Re: [PATCH 3/3] perf jvmti: Fix demangling Java symbols

[Ian Rogers <irogers@google.com>]

On Sun, Apr 26, 2020 at 11:16 PM Nick Gasson <nick.gasson@arm.com> wrote:
>
> For a Java method signature like:
>
>     Ljava/lang/AbstractStringBuilder;appendChars(Ljava/lang/String;II)V
>
> The demangler produces:
>
>     void class java.lang.AbstractStringBuilder.appendChars(class java.lang., shorttring., int, int)
>
> The arguments should be (java.lang.String, int, int) but the demangler
> interprets the "S" in String as the type code for "short". Correct this
> and two other minor things:
>
> - There is no "bool" type in Java, should be "boolean".
>
> - The demangler prepends "class" to every Java class name. This is not
>   standard Java syntax and it wastes a lot of horizontal space if the
>   signature is long. Remove this as there isn't any ambiguity between
>   class names and primitives.
>
> Also added a test case.
>
> Signed-off-by: Nick Gasson <nick.gasson@arm.com>

Reviewed-by: Ian Rogers <irogers@google.com>
Tested-by: Ian Rogers <irogers@google.com>

Thanks!
Ian

> ---
>  tools/perf/tests/Build                |  1 +
>  tools/perf/tests/builtin-test.c       |  4 +++
>  tools/perf/tests/demangle-java-test.c | 42 +++++++++++++++++++++++++++
>  tools/perf/tests/tests.h              |  1 +
>  tools/perf/util/demangle-java.c       | 13 +++++----
>  5 files changed, 55 insertions(+), 6 deletions(-)
>  create mode 100644 tools/perf/tests/demangle-java-test.c
>
> diff --git a/tools/perf/tests/Build b/tools/perf/tests/Build
> index 1692529639b0..2c45ac4a9581 100644
> --- a/tools/perf/tests/Build
> +++ b/tools/perf/tests/Build
> @@ -55,6 +55,7 @@ perf-y += mem2node.o
>  perf-y += maps.o
>  perf-y += time-utils-test.o
>  perf-y += genelf.o
> +perf-y += demangle-java-test.o
>
>  $(OUTPUT)tests/llvm-src-base.c: tests/bpf-script-example.c tests/Build
>         $(call rule_mkdir)
> diff --git a/tools/perf/tests/builtin-test.c b/tools/perf/tests/builtin-test.c
> index 54d9516c9839..03b362b37f97 100644
> --- a/tools/perf/tests/builtin-test.c
> +++ b/tools/perf/tests/builtin-test.c
> @@ -309,6 +309,10 @@ static struct test generic_tests[] = {
>                 .desc = "maps__merge_in",
>                 .func = test__maps__merge_in,
>         },
> +       {
> +               .desc = "Demangle Java",
> +               .func = test__demangle_java,
> +       },
>         {
>                 .func = NULL,
>         },
> diff --git a/tools/perf/tests/demangle-java-test.c b/tools/perf/tests/demangle-java-test.c
> new file mode 100644
> index 000000000000..8f3b90832fb0
> --- /dev/null
> +++ b/tools/perf/tests/demangle-java-test.c
> @@ -0,0 +1,42 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include <string.h>
> +#include <stdlib.h>
> +#include <stdio.h>
> +#include "tests.h"
> +#include "session.h"
> +#include "debug.h"
> +#include "demangle-java.h"
> +
> +int test__demangle_java(struct test *test __maybe_unused, int subtest __maybe_unused)
> +{
> +       int ret = TEST_OK;
> +       char *buf = NULL;
> +       size_t i;
> +
> +       struct {
> +               const char *mangled, *demangled;
> +       } test_cases[] = {
> +               { "Ljava/lang/StringLatin1;equals([B[B)Z",
> +                 "boolean java.lang.StringLatin1.equals(byte[], byte[])" },
> +               { "Ljava/util/zip/ZipUtils;CENSIZ([BI)J",
> +                 "long java.util.zip.ZipUtils.CENSIZ(byte[], int)" },
> +               { "Ljava/util/regex/Pattern$BmpCharProperty;match(Ljava/util/regex/Matcher;ILjava/lang/CharSequence;)Z",
> +                 "boolean java.util.regex.Pattern$BmpCharProperty.match(java.util.regex.Matcher, int, java.lang.CharSequence)" },
> +               { "Ljava/lang/AbstractStringBuilder;appendChars(Ljava/lang/String;II)V",
