http://sourceware.org/bugzilla/show_bug.cgi?id=14149
Bug #: 14149
Summary: The _end symbol is not properly aligned
Product: binutils
Version: 2.22
Status: NEW
Severity: normal
Priority: P2
Component: gold
AssignedTo: i...@airs.com
ReportedBy: j...@freebsd.org
CC: ccout...@google.com
Classification: Unclassified
I have reproduced this with the gold linker from both 2.21 and 2.22. I have
reproduced this using GCC versions 4.5.3, 4.6.4, and 4.7.0 on both FreeBSD
8.2-STABLE and 9.0-STABLE. To reproduce, compile the following test program
and link with gold:
#include <stdio.h>
#include <new>
void foo()
{
char *c = new(std::nothrow) char[10];
delete c;
}
int
main()
{
printf("Hello world\n");
}
Use objdump -T to obtain the offset of '_end':
a.out: file format elf64-x86-64-freebsd
DYNAMIC SYMBOL TABLE:
0000000000401ac8 g DO .bss 0000000000000008 Base environ
0000000000401a80 g DO .data 0000000000000008 Base __progname
0000000000000000 DF *UND* 0000000000000000 GLIBCXX_3.4
_ZnamRKSt9nothrow_t
0000000000000000 DF *UND* 0000000000000000 GLIBCXX_3.4 _ZdlPv
0000000000000000 DF *UND* 0000000000000000 FBSD_1.0 atexit
0000000000000000 DF *UND* 0000000000000000 FBSD_1.0 exit
0000000000000000 DF *UND* 0000000000000000 FBSD_1.0 _init_tls
0000000000000000 w D *UND* 0000000000000000
_Jv_RegisterClasses
0000000000401ad0 g DO .bss 0000000000000001 GLIBCXX_3.4 _ZSt7nothrow
0000000000000000 DF *UND* 0000000000000000 FBSD_1.0 puts
0000000000401ad1 g D *ABS* 0000000000000000 Base _end
Note that _end has a mis-aligned address. This causes jemalloc (the malloc in
FreeBSD's libc) to corrupt it's internal RB trees as it assumes the start of
the heap is aligned on at least an even address. Using ld.bfd results in _end
being aligned on an 8-byte boundary. The linker scripts for ld.bfd for FreeBSD
explicitly pad _end to an 8 byte boundary, so I assume it is a bug for the gold
linker to not do this.
The bug appears to be triggered by std::nothrow pulling in a reference to a 1
byte symbol at the end of the BSS.
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