[PATCH] D59264: [Driver] Support compiler-rt crtbegin.o/crtend.o for Linux

Ethan Sommer via Phabricator via cfe-commits cfe-commits at lists.llvm.org
Wed Mar 13 05:33:12 PDT 2019

E5ten added inline comments.

Comment at: clang/lib/Driver/ToolChains/Gnu.cpp:563
+          crtend = Args.hasArg(options::OPT_shared) || IsPIE || IsStaticPIE ?
+              "crtend_shared" : "crtend";
+          CmdArgs.push_back(ToolChain.getCompilerRTArgString(
phosek wrote:
> MaskRay wrote:
> > phosek wrote:
> > > MaskRay wrote:
> > > > I believe `crtbegin.o` `crtend.o` should just work. It is not necessary to use `crtbegin_shared.o` `crtend_shared.o`.
> > > This is related to your comments on D28791, specifically that we should be using `crtbegin_shared.o` for `-shared` or `-pie` and `crtbegin.o` otherwise, is that not the case?
> > Yes. I think we can rename `crtbegin_shared.o` to `crtbegin.o` and use it for every configuration: `-no-pie` `-pie` `-shared` `-static` `-static -pie`.
> We've checked the glibc implementation of `__cxa_finalize`. A nonzero `__dso_handle` has to match the value passed to `__cxa_atexit` but a zero `__dso_handle` matches every function registered. So it matters that DSO fini calls use `&__dso_handle` to match their registrations for the `dlclose` case, but it also matters that the main executable fini call use zero to run all the dtors at exit time. It's not clear it really needs to be that way, but it would affect how the dtors get run which might affect some use cases. Hence, I don't think we can combine `crtbegin.o` and `crtbegin_shared.o`.
I may be wrong but from what I can see crtend and crtend_shared are identical, so while the crtbegins must stay separate can't the 2 crtends be merged into one that gets used in all cases instead of having a duplicate object under a different name?

  rC Clang



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