[cfe-dev] PCH generated in a different environment crashes application

Richard Smith via cfe-dev cfe-dev at lists.llvm.org
Tue Oct 9 11:55:52 PDT 2018

On Tue, 9 Oct 2018 at 08:17, Geoff Levner via cfe-dev <
cfe-dev at lists.llvm.org> wrote:

> We have an application that uses Clang and an Orc-based JIT to compile
> and run C++ code on the fly. To speed up compilation, the application
> generates a .h file that includes all the required header files, then
> precompiles it to a PCH file. So if the code changes afterward, but
> the includes don't, the PCH file can be reused.
> That works fine when I work on my own. But if another user on another
> machine generates the PCH file, the application crashes, both for me
> and for the other user, as soon as the compiled function is invoked. I
> haven't been able to determine yet what difference in the other user's
> environment might cause the problem.
> Does anybody on this list have any idea why a PCH file generated by
> another user with exactly the same command line might cause a crash?
> I don't know if it's relevant, but the application is compiled with
> clang/llvm 7.0.0. It uses a GeneratePCHAction to generate the PCH
> file, and it uses a VerifyPCHAction if the PCH file already exists.
> The VerifyPCHAction succeeds, in this case, but the compiled function
> still crashes.

VerifyPCHAction specifies AllowConfigurationMismatch = true, so it doesn't
provide a full check that the PCH is actually usable. Do you also set
AllowConfigurationMismatch or DisablieValidation to true when creating the
ASTReader to load the PCH file? (How are you loading it? If via code, what
are you calling and what arguments are you passing, and if via the clang
driver, what flags are you using?)
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