modified:   __init__.py

* get_kprobe_functions(): detect more non-attachable functions

Improve get_kprobe_functions() to exclude more non-attachable functions
like IRQ routines and functions in kernel modules blacklisted via
NOKPROBE_SYMBOLS().
Signed-off-by: Andrea Righi <righi.andrea@gmail.com>

* get_kprobe_functions: fix bytes/str type error
Signed-off-by: Andrea Righi <righi.andrea@gmail.com>

manpage: remove non-existent -p option from the biotop manpage

The biotop manpage references a -p option that the tools doesn't have,
and AFAICT, never had. It's only referenced in the manpage option, not
in the synopsis, in "biotop -h" output not biotop_example.txt.

Enables linking bcc-static in binaries compiled with rtti

When ausyscall is used as a fallback plan to generate the
syscall map, the subprocess.check_output() call fails as
the program name and arguments must be passed separately.

Fixes: 218f7482 ("Wcohen/efficiency (#2063)")
Signed-off-by: Sandipan Das <sandipan@linux.ibm.com>

Recent -next kernels don't have blk_start_request() function
anymore. It has been removed in a recent cleanup. bio* tools should be
able to handle the lack of this probe.

* Reduce instrumentation overhead with the sys_enter and sys_exit tracepoints

The ucalls script initially used kprobes and kretprobes on each of the
hundreds of syscalls functions in the system.  This approach causes a
large number of probes to be set up at the start and removed at the
conclusion of the script's execution resulting in slow start up.

Like the syscount.py script the ucall syscall instrumentation has been
modified to use the sys_enter and sys_exit tracepoints.  This only
requires the installation and removal of one or two tracepoints to
implement and results in much shorter times to start and stop the
ucalls script.

Another benefit of this change is syscalls on newer kernels will be
monitored with the "-S" option.  The regular expression used to find
the locations for the kprobes and kretprobes for all the possible
syscall functions would not would match the syscall function naming
convention in newer kernels.

* Update ucalls_examples.txt to match current "-S" option output

* Add required "import subprocess" and remove unneeded "global syscalls"

* Factor out the syscall_name code into a separate python module syscall.py

Multiple scripts are going to find the syscall_name() function useful
when using the syscall tracepoints.  Factoring out this code into a
separate python module avoids having to replicate this code in
multiple scripts.

* Use the syscall_name() function in syscount.py to make it more compact.

* Update the default syscall mappings and the way that they were generated

The default table was missing some newer syscall mapping. Regenerated
the table using the syscallent.h file from Fedora 30
strace-4.25-1.fc30.src.rpm.  Also updated the comment with the command
actually used to generate the mappings.

* Add license information and upsdate the syscalls

The default x86_64 syscall dictionary mapping syscalls numbers to
names has been updated. The following syscall x86_64 names have been
updated:

    18: b"pwrite64",
    60: b"exit",
    166: b"umount2",

The following syscall x86_64 have been added:

    313: b"finit_module",
    314: b"sched_setattr",
    315: b"sched_getattr",
    316: b"renameat2",
    317: b"seccomp",
    318: b"getrandom",
    319: b"memfd_create",
    320: b"kexec_file_load",
    321: b"bpf",
    322: b"execveat",
    323: b"userfaultfd",
    324: b"membarrier",
    325: b"mlock2",
    326: b"copy_file_range",
    327: b"preadv2",
    328: b"pwritev2",
    329: b"pkey_mprotect",
    330: b"pkey_alloc",
    331: b"pkey_free",
    332: b"statx",
    333: b"io_pgetevents",
    334: b"rseq",

* Eliminate stderr output and use of shell features

Redirect all stderr output so it isn't seen.  Also avoid use of the
shell pipe and tail command.  Just strip off the first line in the
python code instead.

* Update lib/ucalls.py smoke test to required linux-4.7

The use of tracepoints in the ucalls.py requires linux-4.7. Changed
the test to only run with a suitable kernel.  The libs/ucalls.py
script is no longer inserting hundreds of kprobes and is much faster
as a result, so removed the timeout adjustment and the comment about
it being slow.

This reverts commit 5b76047f.

