[llvm-dev] some questions on libunwind

[Schrodinger ZHU Yifan via llvm-dev]

Hi,

These questions were originally posted on Discord but I have got no reply at all so I am writing this email to post the questions to the developer list.

Background

1.  https://github.com/jemalloc/jemalloc/issues/585
2.  https://reviews.llvm.org/D9744
3.  My team was implementing a database and we planned to add a debug tool for memory profiling when jemalloc is enabled. However, nongnu libunwind caused deadlock from time to time when used together with jeprof.
4. I am in charge of migrating my team's toolchain from GCC to LLVM; besides clang, we want to make all of our runtimes (except libc, for the time being) in LLVM, including libcxx, omp, compiler-rt, libunwind

My problems:
1. libunwind.h is provided in the LLVM repo, but I am curious that why it is not an installation target. Currently, my solution to vendor a LLVM's header within my team's repo.
2. nongnu implementation exposes a specialized unw_init_local2 for stack capturing initiated at signal frame, but this function is not provided at LLVM's world. According to the test cases in LLVM's repo, I inferred that LLVM does not need user to specify the signal frame argument. Is this true?
3. Is there any previous discussion in LLVM side on the deadlock situation of jemalloc and libunwind?

Best wishes.

Schrodinger ZHU Yifan
School of Data Science, CUHK(SZ)
Website: https://github.com/schrodingerzhu
Github: SchrodingerZhu
Twitter: ZhuSchrodinger

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