linux-kernel - [PATCH] scripts/kallsyms: Ignore symbol type 'n'

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Date:   Wed,  4 Oct 2017 09:54:23 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        linux-kernel@...r.kernel.org, Guenter Roeck <linux@...ck-us.net>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: [PATCH] scripts/kallsyms: Ignore symbol type 'n'

gcc on aarch64 may emit synbols of type 'n' if the kernel is built with
'-frecord-gcc-switches'. In most cases, those symbols are reported
with nm as
	000000000000000e n $d
and with objdump as
	0000000000000000 l    d  .GCC.command.line	0000000000000000 .GCC.command.line
	000000000000000e l       .GCC.command.line	0000000000000000 $d

Those symbols are detected in is_arm_mapping_symbol() and ignored. However,
if "--prefix-symbols=<prefix>" is configured as well, the situation is
different. For example, in efi/libstub, arm64 images are built with
	'--prefix-alloc-sections=.init --prefix-symbols=__efistub_'.
In combination with '-frecord-gcc-switches', the symbols are now reported
by nm as:
	000000000000000e n __efistub_$d
and by objdump as:
	0000000000000000 l    d  .GCC.command.line	0000000000000000 .GCC.command.line
	000000000000000e l       .GCC.command.line	0000000000000000 __efistub_$d

Those symbols are no longer ignored and included in the base address
calculation. This results in a base address of 000000000000000e, which
in turn causes kallsyms to abort with
    kallsyms failure:
	relative symbol value 0xffffff900800a000 out of range in relative mode

The problem is seen in little endian arm64 builds with CONFIG_EFI enabled
and with '-frecord-gcc-switches' set in KCFLAGS.

Explicitly ignore symbols of type 'n' since those are clearly debug
symbols.

Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Signed-off-by: Guenter Roeck <linux@...ck-us.net>
---
 scripts/kallsyms.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
index 5d554419170b..9ee9bf7fd1a2 100644
--- a/scripts/kallsyms.c
+++ b/scripts/kallsyms.c
@@ -158,7 +158,7 @@ static int read_symbol(FILE *in, struct sym_entry *s)
 	else if (str[0] == '$')
 		return -1;
 	/* exclude debugging symbols */
-	else if (stype == 'N')
+	else if (stype == 'N' || stype == 'n')
 		return -1;
 
 	/* include the type field in the symbol name, so that it gets
-- 
2.7.4