Re: [PATCH] perf tests vmlinux-kallsyms: ignore hidden symbols

[Ian Rogers <irogers@google.com>]

On Wed, Sep 22, 2021 at 8:27 AM Michael Petlan <mpetlan@redhat.com> wrote:
>
> Certain kernel symbols are purposely hidden from kallsyms. The function
> is_ignored_symbol() from scripts/kallsyms.c decides if a symbol should
> be hidden or not.
>
> The perf test "vmlinux symtab matches kallsyms" fails in case perf finds
> some of the hidden symbols in its machine image and can't match them to
> kallsyms.
>
> Let's add a filter to check if a symbol not found isn't one of these
> before failing the test.
>
> The function is_ignored_symbol() has been copied from scripts/kallsyms.c
> and needs to be updated along with the original.
>
> Signed-off-by: Michael Petlan <mpetlan@redhat.com>

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

It is a shame this can't be a library to ensure the function is kept in sync.

> ---
>  tools/perf/tests/vmlinux-kallsyms.c | 102 ++++++++++++++++++++++++++++
>  1 file changed, 102 insertions(+)
>
> diff --git a/tools/perf/tests/vmlinux-kallsyms.c b/tools/perf/tests/vmlinux-kallsyms.c
> index 193b7c91b4e2..4f884aabc7f4 100644
> --- a/tools/perf/tests/vmlinux-kallsyms.c
> +++ b/tools/perf/tests/vmlinux-kallsyms.c
> @@ -3,6 +3,7 @@
>  #include <linux/rbtree.h>
>  #include <inttypes.h>
>  #include <string.h>
> +#include <ctype.h>
>  #include <stdlib.h>
>  #include "dso.h"
>  #include "map.h"
> @@ -14,6 +15,102 @@
>
>  #define UM(x) kallsyms_map->unmap_ip(kallsyms_map, (x))
>
> +static bool is_ignored_symbol(const char *name, char type)
> +{
> +       /* Symbol names that exactly match to the following are ignored.*/
> +       static const char * const ignored_symbols[] = {
> +               /*
> +                * Symbols which vary between passes. Passes 1 and 2 must have
> +                * identical symbol lists. The kallsyms_* symbols below are
> +                * only added after pass 1, they would be included in pass 2
> +                * when --all-symbols is specified so exclude them to get a
> +                * stable symbol list.
> +                */
> +               "kallsyms_addresses",
> +               "kallsyms_offsets",
> +               "kallsyms_relative_base",
> +               "kallsyms_num_syms",
> +               "kallsyms_names",
> +               "kallsyms_markers",
> +               "kallsyms_token_table",
> +               "kallsyms_token_index",
> +               /* Exclude linker generated symbols which vary between passes */
> +               "_SDA_BASE_",           /* ppc */
> +               "_SDA2_BASE_",          /* ppc */

Do values like this belong behind an architecture #ifdef? I know
that's not currently the case in scripts/kallsyms.c.

> +               NULL
> +       };
> +
> +       /* Symbol names that begin with the following are ignored.*/
> +       static const char * const ignored_prefixes[] = {
> +               "$",                    /* local symbols for ARM, MIPS, etc. */
> +               ".LASANPC",             /* s390 kasan local symbols */
> +               "__crc_",               /* modversions */
> +               "__efistub_",           /* arm64 EFI stub namespace */
> +               "__kvm_nvhe_",          /* arm64 non-VHE KVM namespace */
> +               "__AArch64ADRPThunk_",  /* arm64 lld */
> +               "__ARMV5PILongThunk_",  /* arm lld */
> +               "__ARMV7PILongThunk_",
> +               "__ThumbV7PILongThunk_",
> +               "__LA25Thunk_",         /* mips lld */
> +               "__microLA25Thunk_",
> +               NULL
> +       };
> +
> +       /* Symbol names that end with the following are ignored.*/
> +       static const char * const ignored_suffixes[] = {
> +               "_from_arm",            /* arm */
> +               "_from_thumb",          /* arm */
> +               "_veneer",              /* arm */
> +               NULL
> +       };
> +
> +       /* Symbol names that contain the following are ignored.*/
> +       static const char * const ignored_matches[] = {
> +               ".long_branch.",        /* ppc stub */
> +               ".plt_branch.",         /* ppc stub */
> +               NULL
> +       };
> +
> +       const char * const *p;
> +
> +       for (p = ignored_symbols; *p; p++)
> +               if (!strcmp(name, *p))
> +                       return true;
> +
> +       for (p = ignored_prefixes; *p; p++)
> +               if (!strncmp(name, *p, strlen(*p)))
> +                       return true;
> +
> +       for (p = ignored_suffixes; *p; p++) {
> +               int l = strlen(name) - strlen(*p);
> +
> +               if (l >= 0 && !strcmp(name + l, *p))
> +                       return true;
> +       }
> +
> +       for (p = ignored_matches; *p; p++) {
> +               if (strstr(name, *p))
> +                       return true;
> +       }
> +
> +       if (type == 'U' || type == 'u')
> +               return true;
> +       /* exclude debugging symbols */
> +       if (type == 'N' || type == 'n')
> +               return true;
> +
> +       if (toupper(type) == 'A') {
> +               /* Keep these useful absolute symbols */
> +               if (strcmp(name, "__kernel_syscall_via_break") &&
> +                   strcmp(name, "__kernel_syscall_via_epc") &&
> +                   strcmp(name, "__kernel_sigtramp") &&
> +                   strcmp(name, "__gp"))
> +                       return true;
> +       }
> +
> +       return false;
> +}
> +
>  int test__vmlinux_matches_kallsyms(struct test *test __maybe_unused, int subtest __maybe_unused)
>  {
>         int err = -1;
> @@ -169,6 +266,11 @@ int test__vmlinux_matches_kallsyms(struct test *test __maybe_unused, int subtest
>                          * such as __indirect_thunk_end.
>                          */
>                         continue;
> +               } else if (is_ignored_symbol(sym->name, sym->type)) {
> +                       /*
> +                        * Ignore hidden symbols, see scripts/kallsyms.c for the details
> +                        */
> +                       continue;
>                 } else {
>                         pr_debug("ERR : %#" PRIx64 ": %s not on kallsyms\n",
>                                  mem_start, sym->name);
> --
> 2.18.4
>