linux-kernel - [PATCH] scripts/kallsyms: skip ppc compiler stub *.long_branch.* / *.plt

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Date:   Wed, 23 Sep 2020 02:48:56 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     linux-kbuild@...r.kernel.org
Cc:     Guenter Roeck <linux@...ck-us.net>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] scripts/kallsyms: skip ppc compiler stub *.long_branch.* / *.plt_branch.*

PowerPC allmodconfig often fails to build as follows:

    LD      .tmp_vmlinux.kallsyms1
    KSYM    .tmp_vmlinux.kallsyms1.o
    LD      .tmp_vmlinux.kallsyms2
    KSYM    .tmp_vmlinux.kallsyms2.o
    LD      .tmp_vmlinux.kallsyms3
    KSYM    .tmp_vmlinux.kallsyms3.o
    LD      vmlinux
    SORTTAB vmlinux
    SYSMAP  System.map
  Inconsistent kallsyms data
  Try make KALLSYMS_EXTRA_PASS=1 as a workaround
  make[2]: *** [../Makefile:1162: vmlinux] Error 1

Setting KALLSYMS_EXTRA_PASS=1 does not help.

This is caused by the compiler inserting stubs such as *.long_branch.*
and *.plt_branch.*

  $ powerpc-linux-nm -n .tmp_vmlinux.kallsyms2
   [ snip ]
  c00000000210c000 T __init_begin
  c00000000210c000 T _sinittext
  c00000000210c010 t 00000075.plt_branch.da9:19
  c00000000210c020 t 00000075.plt_branch.1677:5
  c00000000210c030 t 00000075.long_branch.memmove
  c00000000210c034 t 00000075.plt_branch.9e0:5
  c00000000210c044 t 00000075.plt_branch.free_initrd_mem
    ...

Actually, the problem mentioned in scripts/link-vmlinux.sh comments;
"In theory it's possible this results in even more stubs, but unlikely"
is happening here, and ends up with another kallsyms step required.

scripts/kallsyms.c already ignores various compiler stubs. Let's do
similar to make kallsysms for PowerPC always succeed in 2 steps.

Reported-by: Guenter Roeck <linux@...ck-us.net>
Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
---

 scripts/kallsyms.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
index 0096cd965332..306b9b38150f 100644
--- a/scripts/kallsyms.c
+++ b/scripts/kallsyms.c
@@ -120,17 +120,25 @@ static bool is_ignored_symbol(const char *name, char type)
 		NULL
 	};
 
+	static const char * const ignored_matches[] = {
+		".long_branch.",	/* ppc stub */
+		".plt_branch.",		/* ppc stub */
+		NULL
+	};
+
 	const char * const *p;
 
-	/* Exclude symbols which vary between passes. */
+	/* ignore symbol names that exactly match to a particular string. */
 	for (p = ignored_symbols; *p; p++)
 		if (!strcmp(name, *p))
 			return true;
 
+	/* ignore symbol names that start with a particular string. */
 	for (p = ignored_prefixes; *p; p++)
 		if (!strncmp(name, *p, strlen(*p)))
 			return true;
 
+	/* ignore symbol names that end with a particular string. */
 	for (p = ignored_suffixes; *p; p++) {
 		int l = strlen(name) - strlen(*p);
 
@@ -138,6 +146,12 @@ static bool is_ignored_symbol(const char *name, char type)
 			return true;
 	}
 
+	/* ignore symbol names that contain a particular string. */
+	for (p = ignored_matches; *p; p++) {
+		if (strstr(name, *p))
+			return true;
+	}
+
 	if (type == 'U' || type == 'u')
 		return true;
 	/* exclude debugging symbols */
-- 
2.25.1