ELF info v4 #10

abusque · 2015-08-28T22:34:27Z

This patch set implements a minimal ELF parser to add extra
information necessary for callsite analysis to the statedump and dl
helper.

Also included are unit tests covering x86, x86_64, armeb, and aarch_64
targets.

Changes from version 3:

Handle differing values of p_align between segments when computing memsz
Standardize use of offset_align
Use defines for ELF alignment values instead of constants
Minor style issues

Changes from version 2:

Fixed coding style issues
More rigorous error handling
Field reordering in tracepoints and structs for optimization

Changes from version 1:

More uniform and thorough error handling (i.e. always return -1 on failure,
0 on success)
Make distinction between information not found in ELF file and
actual errors (found status is returned through an out parameter on
function success)
Functions have no side-effects on failure
Add more cases to the unit tests for better coverage
Minor style issues

Implement a minimal ELF parser allowing to compute an executable's in-memory size and to read its build id and debug link info, if any, at runtime. This is performed during base address statedump, and on dlopen when using the `liblttng-ust-dl.so` helper. This adds a `memsz` field to `lttng_ust_statedump:soinfo` and `lttng_ust_dl:dlopen`. Also adds two events to both providers, `build_id` and `debug_link`, which are only traced when the corresponding information is found in the executable file. They can be matched with the corresponding `soinfo` or `dlopen` via the `baddr` field shared amongst all the events. Build ID and debug link are standard methods of identifying and retrieving debug information corresponding to a specific version of an executable. The fields `size` and `mtime` from the existing `soinfo` and `dlopen` events have been removed as they provided no valuable information for analysis, whereas build ID or debug link allow unambiguous retrieval of the debug information, and the on-disk `size` is superseded by the in-memory `memsz`. Signed-off-by: Antoine Busque <[email protected]>

This adds unit tests for UST's ELF parser. Also included are test ELF files for multiple architectures (x86, x86_64, armeb, aarch64_be). The procedure to generate these test files is described in `tests/ust-elf/README.md`. Signed-off-by: Antoine Busque <[email protected]>

compudj · 2015-08-29T02:14:31Z

merged into master, thanks!

Observed issue ============== Applications which transitively dlopen() a library which, in turn, dlopen() providers crash when they are compiled with clang or if LTTNG_UST_ALLOCATE_COMPOUND_LITERAL_ON_HEAP is defined. Core was generated by `././myapp.exe'. Program terminated with signal SIGSEGV, Segmentation fault. #0 0x00007fa94f860bc2 in check_event_provider (probe_desc=<optimized out>) at lttng-probes.c:153 153 if (!check_type_provider(field->type)) { [Current thread is 1 (Thread 0x7fa94fcbc740 (LWP 511754))] (gdb) bt #0 0x00007fa94f860bc2 in check_event_provider (probe_desc=<optimized out>) at lttng-probes.c:153 #1 lttng_ust_probe_register (desc=0x7fa94fe9dc80 <lttng_ust__probe_desc___embedded_sys>) at lttng-probes.c:242 #2 0x00007fa94fe9ba3c in lttng_ust__tracepoints__ptrs_destroy () at /usr/include/lttng/tracepoint.h:590 #3 0x00007fa94fedfe2e in call_init () from /lib64/ld-linux-x86-64.so.2 #4 0x00007fa94fedff1c in _dl_init () from /lib64/ld-linux-x86-64.so.2 #5 0x00007fa94fdf7d45 in _dl_catch_exception () from /usr/lib/libc.so.6 #6 0x00007fa94fee420a in dl_open_worker () from /lib64/ld-linux-x86-64.so.2 #7 0x00007fa94fdf7ce8 in _dl_catch_exception () from /usr/lib/libc.so.6 #8 0x00007fa94fee39bb in _dl_open () from /lib64/ld-linux-x86-64.so.2 #9 0x00007fa94fe8d36c in ?? () from /usr/lib/libdl.so.2 #10 0x00007fa94fdf7ce8 in _dl_catch_exception () from /usr/lib/libc.so.6 #11 0x00007fa94fdf7db3 in _dl_catch_error () from /usr/lib/libc.so.6 #12 0x00007fa94fe8db99 in ?? () from /usr/lib/libdl.so.2 #13 0x00007fa94fe8d3f8 in dlopen () from /usr/lib/libdl.so.2 #14 0x00007fa94fecc647 in mon_constructeur () at mylib.cpp:20 #15 0x00007fa94fedfe2e in call_init () from /lib64/ld-linux-x86-64.so.2 #16 0x00007fa94fedff1c in _dl_init () from /lib64/ld-linux-x86-64.so.2 #17 0x00007fa94fdf7d45 in _dl_catch_exception () from /usr/lib/libc.so.6 #18 0x00007fa94fee420a in dl_open_worker () from /lib64/ld-linux-x86-64.so.2 #19 0x00007fa94fdf7ce8 in _dl_catch_exception () from /usr/lib/libc.so.6 #20 0x00007fa94fee39bb in _dl_open () from /lib64/ld-linux-x86-64.so.2 #21 0x00007fa94fe8d36c in ?? () from /usr/lib/libdl.so.2 #22 0x00007fa94fdf7ce8 in _dl_catch_exception () from /usr/lib/libc.so.6 #23 0x00007fa94fdf7db3 in _dl_catch_error () from /usr/lib/libc.so.6 #24 0x00007fa94fe8db99 in ?? () from /usr/lib/libdl.so.2 #25 0x00007fa94fe8d3f8 in dlopen () from /usr/lib/libdl.so.2 #26 0x00005594f478c18c in main () Cause ===== Building tracepoint instrumentation as C++ using clang causes LTTNG_UST_ALLOCATE_COMPOUND_LITERAL_ON_HEAP to be defined due to a compiler version detection problem addressed by another patch. However, building with LTTNG_UST_ALLOCATE_COMPOUND_LITERAL_ON_HEAP defined still results in the crash. When LTTNG_UST_ALLOCATE_COMPOUND_LITERAL_ON_HEAP is defined, the lttng_ust_event_field lttng_ust__event_fields__[...] structure is initialized by dynamically-allocating field structures for the various fields. As the initialization can't be performed statically, it is performed at run-time _after_ the execution of the library constructors has completed. Moreover, the generated initialization function of the provider (lttng_ust__events_init__[...]) is declared as being a library constructor. Hence, this causes it to run before the tracepoint fields structures has a chance to be initialized. This all results in a NULL pointer dereference during the validation of the fields. Solution ======== When building providers as C++, the initialization function is defined as the constructor of a class. This class is, in turn, instantiated in an anonymous namespace. For the purposes of this patch, the use of an anonymous namespace is equivalent to declaring the instance as 'static', but it is preferred in C++11. Known drawbacks =============== None. References ========== A reproducer is available: https://github.com/jgalar/ust-clang-reproducer Problem initially reported on dotnet/runtime's issue tracker: dotnet/runtime#62398 Relevant LTTng-UST issue: https://bugs.lttng.org/issues/1339 Fixes: #1339 Change-Id: I51cfbe74729bd45e2613a30bc8de17e08ea8233d Signed-off-by: Jérémie Galarneau <[email protected]> Signed-off-by: Mathieu Desnoyers <[email protected]>