The code is actually not duplicated. It is used to process
double vlan's. See comments in:
  https://github.com/iovisor/bcc/pull/1493

With latest llvm/clang, we have the following compilation errors:

    /home/yhs/work/bcc2/src/cc/frontends/clang/b_frontend_action.cc:
      In member function ‘bool ebpf::BTypeVisitor::VisitVarDecl(clang::VarDecl*)’:
    /home/yhs/work/bcc2/src/cc/frontends/clang/b_frontend_action.cc:1130:52:
      error: no matching function for call to ‘clang::Expr::EvaluateAsInt(llvm::APSInt&, clang::ASTContext&)’
               if (I->getInit(idx)->EvaluateAsInt(res, C)) {
                                                    ^
    /home/yhs/work/bcc2/src/cc/frontends/clang/b_frontend_action.cc:1130:52: note: candidate is:
    In file included from /home/yhs/work/llvm/build/install/include/clang/AST/Attr.h:19:0,
                 from /home/yhs/work/llvm/build/install/include/clang/AST/TypeLoc.h:18,
                 from /home/yhs/work/llvm/build/install/include/clang/AST/ASTTypeTraits.h:24,
                 from /home/yhs/work/llvm/build/install/include/clang/AST/ASTContext.h:18,
                 from /home/yhs/work/bcc2/src/cc/frontends/clang/b_frontend_action.cc:23:
    /home/yhs/work/llvm/build/install/include/clang/AST/Expr.h:604:8:
      note: bool clang::Expr::EvaluateAsInt(clang::Expr::EvalResult&, const clang::ASTContext&,
              clang::Expr::SideEffectsKind) const
       bool EvaluateAsInt(EvalResult &Result, const ASTContext &Ctx,
        ^

The error is introduced by the following commit:
https://reviews.llvm.org/rL348053

Basically, the clang FieldDecl method EvaluateAsInt signature got
changed and there is no compatible way in the llvm/clang
to also work in the old versions. So this patch just provided
a new implementation to get field value for llvm version 8 and later.
Signed-off-by: Yonghong Song <yhs@fb.com>

Mostly a cut and paste of the xdp_drop_count.py with needed changes for
doing a source and destination MAC swap.
Signed-off-by: Andy Gospodarek <gospo@broadcom.com>

There have been some updates the code in the examples.  The tutorial
text should match up with the current example code. In particular we
want to make ensure that the probe for the syscall functions match up
with what is currently needed for newer kernels that do not have
syscall functions uniformly start with "sys_".

* tcpstates: Add systemd journal logging.

Add a -Y/--journal flag to tcpstates.py, which logs events to the
systemd journal.

* tcpstates: Document systemd journal logging.

Update tcpstates_example.txt and tcpstates.8 to include the "-Y" flag.

auto select current release for ubuntu

Snapcraft has an improved mechanism for wrapping python executables.
Remove all the older snapcraft legacy cruft and update for the new
snapcraft tooling.
Signed-off-by: Colin Ian King <colin.king@canonical.com>

Otherwise, if llvm is built with assertion on,
we will hit the following error for a simple trace.py script like
  -bash-4.4$ sudo ./trace.py 'SyS_nanosleep'
  python: /home/yhs/work/llvm/lib/ExecutionEngine/MCJIT/MCJIT.cpp:204:
          virtual void llvm::MCJIT::generateCodeForModule(llvm::Module*):
          Assertion `M->getDataLayout() == getDataLayout() && "DataLayout Mismatch"'
          failed.
  Aborted (core dumped)
  -bash-4.4$
Signed-off-by: Yonghong Song <yhs@fb.com>

Sync compat/linux/{bpf.h, bpf_common.h, virtual_bpf.h}
with latest bpf-next. The change in bpf_common.h are comments only.
Signed-off-by: Yonghong Song <yhs@fb.com>

In folded output format when both kernel and user stacks are missing,
the message "[Missing User Stack]" is formatted incorrectly, for example:

chrome;entry_SYSCALL_64_after_hwframe;do_syscall_64;SyS_poll;do_sys_poll;poll_schedule_timeout;schedule_hrtimeout_range;schedule_hrtimeout_range_clock;schedule;--;[Missed Kernel Stack];[;M;i;s;s;e;d; ;U;s;e;r; ;S;t;a;c;k;];fio 4955989

This is because we're incorrectly appending the missing stack message in
the list of stack entries. Fix by appending the message as a single item.
Signed-off-by: Andrea Righi <righi.andrea@gmail.com>

Also, fix an incorrect indentation in the same block.

