[PATCH] D32846: [XRay][compiler-rt] Add function id utilities for XRay

[David Blaikie via llvm-commits]

On Thu, May 4, 2017 at 4:53 PM Dean Michael Berris via Phabricator <
reviews at reviews.llvm.org> wrote:

> dberris marked an inline comment as done.
> dberris added a comment.
>
> In https://reviews.llvm.org/D32846#746274, @dblaikie wrote:
>
> > Slightly curious to me that function IDs are > 0, but use a signed type
> - but no big deal, I guess there's probably a reason.
>
>
> I agonised over this for a while. There's no real reason why it's signed,
> but changing it now might be too late (unless we start doing XRay
> versioning of the sleds). It's hard to assume that when we're laying down
> bytes in the binary with the compiler that signed numbers and unsigned
> numbers have the same representation (maybe they are for one platform,
> while not in another).
>
> I suspect we can change it. Probably should do it a later time though. :)
>
>
>
> ================
> Comment at: test/xray/TestCases/Linux/func-id-utils.cc:26-28
> +  // CHECK-LABEL: addresses:
> +  // CHECK: #[[MAX]] -> @[[ADDR:.*]]
> +  // CHECK-NOT: #0 -> @{{.*}}
> ----------------
> dblaikie wrote:
> > What does this test?
> >
> > Should the test case print the &foo and &bar, or
> assert(xray_function_address(1) == &foo), etc?
> It does look a little goofy, but it's testing that:
>
> - We do have functions instrumented (i.e. __xray_max_function_id() != 0).
> - The maximum function id has an address associated with it.
> - We don't have a function id 0 that has an address. :)
>
> While it's tempting to print the addresses of function id's and check,
> unfortunately we cannot assume that the compiler/linker will lay out the
> functions in a stable manner -- and thus function id's won't be guaranteed
> to always be mapped to specific function name.
>

Sort them?

But also I was thinking more having the code itself check, rather than
print and check with FileCheck?

  std::set<void*> original = {&foo, &bar};
  // build similar set from the xray_function_address calls
  if original != xray
    return 1;

that sort of thing.


>
>
> https://reviews.llvm.org/D32846
>
>
>
>
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