linux-kernel - Re: [PATCH v4 3/3] UBSAN: run-time undefined behavior sanity checker

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Message-Id: <20151208155914.d0b005c82906f3203660fd47@linux-foundation.org>
Date:	Tue, 8 Dec 2015 15:59:14 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Andrey Ryabinin <aryabinin@...tuozzo.com>
Cc:	<linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Sasha Levin <sasha.levin@...cle.com>,
	Randy Dunlap <rdunlap@...radead.org>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Jonathan Corbet <corbet@....net>,
	Michal Marek <mmarek@...e.cz>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Yury Gribov <y.gribov@...sung.com>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Konstantin Khlebnikov <koct9i@...il.com>,
	Kostya Serebryany <kcc@...gle.com>, <x86@...nel.org>,
	<linux-doc@...r.kernel.org>, <linux-kbuild@...r.kernel.org>
Subject: Re: [PATCH v4 3/3] UBSAN: run-time undefined behavior sanity
 checker

On Thu, 3 Dec 2015 18:50:07 +0300 Andrey Ryabinin <aryabinin@...tuozzo.com> wrote:

> UBSAN uses compile-time instrumentation to catch undefined behavior (UB).
> Compiler inserts code that perform certain kinds of checks before
> operations that could cause UB. If check fails (i.e. UB detected)
> __ubsan_handle_* function called to print error message.
> 
> So the most of the work is done by compiler. This patch just
> implements ubsan handlers printing errors.
> 
> GCC has this capability since 4.9.x [1] (see -fsanitize=undefined
> option and its suboptions).
> However GCC 5.x has more checkers implemented [2].
> Article [3] has a bit more details about UBSAN in the GCC.
> 
> ...
>
> +#ifdef CONFIG_ARCH_SUPPORTS_INT128
> +typedef __int128 s_max;
> +typedef unsigned __int128 u_max;
> +#else

In file included from lib/ubsan.c:21:
lib/ubsan.h:77: error: expected '=', ',', ';', 'asm' or '__attribute__' before 's_max'
lib/ubsan.h:78: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'u_max'
lib/ubsan.c:89: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'get_signed_val'


gcc-4.4.4 doesn't appear to like __int128.  The only other use of
__int128 is include/linux/math64.h:mul_u64_u32_shr() and it uses
defined(__SIZEOF_INT128__) as well.

Using that gives me

lib/ubsan.c: In function 'val_to_string':
lib/ubsan.c:127: warning: right shift count >= width of type
lib/ubsan.c:128: warning: right shift count >= width of type

so I bodged that site too.  I need to get an mmotm release out the door.


--- a/lib/ubsan.c~ubsan-run-time-undefined-behavior-sanity-checker-fix-3
+++ a/lib/ubsan.c
@@ -120,7 +120,7 @@ static void val_to_string(char *str, siz
 {
 	if (type_is_int(type)) {
 		if (type_bit_width(type) == 128) {
-#ifdef CONFIG_ARCH_SUPPORTS_INT128
+#if defined(CONFIG_ARCH_SUPPORTS_INT128) && defined(__SIZEOF_INT128__)
 			u_max val = get_unsigned_val(type, value);
 
 			scnprintf(str, size, "0x%08x%08x%08x%08x",
--- a/lib/ubsan.h~ubsan-run-time-undefined-behavior-sanity-checker-fix-3
+++ a/lib/ubsan.h
@@ -73,7 +73,7 @@ struct invalid_value_data {
 	struct type_descriptor *type;
 };
 
-#ifdef CONFIG_ARCH_SUPPORTS_INT128
+#if defined(CONFIG_ARCH_SUPPORTS_INT128) && defined(__SIZEOF_INT128__)
 typedef __int128 s_max;
 typedef unsigned __int128 u_max;
 #else
_

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