* Allow unused return value in cc source

With llvm-7.0.0,
some annoying warning messeges are raised:

	/home/lecopzer/workspace/bcc/src/cc/libbpf.c:456:3: warning: ignoring return value of ‘fgets’, declared with attribute warn_unused_result [-Wunused-result]
   	fgets(fmt, sizeof(fmt), f); // pos
   	^~~~~~~~~~~~~~~~~~~~~~~~~~

/home/lecopzer/workspace/bcc/src/cc/libbpf.c: In function ‘bpf_prog_get_tag’:
/home/lecopzer/workspace/bcc/src/cc/libbpf.c:456:3: warning: ignoring return value of ‘fgets’, declared with attribute warn_unused_result [-Wunused-result]
   fgets(fmt, sizeof(fmt), f); // pos
   ^~~~~~~~~~~~~~~~~~~~~~~~~~
...

/home/lecopzer/workspace/bcc/tests/cc/utils.cc: In function ‘int cmd_scanf(const char*, const char*, ...)’:
/home/lecopzer/workspace/bcc/tests/cc/utils.cc:30:10: warning: ignoring return value of ‘int vfscanf(FILE*, const char*, __va_list_tag*)’, declared with attribute warn_unused_result [-Wunused-result]
   vfscanf(pipe, fmt, args);
   ~~~~~~~^~~~~~~~~~~~~~~~~

Let get rid of them by adding -Wno-unused-result.

* cc: Fix comparison between signed and unsigned value

With llvm-7.0.0:

/home/lecopzer/workspace/bcc/src/cc/common.cc: In function ‘std::__cxx11::string ebpf::get_pid_exe(pid_t)’:
/home/lecopzer/workspace/bcc/src/cc/common.cc:60:11: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   if (res >= sizeof(exe_path))
       ~~~~^~~~~~~~~~

As the declaration of `exe_path` is `char exe_path[4096]`,
the `sizeof(exe_path)` would always return 4096 (unsigned), so it's safe
to static cast to `int` unless it's larger than 2^31 - 1.

* tools: Add shmsnoop to spy on shm* syscalls

Adding shmsnoop tool to trace System V shared memory
syscalls: shmget, shmat, shmdt, shmctl

  # ./shmsnoop.py
  PID    COMM                SYS              RET ARGs
  19813  server           SHMGET            10000 key: 0x78020001, size: 20, shmflg: 0x3b6 (IPC_CREAT|0666)
  19813  server            SHMAT     7f1cf8b1f000 shmid: 0x10000, shmaddr: 0x0, shmflg: 0x0
  19816  client           SHMGET            10000 key: 0x78020001, size: 20, shmflg: 0x1b6 (0666)
  19816  client            SHMAT     7f4fd8ee7000 shmid: 0x10000, shmaddr: 0x0, shmflg: 0x0
  19816  client            SHMDT                0 shmaddr: 0x7f4fd8ee7000
  19813  server            SHMDT                0 shmaddr: 0x7f1cf8b1f000
  19813  server           SHMCTL                0 shmid: 0x10000, cmd: 0, buf: 0x0

Every call the shm* syscall (SHM column) is displayed
on separate line together with process info (PID/COMM
columns) and argument details: return value (RET column)
and syscall arguments (ARGs column).

The ARGs column contains 'arg: value' couples that represent
given syscall arguments as described in their manpage.

It supports standard options to filter on pid/tid,
to specify duration of the trace and command name
filter, like:

    ./shmsnoop           # trace all shm*() syscalls
    ./shmsnoop -T        # include timestamps
    ./shmsnoop -p 181    # only trace PID 181
    ./shmsnoop -t 123    # only trace TID 123
    ./shmsnoop -d 10     # trace for 10 seconds only
    ./shmsnoop -n main   # only print process names containing "main"

* tools: Add sofdsnoop to spy on fds passed through socket

The sofdsnoop traces FDs passed through unix sockets.

  # ./sofdsnoop
  ACTION TID    COMM             SOCKET                    FD    NAME
  SEND   2576   Web Content      24:socket:[39763]         51    /dev/shm/org.mozilla.ipc.2576.23874
  RECV   2576   Web Content      49:socket:[809997]        51
  SEND   2576   Web Content      24:socket:[39763]         58    N/A
  RECV   2464   Gecko_IOThread   75:socket:[39753]         55

Every file descriptor that is passed via unix sockets os displayed
on separate line together with process info (TID/COMM columns),
ACTION details (SEND/RECV), file descriptor number (FD) and its
translation to file if available (NAME).

examples:
    ./sofdsnoop           # trace file descriptors passes
    ./sofdsnoop -T        # include timestamps
    ./sofdsnoop -p 181    # only trace PID 181
    ./sofdsnoop -t 123    # only trace TID 123
