[lld] r264115 - Avoid memcpy from nullptr. NFC.

[David Blaikie via llvm-commits]

On Tue, Mar 22, 2016 at 3:59 PM, Pete Cooper via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

> Author: pete
> Date: Tue Mar 22 17:59:35 2016
> New Revision: 264115
>
> URL: http://llvm.org/viewvc/llvm-project?rev=264115&view=rev
> Log:
> Avoid memcpy from nullptr.  NFC.
>
> This was caught by the UBSan bot.  When the atom has no size, we would
> issue a memcpy with size0 and a nullptr for the source.
>
> Also, this code should never have references inside an empty atom so
> add an assert for that while we're here.
>
> Modified:
>     lld/trunk/lib/ReaderWriter/MachO/ArchHandler_x86.cpp
>
> Modified: lld/trunk/lib/ReaderWriter/MachO/ArchHandler_x86.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/lld/trunk/lib/ReaderWriter/MachO/ArchHandler_x86.cpp?rev=264115&r1=264114&r2=264115&view=diff
>
> ==============================================================================
> --- lld/trunk/lib/ReaderWriter/MachO/ArchHandler_x86.cpp (original)
> +++ lld/trunk/lib/ReaderWriter/MachO/ArchHandler_x86.cpp Tue Mar 22
> 17:59:35 2016
> @@ -420,6 +420,11 @@ void ArchHandler_x86::generateAtomConten
>                                            FindAddressForAtom
> findSectionAddress,
>                                            uint64_t imageBaseAddress,
>                                            uint8_t *atomContentBuffer) {
> +  if (!atom.size()) {
> +    assert(atom.begin() == atom.end() &&
> +           "Cannot have references without content");
>

Um, that seems like a problematic API, if size can be distinct from end() -
begin() ? Perhaps some of these should be renamed to avoid confusion?


> +    return;
> +  }
>    // Copy raw bytes.
>    memcpy(atomContentBuffer, atom.rawContent().data(), atom.size());
>    // Apply fix-ups.
>
>
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