Eliminate the following deadlock by calling libc close directly when called from within the 2.12 fd tracker locking. The 2.13 locks always need to be taken outside of the 2.12 locks. In the scenario below, Thread 3 (lttng-ust 2.12 listener thread) takes the locks in the wrong order. Thread 3 (Thread 0x7f7679247700 (LWP 621683) "hello-ust"): #0 __lll_lock_wait (futex=futex@entry=0x7f767a392b60 <ust_safe_guard_fd_mutex>, private=0) at lowlevellock.c:52 lttng#1 0x00007f767a39d843 in __GI___pthread_mutex_lock (mutex=0x7f767a392b60 <ust_safe_guard_fd_mutex>) at ../nptl/pthread_mutex_lock.c:80 -> 2.13 locks fd tracker 2.13 lttng#2 0x00007f767a37ff82 in lttng_ust_lock_fd_tracker_orig () at fd-tracker.c:163 2.13 lttng#3 0x00007f767a380b66 in lttng_ust_safe_close_fd_orig (fd=3, close_cb=0x7f767a56b070 <__GI___close>) at fd-tracker.c:385 2.13 lttng#4 0x00007f767a6e5557 in close (fd=3) at lttng-ust-fd.c:101 2.12 lttng#5 0x00007f767a297e7d in ustcomm_connect_unix_sock (pathname=0x7f767a32bc64 <local_apps+36> "/home/compudj/.lttng/lttng-ust-sock-8", timeout=3000) at lttng-ust-comm.c:157 -> 2.12 listener thread locks fd tracker -> 2.12 listener thread locks ust_lock 2.12 lttng#6 0x00007f767a2a1f77 in ust_listener_thread (arg=0x7f767a32bc40 <local_apps>) at lttng-ust-comm.c:1591 lttng#7 0x00007f767a39aea7 in start_thread (arg=<optimized out>) at pthread_create.c:477 lttng#8 0x00007f767a57aaef in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95 Thread 2 (Thread 0x7f7678a46700 (LWP 621682) "hello-ust"): #0 __lll_lock_wait (futex=futex@entry=0x7f767a32f780 <ust_mutex>, private=0) at lowlevellock.c:52 lttng#1 0x00007f767a39d843 in __GI___pthread_mutex_lock (mutex=0x7f767a32f780 <ust_mutex>) at ../nptl/pthread_mutex_lock.c:80 2.12 lttng#2 0x00007f767a29da59 in ust_lock () at lttng-ust-comm.c:167 2.12 lttng#3 0x00007f767a2a1d95 in ust_listener_thread (arg=0x7f767a329be0 <global_apps>) at lttng-ust-comm.c:1558 lttng#4 0x00007f767a39aea7 in start_thread (arg=<optimized out>) at pthread_create.c:477 lttng#5 0x00007f767a57aaef in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95 Thread 1 (Thread 0x7f767a33a040 (LWP 621681) "hello"): #0 __lll_lock_wait (futex=futex@entry=0x7f767a32f720 <ust_safe_guard_fd_mutex>, private=0) at lowlevellock.c:52 lttng#1 0x00007f767a39d843 in __GI___pthread_mutex_lock (mutex=0x7f767a32f720 <ust_safe_guard_fd_mutex>) at ../nptl/pthread_mutex_lock.c:80 -> 2.12 lock fd tracker 2.12 lttng#2 0x00007f767a29c37c in lttng_ust_lock_fd_tracker () at lttng-ust-fd-tracker.c:153 2.12 lttng#3 0x00007f767a29ceba in lttng_ust_safe_close_fd (fd=4, close_cb=0x7f767a56b070 <__GI___close>) at lttng-ust-fd-tracker.c:341 2.13 lttng#4 0x00007f767a380b06 in lttng_ust_safe_close_fd_chain (fd=4, close_cb=0x7f767a56b070 <__GI___close>) at