[lldb-dev] Linux issues where I am not getting breakpoints...

[Tamas Berghammer via lldb-dev]

See https://bugs.llvm.org/show_bug.cgi?id=25806 for details about why we
can't set breakpoint in the static initializer (it is an LLDB bug).

For your investigation a few pointers/guesses (assuming it is not some
stdout displaying issue what I consider unlikely based on your description):
* Do your application calls dlopen? It can explain why you see stdout
before some library load events and also I can imagine more issue in that
code path.
* Are you sure LoadModuleAtAddress called from LoadAllCurrentModules in all
4 cases? It can be called from RefreshModules as well what is used when we
get notified about a new library and I expect it to be more likely based on
the output (for the second 2 line).
* I suggest to stop at libc.so'_start and see what libraries are loaded
there (I expect it to be after the first 2 log and before the stdout).
Verify that both shared-library-event breakpoint is resolved at this time
(by "breakpoint list -i") and also set a manual breakpoint there to see
when it triggers. I expect you will hit that breakpoint just after your log
lines are displayed. If that is the case you should get a stacktrace and
see the callstack causing the event to be triggered.
* The libraries you should look out in the log is libc.so and
ld-linux-x86-64.so
(or similar). The dynamic loader integration should work only after these 2
libraries are loaded.

On Tue, Apr 11, 2017 at 3:56 PM Greg Clayton via lldb-dev <
lldb-dev at lists.llvm.org> wrote:

> On Apr 11, 2017, at 5:33 AM, Pavel Labath <labath at google.com> wrote:
>
> Are you sure this is not just an artifact of stdio buffering? I tried the
> same experiment, but I placed a real log statement, and I could see that
> all the LoadModuleAtAddress calls happen between the $T and $c packets in
> the gdb-remote packet sequence.
>
> The module loading should be synchronous, so I think the problem lies
> elsewhere.
>
> What is the nature of the breakpoint that is not getting hit? Can you
> provide a repro case? The only bug like this that I am aware of is that we
> fail to hit breakpoints in global constructors in shared libraries, but
> that hasn't worked even in 3.8..
>
>
> I unfortunately can't attach a repro case. I will be able to track this
> down, just need some pointers. I did notice that I wasn't able to hit
> breakpoints in global constructors though... Do we know why? On Mac, we get
> notified of shared libraries as they load so we never miss anything. Why
> are we not able to get the same thing with linux?
>
>
>
> On 10 April 2017 at 22:51, Greg Clayton via lldb-dev <
> lldb-dev at lists.llvm.org> wrote:
>
> I have added some logging to a program that is not hitting breakpoints
> with LLDB top of tree SVN. An older lldb 3.8 hits the breakpoint just fine.
> I placed some logging in LLDB:
>
> ModuleSP DynamicLoader::LoadModuleAtAddress(const FileSpec &file,
>                                             addr_t link_map_addr,
>                                             addr_t base_addr,
>                                             bool base_addr_is_offset) {
>   printf("%s: lma = 0x%16.16llx, ba = 0x%16.16llx, baio = %i\n",
> file.GetPath().c_str(), link_map_addr, base_addr, base_addr_is_offset);
>
>
> This is called by DynamicLoaderPOSIXDYLD::LoadAllCurrentModules().
>
> My problem is I see:
>
> [vdso]: lma = 0xffffffffffffffff, ba = 0x00007ffff7ffa000, baio = 0
> linux-vdso.so.1: lma = 0x00007ffff7ffe6e0, ba = 0x00007ffff7ffa000, baio =
> 1
> /tmp/liba.so: lma = 0x00007ffff7ff66a8, ba = 0x00007ffff7e30000, baio = 1
> 8 locations added to breakpoint 1
> /tmp/libb.so: lma = 0x00007ffff7e2f000, ba = 0x00007ffff7d43000, baio = 1
> [==========] Running 14 tests from 1 test case.
> [----------] Global test environment set-up.
> [----------] 14 tests from MyTest
> [ RUN      ] MyTest.Test1
> [       OK ] MyTest.Test1 (0 ms)
> /tmp/libc.so: lma = 0x00007ffff7e2f000, ba = 0x00007ffff7d43000, baio = 1
> /tmp/libd.so: lma = 0x00007ffff7e2f000, ba = 0x00007ffff7d43000, baio = 1
>
>
> Note that I see program output _during_ the messages that are showing that
> shared libraries are being loaded? I would assume we are loading shared
> libraries synchronously, but the log seems to indicated otherwise.
>
> If anyone knows anything on this subject please let me know...
>
> Greg Clayton
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