Function frameCallback

src/pystack/_pystack/unwinder.cpp:78–140

}

static int
frameCallback(Dwfl_Frame* state, void* arg)
{
    auto* frames = static_cast<std::vector<Frame>*>(arg);
    Dwarf_Addr pc;
    bool isActivation;
    if (!dwfl_frame_pc(state, &pc, &isActivation)) {
        LOG(DEBUG) << "dwfl_frame_pc failed";
        return -1;
    }

    std::optional<Dwarf_Word> stackPointer;
    // Unwinding through musl libc with elfutils can get stuck returning the
    // same PC in a loop forever.
    //
    //   https://sourceware.org/bugzilla/show_bug.cgi?id=30272
    //   https://marc.info/?l=musl&m=168053842303968&w=2
    //
    // We can work around this by asking elfutils what the stack pointer is for
    // each frame and breaking out on our own if two different frames report
    // the same stack pointer. When PyStack is built with glibc and not built
    // with a recent enough version of elfutils for us to do this check, we
    // skip it. This isn't entirely correct, as it means that a PyStack built
    // with glibc and an old elfutils can fail to collect stacks for Python
    // interpreters built against musl libc, but it avoids a hard dependency on
    // a newer version of elfutils than most distros have available. It's
    // unlikely that users will encounter problems, but if they do, the simple
    // work around is to install PyStack using the same interpreter they want
    // to get stacks for, or to build with a more recent version of elfutils.

#if _ELFUTILS_VERSION >= 188 or (defined(__linux__) && !defined(__GLIBC__))

    // These platform specific magic numbers are part of the platform ABI.
    // For any platform not handled below we never look up the value of the
    // stack pointer register, and so never return DWARF_CB_ABORT.
    std::optional<unsigned int> stackPointerRegNo;
#    if defined(__x86_64__)
    // https://refspecs.linuxbase.org/elf/x86_64-abi-0.99.pdf
    // Figure 3.36: DWARF Register Number Mapping
    stackPointerRegNo = 7;
#    elif defined(__aarch64__)
    // https://refspecs.linuxfoundation.org/ELF/ppc64/PPC-elf64abi.html#DW-REG
    stackPointerRegNo = 31;
#    endif

    if (stackPointerRegNo) {
        stackPointer.emplace(0);
        if (0 != dwfl_frame_reg(state, stackPointerRegNo.value(), &stackPointer.value())) {
            throw UnwinderError("Invalid register number!");
        }
    }

    if (!frames->empty() && pc == frames->back().pc && isActivation == frames->back().isActivation
        && stackPointer && stackPointer == frames->back().stackPointer)
    {
        LOG(DEBUG) << std::hex << std::showbase << "Breaking out of (infinite?) unwind loop @ " << pc;
        return DWARF_CB_ABORT;
    }