[Bug gold/14149] New: The _end symbol is not properly aligned

[jhb at FreeBSD dot org]

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: address@hidden
        ReportedBy: address@hidden
                CC: address@hidden
    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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