On Friday, 21 July 2017 at 20:53:18 UTC, Walter Bright wrote:
On 7/21/2017 12:06 PM, Johan Engelen wrote:
< [...]
Thanks for your work on this. It is important to support such
valuable tools.
One way making such things pretty much cost-free in the olden
days was to trick the linker into writing NOPs over the
function calls by using specially crafted fixup records. This
worked with dumb linkers, but today's linkers do much more
semantic inference into what's going on, I'm afraid this may be
too brittle.
Unless there is a linker feature to support it? Are some
linkers able to NOP out a function call if it sees that the
function body consists solely of a RET?
ARM's toolchain has something that does this:
http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.faqs/ka14171.html
Can't find something like it for other toolchains.
Another option is to use a pointer to the asan functions, like:
if (asan_fp)
(*asan_fp)(args...)
The asan_fp can then be set to NULL and there's only the
overhead of a compare/branch rather than a function call. Well,
also the load of a global variable.
I can mark the if-clause as unlikely, so the performance
difference would be small (allocation is slow already, of course).
Let me try that for now. We can decide later, let's first find an
implementation that works and test that the whole idea is valid
and I didn't miss anything important.
Can you advise me on where best to add the asan calls?
Thanks,
Johan
PS. The interface is easy, I don't need much info at the call
sites:
// Poisons memory region [addr, addr+size)
void __asan_poison_memory_region(const(void*) addr, size_t size);
// Unpoisons memory region [addr, addr+size)
void __asan_unpoison_memory_region(const(void*) addr, size_t
size);