fd-tracker.c:348 2.13 lttng#5 0x00007f767a380b5c in lttng_ust_safe_close_fd_orig (fd=4, close_cb=0x7f767a56b070 <__GI___close>) at fd-tracker.c:379 2.13 lttng#6 0x00007f767a6e5557 in close (fd=4) at lttng-ust-fd.c:101 -> 2.13 lock fd tracker 2.13 lttng#7 0x00007f767a43b5e6 in lttng_ust_elf_destroy (elf=0x55b870f044c0) at elf.c:352 2.13 lttng#8 0x00007f767a3f2797 in get_elf_info (bin_data=0x7ffd5481ef70) at lttng-ust-statedump.c:296 2.13 lttng#9 0x00007f767a3f283f in extract_baddr (bin_data=0x7ffd5481ef70) at lttng-ust-statedump.c:319 2.13 lttng#10 0x00007f767a3f3173 in extract_bin_info_events (info=0x7ffd5481fff0, size=64, _data=0x7ffd54820098) at lttng-ust-statedump.c:518 lttng#11 0x00007f767a5b3ad5 in __GI___dl_iterate_phdr (callback=0x7f767a3f2f5a <extract_bin_info_events>, data=0x7ffd54820098) at dl-iteratephdr.c:75 2.13 lttng#12 0x00007f767a3f32c5 in lttng_ust_dl_update_orig (ip=0x7f767a3cb599 <lttng_ust_ctor+683>) at lttng-ust-statedump.c:574 2.13 lttng#13 0x00007f767a3f33f7 in lttng_ust_statedump_init () at lttng-ust-statedump.c:638 2.13 lttng#14 0x00007f767a3cb599 in lttng_ust_ctor () at lttng-ust-comm.c:2246 2.13 lttng#15 0x00007f767a3ccaad in lttng_ust_after_fork_child (restore_sigset=0x7ffd548207e0) at lttng-ust-comm.c:2577 2.13 lttng#16 0x00007f767a6f687f in fork () at ustfork.c:271 lttng#17 0x000055b8705f1034 in make_child () lttng#18 0x000055b8705daacc in execute_command_internal () lttng#19 0x000055b8705ddcf5 in execute_command () lttng#20 0x000055b8705df951 in ?? () lttng#21 0x000055b8705daf79 in execute_command_internal () lttng#22 0x000055b8705ddcf5 in execute_command () lttng#23 0x000055b8705c49db in reader_loop () lttng#24 0x000055b8705c3668 in main () Getting the state of lttng-ust 2.12 ust_fd_mutex_nest TLS variable is not straightforward, because it is a static variable (internal state). The trick used here is to rely on the "lttng_ust_safe_close_fd" symbol exported by lttng-ust 2.12. When passed fd=-1, with a close_cb which simply returns 0, we can use the resulting return values to determine the current state (zero vs nonzero) of the ust_fd_mutex_nest TLS variable without any side-effect other than temporarily taking/releasing the fd tracker lock when ust_fd_mutex_nest==0. Signed-off-by: Mathieu Desnoyers <[email protected]> Change-Id: I6b95e0fd607abccd67aadf35ec96c19877394b16

abusque added 2 commits August 28, 2015 17:53

abusque closed this Aug 29, 2015

abusque deleted the elf-info-v4 branch August 31, 2015 01:47

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ELF info v4 #10

ELF info v4 #10

abusque commented Aug 28, 2015

compudj commented Aug 29, 2015

ELF info v4 #10

ELF info v4 #10

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abusque commented Aug 28, 2015

compudj commented Aug 29, 2015