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

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

[Arnaldo Carvalho de Melo]

Em Wed, Sep 22, 2021 at 09:36:11AM -0700, Ian Rogers escreveu:
> 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.

We can adapt :-)

⬢[acme@toolbox perf]$ sed -n -e '/static bool is_ignored_symbol.*/,/^}.*/ p' scripts/kallsyms.c > original
⬢[acme@toolbox perf]$ sed -n -e '/static bool is_ignored_symbol.*/,/^}.*/ p' tools/perf/tests/vmlinux-kallsyms.c > copy
⬢[acme@toolbox perf]$ diff -u original copy
⬢[acme@toolbox perf]$

⬢[acme@toolbox perf]$ sed -n -e '/static bool is_ignored_symbol.*/,/^}.*/ p' scripts/kallsyms.c 
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 */
		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;
}
⬢[acme@toolbox perf]$

This should be added to tools/perf/check-headers.sh as a new
function_check() function that receives three parameters:

	function_check scripts/kallsyms.c tools/perf/tests/vmlinux-kallsyms.c is_ignored_symbol

The regexps can also be tightened up a bit.

Michael, can you cook up a patch for this?

Thanks,

- Arnaldo