elf.h SHF_EXCLUDE signed int 31 bit shift triggers undefined behaviour.
Commit Message
On Wed, 2015-04-22 at 11:18 +0200, Florian Weimer wrote:
> On 04/22/2015 10:14 AM, Florian Weimer wrote:
> > On 04/21/2015 11:20 AM, Mark Wielaard wrote:
> >> -#define SHF_EXCLUDE (1 << 31) /* Section is excluded unless
> >> +#define SHF_EXCLUDE (1U << 31) /* Section is excluded unless
> >
> > I think the safer change is to use -0x80000000 as the value of the
> > constant, without making it unsigned. Otherwise my previous objections
> > apply.
>
> I thought some more about this, and have changed my opinion completely.
> Making the constant unsigned is less risky than making it negative
> because of potential sign extension issues. It's the lesser of two evils.
>
> The proposed patch is okay with me.
Thanks. I didn't see other objections. So if it is good to go in could
someone please push it for me? (I don't have glibc git push access.)
ChangeLog
* elf/elf.h (SHF_EXCLUDE): Use unsigned 1 for shift.
Comments
On 04/28/2015 10:22 AM, Mark Wielaard wrote:
> Thanks. I didn't see other objections. So if it is good to go in could
> someone please push it for me? (I don't have glibc git push access.)
>
> ChangeLog
>
> * elf/elf.h (SHF_EXCLUDE): Use unsigned 1 for shift.
>
Thanks, committed.
From 86771e8963653c306e53c07e1640914081afb30a Mon Sep 17 00:00:00 2001
From: Mark Wielaard <mjw@redhat.com>
Date: Tue, 24 Mar 2015 11:32:36 +0100
Subject: [PATCH] elf.h SHF_EXCLUDE signed int 31 bit shift triggers undefined
behaviour.
Any use of SHF_EXCLUDE in code that tries to check it against sh_flags
will trigger undefined behaviour because it is defined as a 31 bit shift
against an signed integer. Fix by explicitly using an unsigned int.
---
ChangeLog | 4 ++++
elf/elf.h | 2 +-
2 files changed, 5 insertions(+), 1 deletion(-)
@@ -371,7 +371,7 @@ typedef struct
#define SHF_MASKPROC 0xf0000000 /* Processor-specific */
#define SHF_ORDERED (1 << 30) /* Special ordering requirement
(Solaris). */
-#define SHF_EXCLUDE (1 << 31) /* Section is excluded unless
+#define SHF_EXCLUDE (1U << 31) /* Section is excluded unless
referenced or allocated (Solaris).*/
/* Section group handling. */
--
1.8.3.1