• Austin Clements's avatar
    runtime: inform arena placement using sbrk(0) · bb6309cd
    Austin Clements authored
    On 32-bit architectures (or if we fail to map a 64-bit-style arena),
    we try to map the heap arena just above the end of the process image.
    While we can accept any address, using lower addresses is preferable
    because lower addresses cause us to map less of the heap bitmap.
    
    However, if a program is linked against C code that has global
    constructors, those constructors may call brk/sbrk to allocate memory
    (e.g., many C malloc implementations do this for small allocations).
    The brk also starts just above the process image, so this may adjust
    the brk past the beginning of where we want to put the heap arena. In
    this case, the kernel will pick a different address for the arena and
    it will usually be very high (at least, as these things go in a 32-bit
    address space).
    
    Fix this by consulting the current value of the brk and using this in
    addition to the end of the process image to compute the initial arena
    placement.
    
    This is implemented only on Linux currently, since we have no evidence
    that it's an issue on any other OSes.
    
    Fixes #19831.
    
    Change-Id: Id64b45d08d8c91e4f50d92d0339146250b04f2f8
    Reviewed-on: https://go-review.googlesource.com/39810
    Run-TryBot: Austin Clements <austin@google.com>
    TryBot-Result: Gobot Gobot <gobot@golang.org>
    Reviewed-by: 's avatarIan Lance Taylor <iant@golang.org>
    bb6309cd
sys_linux_ppc64x.s 8.84 KB