strncmp(str, "$u20$", 5)
-					|| !strncmp(str, "$u27$", 5)
-					|| !strncmp(str, "$u5b$", 5)
-					|| !strncmp(str, "$u5d$", 5)
-					|| !strncmp(str, "$u7e$", 5))
-				str += 5;
-			else
-				return false;
-			break;
-		case '.':
-			/* Do not allow three or more consecutive dots */
-			if (!strncmp(str, "...", 3))
-				return false;
-			/* Fall through */
-		case 'a' ... 'z':
-		case 'A' ... 'Z':
-		case '0' ... '9':
-		case '_':
-		case ':':
-			str++;
-			break;
-		default:
-			return false;
-		}
-
-	return true;
-}
-
-/*
- * INPUT:
- *     sym: symbol for which rust_is_mangled(sym) returns true
- *
- * The input is demangled in-place because the mangled name is always longer
- * than the demangled one.
- */
-void
-rust_demangle_sym(char *sym)
-{
-	const char *in;
-	char *out;
-	const char *end;
-
-	if (!sym)
-		return;
-
-	in = sym;
-	out = sym;
-	end = sym + strlen(sym) - (hash_prefix_len + hash_len);
-
-	while (in < end)
-		switch (*in) {
-		case '$':
-			if (!(unescape(&in, &out, "$C$", ',')
-					|| unescape(&in, &out, "$SP$", '@')
-					|| unescape(&in, &out, "$BP$", '*')
-					|| unescape(&in, &out, "$RF$", '&')
-					|| unescape(&in, &out, "$LT$", '<')
-					|| unescape(&in, &out, "$GT$", '>')
-					|| unescape(&in, &out, "$LP$", '(')
-					|| unescape(&in, &out, "$RP$", ')')
-					|| unescape(&in, &out, "$u20$", ' ')
-					|| unescape(&in, &out, "$u27$", '\'')
-					|| unescape(&in, &out, "$u5b$", '[')
-					|| unescape(&in, &out, "$u5d$", ']')
-					|| unescape(&in, &out, "$u7e$", '~'))) {
-				pr_err("demangle-rust: unexpected escape sequence");
-				goto done;
-			}
-			break;
-		case '_':
-			/*
-			 * If this is the start of a path component and the next
-			 * character is an escape sequence, ignore the
-			 * underscore. The mangler inserts an underscore to make
-			 * sure the path component begins with a XID_Start
-			 * character.
-			 */
-			if ((in == sym || in[-1] == ':') && in[1] == '$')
-				in++;
-			else
-				*out++ = *in++;
-			break;
-		case '.':
-			if (in[1] == '.') {
-				/* ".." becomes "::" */
-				*out++ = ':';
-				*out++ = ':';
-				in += 2;
-			} else {
-				/* "." becomes "-" */
-				*out++ = '-';
-				in++;
-			}
-			break;
-		case 'a' ... 'z':
-		case 'A' ... 'Z':
-		case '0' ... '9':
-		case ':':
-			*out++ = *in++;
-			break;
-		default:
-			pr_err("demangle-rust: unexpected character '%c' in symbol\n",
-				*in);
-			goto done;
-		}
-
-done:
-	*out = '\0';
-}
-
-static bool unescape(const char **in, char **out, const char *seq, char value)
-{
-	size_t len = strlen(seq);
-
-	if (strncmp(*in, seq, len))
-		return false;
-
-	**out = value;
-
-	*in += len;
-	*out += 1;
-
-	return true;
-}
diff --git a/tools/perf/util/demangle-rust.h b/tools/perf/util/demangle-rust.h
deleted file mode 100644
index 2fca618b1..000000000
--- a/tools/perf/util/demangle-rust.h
+++ /dev/null
@@ -1,8 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0 */
-#ifndef __PERF_DEMANGLE_RUST
-#define __PERF_DEMANGLE_RUST 1
-
-bool rust_is_mangled(const char *str);
-void rust_demangle_sym(char *str);
-
-#endif /* __PERF_DEMANGLE_RUST */
diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index 31cd59a2b..3ed0bef81 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -14,7 +14,6 @@
 #include "symsrc.h"
 #include "demangle-ocaml.h"
 #include "demangle-java.h"
-#include "demangle-rust.h"
 #include "machine.h"
 #include "vdso.h"
 #include "debug.h"
@@ -258,12 +257,6 @@ static char *demangle_sym(struct dso *dso, int kmodule, const char *elf_name)
 			demangled = java_demangle_sym(elf_name, JAVA_DEMANGLE_NORET);
 		}
 	}
-	else if (rust_is_mangled(demangled))
-		/*
-		    * Input to Rust demangling is the BFD-demangled
-		    * name which it Rust-demangles in place.
-		    */
-		rust_demangle_sym(demangled);
 
 	return demangled;
 }
-- 
2.25.1


^ permalink raw reply related	[flat|nested] 6+ messages in thread
end of thread, other threads:[~2022-02-09 21:08 UTC | newest]

Thread overview: 6+ messages (download: mbox.gz follow: Atom feed
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2022-02-01 18:50 [PATCH] perf symbols: Remove demangle-rust files as superfluous German Gomez
2022-02-02  0:12 ` Arnaldo Carvalho de Melo
2022-02-02 14:55   ` German Gomez
2022-02-09 18:41 ` Miguel Ojeda
2022-02-09 20:54   ` German Gomez
2022-02-09 21:08     ` Miguel Ojeda

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