    ./sofdsnoop -d 10     # trace for 10 seconds only
    ./sofdsnoop -n main   # only print process names containing "main"

* inject: add option to limit number of overrides

* inject: update man pages with new count option
Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>

* add kernel stack trace option to capable
Signed-off-by: Andrea Righi <andrea@betterlinux.com>

* capable: avoid stack trace overwrite

Use 0 in get_stack() to avoid overwriting the stack trace in the
kernel for the same stack_id.
Signed-off-by: Andrea Righi <righi.andrea@gmail.com>

* capable: print both TID and PID
Signed-off-by: Andrea Righi <righi.andrea@gmail.com>

* add user-space stack trace option to capable
Signed-off-by: Andrea Righi <righi.andrea@gmail.com>

* capable: avoid catching itself
Signed-off-by: Andrea Righi <righi.andrea@gmail.com>

* capable: drop unused member pid_tgid in struct
Signed-off-by: Andrea Righi <righi.andrea@gmail.com>

* capable: report a proper error message when stack trace is missing

Print [Missed User Stack] or [Missed Kernel Stack] when get_stackid()
returns an error.
Signed-off-by: Andrea Righi <righi.andrea@gmail.com>

* capable: add missing errno import
Signed-off-by: Andrea Righi <righi.andrea@gmail.com>

* capable: remove dependency from python-enum module
Signed-off-by: Andrea Righi <righi.andrea@gmail.com>

This reorders the struct data_t members so that the definition
is consistent across the c code and the corresponding python
ct.Structure.

Upon running the script with the arguments option, the user and
kernel stack ids read from the stack maps are incorrect as they
are read off the wrong structure offsets. When a stack walk is
attempted on an incorrect stack id, we end up with a KeyError.

This has been verified as shown below.

  $ sudo ./funcslower.py c:inet_pton -u1 -a1 -UK
  $ ping -6 ::1

Before:
  Tracing function calls slower than 1 us... Ctrl+C to quit.
  COMM           PID    LAT(us)             RVAL FUNC ARGS
  ping           33541    47.93                1 c:inet_pton 0xfffffff2000001a0
  Traceback (most recent call last):
    File "_ctypes/callbacks.c", line 315, in 'calling callback function'
    File "/usr/lib/python2.7/site-packages/bcc/table.py", line 573, in raw_cb_
      callback(cpu, data, size)
    File "./funcslower.py", line 337, in print_event
      print_stack(event)
    File "./funcslower.py", line 301, in print_stack
      user_stack = stack_traces.walk(event.user_stack_id)
    File "/usr/lib/python2.7/site-packages/bcc/table.py", line 768, in walk
      return StackTrace.StackWalker(self[self.Key(stack_id)], resolve)
    File "/usr/lib/python2.7/site-packages/bcc/table.py", line 212, in __getitem__
      raise KeyError
  KeyError

After:
  Tracing function calls slower than 1 us... Ctrl+C to quit.
  COMM           PID    LAT(us)             RVAL FUNC ARGS
  ping           34672    48.20                1 c:inet_pton 0xa
      gaih_inet.constprop.7
      [unknown]
      getaddrinfo
      [unknown]
      generic_start_main.isra.0
      __libc_start_main

Fixes: 925bac87 ("Adding user and kernel stack frames option to funcslower")
Signed-off-by: Sandipan Das <sandipan@linux.ibm.com>

Fix issue #2035.

For code like
    int i;
    int j = 0;
    const int last_index = payload_offset + 7;
    for (i = payload_offset ; i < last_index ; i++) {
               p[j] = load_byte(skb , i);

Here, the payload_offset is unknown. llvm 7.0 and trunk
compiler seems generating code like
   p[0] = load_byte(skb, payload_offset)
   if (payload_offset + 1 < last_index) {
      p[1] = ...
      ...
      p[6] = ...
   } else {
      /* do nothing */
   }
   /* accessing p[0], p[1], ..., p[6] */

The compiler did the above transformation because the potential
overflow for last_index and/or payload_offset + 1 in which case
compiler preserved both branches.

This caused a problem for verifier as in the else branch
p[1] is not assigned and the verifier will reject the program.

Changing the loop to simply iterate from 0 to 6 fixed the problem.
Signed-off-by: Yonghong Song <yhs@fb.com>