> +                 "void java.lang.AbstractStringBuilder.appendChars(java.lang.String, int, int)" },
> +               { "Ljava/lang/Object;<init>()V",
> +                 "void java.lang.Object<init>()" },
> +       };
> +
> +       for (i = 0; i < sizeof(test_cases) / sizeof(test_cases[0]); i++) {
> +               buf = java_demangle_sym(test_cases[i].mangled, 0);
> +               if (strcmp(buf, test_cases[i].demangled)) {
> +                       pr_debug("FAILED: %s: %s != %s\n", test_cases[i].mangled,
> +                                buf, test_cases[i].demangled);
> +                       ret = TEST_FAIL;
> +               }
> +               free(buf);
> +       }
> +
> +       return ret;
> +}
> diff --git a/tools/perf/tests/tests.h b/tools/perf/tests/tests.h
> index 9a160fef47c9..49b791d978f6 100644
> --- a/tools/perf/tests/tests.h
> +++ b/tools/perf/tests/tests.h
> @@ -111,6 +111,7 @@ int test__mem2node(struct test *t, int subtest);
>  int test__maps__merge_in(struct test *t, int subtest);
>  int test__time_utils(struct test *t, int subtest);
>  int test__jit_write_elf(struct test *test, int subtest);
> +int test__demangle_java(struct test *test, int subtest);
>
>  bool test__bp_signal_is_supported(void);
>  bool test__bp_account_is_supported(void);
> diff --git a/tools/perf/util/demangle-java.c b/tools/perf/util/demangle-java.c
> index 6fb7f34c0814..39c05200ed65 100644
> --- a/tools/perf/util/demangle-java.c
> +++ b/tools/perf/util/demangle-java.c
> @@ -15,7 +15,7 @@ enum {
>         MODE_CLASS  = 1,
>         MODE_FUNC   = 2,
>         MODE_TYPE   = 3,
> -       MODE_CTYPE  = 3, /* class arg */
> +       MODE_CTYPE  = 4, /* class arg */
>  };
>
>  #define BASE_ENT(c, n) [c - 'A']=n
> @@ -27,7 +27,7 @@ static const char *base_types['Z' - 'A' + 1] = {
>         BASE_ENT('I', "int" ),
>         BASE_ENT('J', "long" ),
>         BASE_ENT('S', "short" ),
> -       BASE_ENT('Z', "bool" ),
> +       BASE_ENT('Z', "boolean" ),
>  };
>
>  /*
> @@ -59,15 +59,16 @@ __demangle_java_sym(const char *str, const char *end, char *buf, int maxlen, int
>
>                 switch (*q) {
>                 case 'L':
> -                       if (mode == MODE_PREFIX || mode == MODE_CTYPE) {
> -                               if (mode == MODE_CTYPE) {
> +                       if (mode == MODE_PREFIX || mode == MODE_TYPE) {
> +                               if (mode == MODE_TYPE) {
>                                         if (narg)
>                                                 rlen += scnprintf(buf + rlen, maxlen - rlen, ", ");
>                                         narg++;
>                                 }
> -                               rlen += scnprintf(buf + rlen, maxlen - rlen, "class ");
>                                 if (mode == MODE_PREFIX)
>                                         mode = MODE_CLASS;
> +                               else
> +                                       mode = MODE_CTYPE;
>                         } else
>                                 buf[rlen++] = *q;
>                         break;
> @@ -120,7 +121,7 @@ __demangle_java_sym(const char *str, const char *end, char *buf, int maxlen, int
>                         if (mode != MODE_CLASS && mode != MODE_CTYPE)
>                                 goto error;
>                         /* safe because at least one other char to process */
> -                       if (isalpha(*(q + 1)))
> +                       if (isalpha(*(q + 1)) && mode == MODE_CLASS)
>                                 rlen += scnprintf(buf + rlen, maxlen - rlen, ".");
>                         if (mode == MODE_CLASS)
>                                 mode = MODE_FUNC;
> --
> 2.26.1
>