Linux + Clang + execstack

[Arthur Eubanks]

Hi,

At Google we're trying to build hotspot on Linux with clang. One thing that
happens is that the resulting libjvm.so is stack executable. When running
hotspot we get warnings about the stack being executable.

Compiling an assembly file into the final .so results in the stack being
executable. In this case the file is linux_x86_64.s. This doesn't happen
with gcc because "-Wl,-z,noexecstack" is passed as a hotspot linker flag
with gcc in flags-ldflags.m4. When using clang that linker flag isn't
passed.

Doing something like the solution in
https://wiki.ubuntu.com/SecurityTeam/Roadmap/ExecutableStacks
fixes the problem without the use of linker flags.

The jtreg test test/hotspot/jtreg/runtime/execstack/TestCheckJDK.java
checks for the stack being executable.

Any thoughts? If there are no objections, I can propose a patch that works
for both gcc and clang on Linux. Also, I'm not sure how/if macOS handles
this problem given that it uses clang.