install docs - on ubuntu bionic use llvm 6.0

* Use correct entry point for uprobes on powerpc64

For powerpc64 (big endian), the address of a function is the
address of the corresponding function descriptor. While the
actual functions reside in the ".text" section, the function
descriptors are present in the ".opd" section. According to
the ABI, each descriptor is a tri-doubleword data structure
where the first doubleword is the actual entry point address.

The symbol table entries do not list actual entry points but
instead provide the location of the function descriptor. So,
when attaching a probe, the location should be changed to the
actual entry point by peeking into the function descriptor.

This has been verified as shown below.

  $ readelf -S /usr/lib64/power8/libc-2.26.so | grep -A1 ".opd"
    [30] .opd              PROGBITS         0000000000213648  00203648
         000000000000bcb8  0000000000000000  WA       0     0     8

The first column shows the index of the ".opd" section.

  $ readelf -s /usr/lib64/power8/libc-2.26.so | grep "inet_pton$"
    3405: 000000000021d168    96 FUNC    LOCAL  DEFAULT   30 __inet_pton
    3990: 000000000021d168    96 FUNC    LOCAL  DEFAULT   30 __GI___inet_pton
    5167: 000000000021d168    96 FUNC    LOCAL  DEFAULT   30 __GI_inet_pton
    6514: 000000000021d168    96 FUNC    WEAK   DEFAULT   30 inet_pton

The seventh column shows the index of the section to which the
symbols belong. This implies that all of these symbols are from
the ".opd" section.

  $ objdump -d --section=.opd /usr/lib64/power8/libc-2.26.so | grep -A5 "inet_pton>:"
  000000000021d168 <inet_pton>:
    21d168:       00 00 00 00     .long 0x0
    21d16c:       00 17 2b 40     .long 0x172b40
    21d170:       00 00 00 00     .long 0x0
    21d174:       00 22 73 00     .long 0x227300

  $ objdump -d /usr/lib64/power8/libc-2.26.so | grep -A5 "inet_pton>:"
  0000000000172b40 <.__inet_pton>:
    172b40:       7c 08 02 a6     mflr    r0
    172b44:       fb c1 ff f0     std     r30,-16(r1)
    172b48:       fb e1 ff f8     std     r31,-8(r1)
    172b4c:       7c 7f 1b 78     mr      r31,r3
    172b50:       7c 83 23 78     mr      r3,r4

The first doubleword in the descriptor of "inet_pton" gives the
actual entry point address i.e. 0x172b40. So, the probe must be
attached here and not 0x21d168.

  $ sudo trace "c:inet_pton" -U
  PID     TID     COMM            FUNC
  40769   40769   ping            inet_pton
          __GI___inet_pton+0x0 [libc-2.26.so]
          gaih_inet.constprop.7+0xf4c [libc-2.26.so]
          __GI_getaddrinfo+0x15c [libc-2.26.so]
          [unknown] [ping]
          generic_start_main.isra.0+0x150 [libc-2.26.so]
          __libc_start_main+0xbc [libc-2.26.so]

  $ ping -6 ::1
  PING ::1(::1) 56 data bytes
  64 bytes from ::1: icmp_seq=1 ttl=64 time=0.271 ms
  64 bytes from ::1: icmp_seq=2 ttl=64 time=0.039 ms
  ^C
  --- ::1 ping statistics ---
  2 packets transmitted, 2 received, 0% packet loss, time 1058ms
  rtt min/avg/max/mdev = 0.039/0.155/0.271/0.116 ms

Previously, the event was not triggered upon running ping.
Signed-off-by: Sandipan Das <sandipan@linux.ibm.com>

* Use correct entry point for uprobes on powerpc64le

For powerpc64le, functions have a Global Entry Point (GEP)
and a Local Entry Point (LEP). When using the GEP, there
are some additional instructions at the beginning of the
function that setup the TOC pointer. However, for all local
calls, the TOC pointer is not required and a function can
be called into directly via the LEP.

While placing a uprobe, we should always prefer the LEP as
the probe location since this will be encountered for any
call through either the GEP or the LEP. Currently, the GEP
is used as the probe location and hence the corresponding
event is never triggered when the function is called via
it's LEP.

Information about the LEP can be obtained from the st_other
field of an Elf symbol. While this field typically provides
visibility information, the three most significant bits can
provide additional information about the offset of the Local
