[lldb-dev] Further Linux adventures

Joel Dillon joelrdillon at gmail.com
Sun Oct 30 13:07:10 PDT 2011

There was another stray plain int I'd missed in the code that reads
registers, truncating the PC.
The attached patch makes lldb compile (modulo some link ordering dependency
problems that
I don't have enough cmake-fu to fix properly) and work on Linux (and as a
bonus prevents a
segfault when attempting to attach to a running process, though that
functionality appears
to be unimplemented as yet). I also added some extra logging for ptrace
that helped me catch
some of the problems.

On Thu, Oct 27, 2011 at 12:54 PM, Greg Clayton <gclayton at apple.com> wrote:

> The darwin ptrace call looks from <sys/ptrace.h> looks like:
> int ptrace(int _request, pid_t _pid, caddr_t _addr, int _data);
> I never try to use "int" "long" as types when programming in LLDB and we
> would try to exclusively use "uint*_t" and "int*_t" where the type is
> explicit. The only exception to the rule is if you are wrapping an API
> (like say "ptrace") where it returns a specific type in the header file
> ("int" in our header file). If the return types differ from system to
> system, we should templatize the code the uses it.
> So overall we should try to use the explicitly sized integer typedefs from
> stdint.h (uint8_t, uint16_t, uint32_t, etc) to avoid any such issues. It
> sounds like there are some issues in the Linux plug-in. The function is:
> void
> LinuxThread::BreakNotify(const ProcessMessage &message)
> {
>    bool status;
>    LogSP log (ProcessLinuxLog::GetLogIfAllCategoriesSet
>    assert(GetRegisterContextLinux());
>    status = GetRegisterContextLinux()->UpdateAfterBreakpoint();
>    assert(status && "Breakpoint update failed!");
>    // With our register state restored, resolve the breakpoint object
>    // corresponding to our current PC.
>    assert(GetRegisterContext());
>    lldb::addr_t pc = GetRegisterContext()->GetPC();
>    if (log)
>        log->Printf ("LinuxThread::%s () PC=0x%8.8llx", __FUNCTION__, pc);
>    lldb::BreakpointSiteSP
> bp_site(GetProcess().GetBreakpointSiteList().FindByAddress(pc));
>    assert(bp_site);
>    lldb::break_id_t bp_id = bp_site->GetID();
>    assert(bp_site && bp_site->ValidForThisThread(this));
>    m_breakpoint = bp_site;
>    m_stop_info = StopInfo::CreateStopReasonWithBreakpointSiteID(*this,
> bp_id);
> }
> Liiks like the PC is read from the register context and there doesn't seem
> to be a breakpoint site. Enable the logging before you run:
> (lldb) log enable plugin.process.linux thread
> (lldb) run
> This should cause the PC to be logged. Then you should check that a
> software breakpoint was indeed set at this location. You might also want to
> verify that no one removed the breakpoint site after stopping?
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