On Sun, 2015-01-25 at 14:30 -0800, Josh Stone wrote:
On 01/25/2015 11:42 AM, Hanno Böck wrote:
> When compiling elfutils with undefined behaviour sanitizer
> (-fsanitize=undefined) a warning will be shown indicating an invalid
> shiftleft operation on the attached elf file:
>
> readelf.c:1133:28: runtime error: left shift of 1 by 31 places cannot
> be represented in type 'int'
>
> Tested with elfutils-0.161. This was found with zzuf.
Ah, this has nothing to do with your input -- "readelf -S readelf" also
triggers the same message.
That line is:
if (shdr->sh_flags & SHF_EXCLUDE)
That macro is:
#define SHF_EXCLUDE (1 << 31)
Now, shdr is GElf_Shdr*, a typedef of Elf64_Shdr, so sh_flags is
Elf64_Xword. Even the 32-bit case has Elf32_Word, which is unsigned so
it would be fine. But (1 << 31) will be evaluated as int *before* the
type promotion for "&". It should probably be (1U << 31) instead,
and
maybe use 1U for all flags to be consistent.
Nice find. So any use of SHF_EXCLUDE on an architecture that has 32bit
ints triggers undefined behavior. Your suggested fix was also used in a
similar case in commit 7c757b "readelf.c (print_gdb_index_section): Use
unsigned int for 31 bits left shift."
elf.h is actually part of glibc and we just import a new version when
needed. Would you mind suggesting the fix there
(libc-alpha(a)sourceware.org) and when accepted we'll import the new elf.h
header.
Thanks,
Mark