Entry Point (LEP) from the Global Entry Point (GEP) for any
symbol in case of powerpc64le.

This has been verified as shown below.

  $ readelf -s /usr/lib64/libc-2.27.so | grep "inet_pton "
  3522: 0000000000164610   104 FUNC    LOCAL  DEFAULT   11 __inet_pton  [<localentry>: 8]
  4188: 0000000000164610   104 FUNC    LOCAL  DEFAULT   11 __GI___inet_pton     [<localentry>: 8]
  5528: 0000000000164610   104 FUNC    LOCAL  DEFAULT   11 __GI_inet_pton       [<localentry>: 8]
  6925: 0000000000164610   104 FUNC    WEAK   DEFAULT   11 inet_pton    [<localentry>: 8]

  $ sudo trace "c:inet_pton" -U
  PID     TID     COMM            FUNC
  25383   25383   ping            inet_pton
          __GI___inet_pton+0x8 [libc-2.27.so]
          gaih_inet.constprop.7+0x1040 [libc-2.27.so]
          getaddrinfo+0x164 [libc-2.27.so]
          [unknown] [ping]
          generic_start_main.isra.0+0x138 [libc-2.27.so]
          __libc_start_main+0xc4 [libc-2.27.so]

  $ ping -6 ::1
  PING ::1(::1) 56 data bytes
  64 bytes from ::1: icmp_seq=1 ttl=64 time=0.140 ms
  64 bytes from ::1: icmp_seq=2 ttl=64 time=0.029 ms
  ^C
  --- ::1 ping statistics ---
  2 packets transmitted, 2 received, 0% packet loss, time 1022ms
  rtt min/avg/max/mdev = 0.029/0.084/0.140/0.056 ms

Previously, the event was not triggered upon running ping.
Signed-off-by: Sandipan Das <sandipan@linux.ibm.com>

Fix the lua standalone test

When kprobe/kreprobe/tracepoint attachment fails, print the name of the
failing function and its target.
Signed-off-by: Oriol Arcas <oriol@starflownetworks.com>

This fixes the subtest that checks if bcc-lua depends on
libluajit.
Signed-off-by: Sandipan Das <sandipan@linux.ibm.com>

Fix symbol resolution across mount namespaces (#2029)

This updates the python and lua bindings for libbcc to be
able to support attaching kprobes at custom offsets.
Signed-off-by: Sandipan Das <sandipan@linux.ibm.com>

docs: fix kernel versions for a few newly added helpers.

Fix parsing of /proc/pid/maps

* Coverity #def53: COPY_PASTE_ERROR

* Coverity #def18: DC.STREAM_BUFFER. Double-check max length of dev

* Coverity #def44: MISSING_BREAK. This looks like it should be here

* Coverity #def67: STRING_NULL: potential OOB read if 0 bytes read.

* Coverity #def66: FORWARD_NULL: potential null ptr deref

* Coverity #def17: RESOURCE_LEAK: missing free()

* Dont free the result of dirname

dirname() may return pointers to statically allocated memory. Don't
free the pointer it returns.

Fix USDT semaphore address calculation for position independent executables (resolves #1998) (#2023)

Fix USDT semaphore address calculation for position independent executables

Fix issue #2017.

For python programs, the map data passed from C++ library
is parsed through the key/value desc types which are
generated by C++ json map declaration visitor.

The map declaration visitor visits the map key/value
declaration types and generate a string to represent
the type, which is later used by python to reconstruct
the cttype.

The map declaration already tries to add all the padding
to the type string in order to make sure C++ and python
see the same layout.

This patch further added packed support such that if
C++ json map visitor has applied padding, the python
type reconstructor is free to add _pack_=1 for structure
type since the structure is already packed.

For example, for a type,
  struct t { char a; int b; }
the structure after json visitor will look like
  struct t { char a; char __pad[3]; int b; }

If the type is
  struct t { char a; int b; } __packed;
the structure after json visitor will look like
  struct t { char a; int b; }

In either case, it will be okay to add __packed attribute
for the type generated by json map visitor in order to
match the original declaration.

Thanks Chaitanya for filing the issue and providing the test case!
Signed-off-by: Yonghong Song <yhs@fb.com>

frontends: disable uint128_t on 32-bit builds

On 32-bit, __uint128_t is generally not available. Removing it fixes
builds on those systems.
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>