Commit Graph

398 Commits

Author SHA1 Message Date
Kevin Enderby 299cd890fe For llvm-objdump and Mach-O files, update the printing of some thread states
from core files.  I tested this against the couple of core files that were
getting errors about unknown thread flavors and it now produce the same output as
the Xcode otool-classic(1) tool.  Since the core files are huge I didn’t include
them as test cases.

rdar://38216356

llvm-svn: 327077
2018-03-08 23:10:38 +00:00
Michael Trent ca30902ff8 Do not look up symbol names when n_strx == 0
Summary:
Historical tools for working with mach-o binaries verify the nlist field
n_strx has a non-zero value before using that value to retrieve symbol names.
Under some cirumstances, llvm-nm will attempt to display the symbol name at 
position 0, even though symbol names at that position are not well defined. 
This change addresses this problem by returning an empty string when n_strx
is zero.

rdar://problem/35750548

Reviewers: enderby, davide

Reviewed By: enderby, davide

Subscribers: davide, llvm-commits, JDevlieghere

Differential Revision: https://reviews.llvm.org/D41657

llvm-svn: 321773
2018-01-03 23:28:32 +00:00
Michael Trent a1703b1fc2 Updated llvm-objdump to display local relocations in Mach-O binaries
Summary:
llvm-objdump's Mach-O parser was updated in r306037 to display external
relocations for MH_KEXT_BUNDLE file types. This change extends the Macho-O
parser to display local relocations for MH_PRELOAD files. When used with
the -macho option relocations will be displayed in a historical format.

All tests are passing for llvm, clang, and lld. llvm-objdump builds without
compiler warnings.

rdar://35778019

Reviewers: enderby

Reviewed By: enderby

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D41199

llvm-svn: 320832
2017-12-15 17:57:40 +00:00
Zachary Turner 260fe3eca6 Fix many -Wsign-compare and -Wtautological-constant-compare warnings.
Most of the -Wsign-compare warnings are due to the fact that
enums are signed by default in the MS ABI, while the
tautological comparison warnings trigger on x86 builds where
sizeof(size_t) is 4 bytes, so N > numeric_limits<unsigned>::max()
is always false.

Differential Revision: https://reviews.llvm.org/D41256

llvm-svn: 320750
2017-12-14 22:07:03 +00:00
Michael Trent 1d3d8adad7 reverting out -r320532 because a warning is breaking the lld build
llvm-svn: 320534
2017-12-13 00:36:13 +00:00
Michael Trent 0f6bfaf176 Updated llvm-objdump to display local relocations in Mach-O binaries
Summary:
llvm-objdump's Mach-O parser was updated in r306037 to display external
relocations for MH_KEXT_BUNDLE file types. This change extends the Macho-O
parser to display local relocations for MH_PRELOAD files. When used with
the -macho option relocations will be displayed in a historical format.

rdar://35778019

Reviewers: enderby

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D41061

llvm-svn: 320532
2017-12-12 23:53:46 +00:00
Michael Trent ad840d2206 Reverting r320166 to fix test failures.
llvm-svn: 320174
2017-12-08 19:09:26 +00:00
Michael Trent de5209bdbd Updated llvm-objdump to display local relocations in Mach-O binaries
Summary:
llvm-objdump's Mach-O parser was updated in r306037 to display external
relocations for MH_KEXT_BUNDLE file types. This change extends the Macho-O
parser to display local relocations for MH_PRELOAD files. When used with
the -macho option relocations will be displayed in a historical format.

rdar://35778019

Reviewers: enderby

Reviewed By: enderby

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D40867

llvm-svn: 320166
2017-12-08 17:51:04 +00:00
NAKAMURA Takumi 6f43bd4bde Untabify.
llvm-svn: 316079
2017-10-18 13:31:28 +00:00
Jessica Paquette 1a81dfba97 Fix typo in checkTwoLevelHintsCommand
BigSize had a copy/paste typo in it. This fixes that.

llvm-svn: 316027
2017-10-17 20:43:33 +00:00
Jonas Devlieghere 8af2387b91 [dwarfdump] Skip 'stripped' sections
When dsymutil generates the companion file, its strips all unnecessary
sections by omitting their body and setting the offset in their
corresponding load command to zero.

One such section is the .eh_frame section, as it contains runtime
information rather than debug information and is part of the __TEXT
segment. When reading this section, we would just read the number of
bytes specified in the load command, starting from offset 0 (i.e. the
beginning of the file).

Rather than trying to parse this obviously invalid section, dwarfdump
now skips this.

Differential revision: https://reviews.llvm.org/D38135

llvm-svn: 314208
2017-09-26 14:22:35 +00:00
Jonas Devlieghere 81f5abe1ad [MachO] Prevent heap overflow when load command extends past EOF
This patch fixes a heap-buffer-overflow when a malformed Mach-O has a
load command who's size extends past the end of the binary.

Fixes: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=3225

Differential revision: https://reviews.llvm.org/D37439

llvm-svn: 313145
2017-09-13 13:43:01 +00:00
NAKAMURA Takumi a1e97a77f5 Untabify.
llvm-svn: 311875
2017-08-28 06:47:47 +00:00
Benjamin Kramer 760e00b0bc [MachO] Use Twines more efficiently.
llvm-svn: 311291
2017-08-20 15:13:39 +00:00
Alexander Shaposhnikov e574034f28 [llvm] Update MachOObjectFile::exports interface
This diff removes the second argument of the method MachOObjectFile::exports.
In all in-tree uses this argument is equal to "this" and 
without this argument the interface seems to be cleaner.

Test plan: make check-all

llvm-svn: 309462
2017-07-29 00:30:45 +00:00
Kevin Enderby 8100cdeddf Small tweak to one check in error handling to the dyld compact export
entries in libObject (done in r308690).  In the case when the last node
has no children setting State.Current = Children + 1; where that would be past
Trie.end() is actually ok since the pointer is not used with zero children.

rdar://33490512

llvm-svn: 308924
2017-07-24 20:33:41 +00:00
Kevin Enderby 3e95bd2239 Add error handling to the dyld compact export entries in libObject.
lld needs a matching change for this will be my next commit.
Expect it to fail build until that matching commit is picked up by the bots.

Like the changes in r296527 for dyld bind entires and the changes in
r298883 for lazy bind, weak bind and rebase entries the export
entries are the last of the dyld compact info to have error handling added.

This follows the model of iterators that can fail that Lang Hanes
designed when fixing the problem for bad archives r275316 (or r275361).

So that iterating through the exports now terminates if there is an error
and returns an llvm::Error with an error message in all cases for malformed
input.

This change provides the plumbing for the error handling, all the needed
testing of error conditions and test cases for all of the unique error messages.

llvm-svn: 308690
2017-07-20 23:08:41 +00:00
Kevin Enderby abf10f2d2e Updated llvm-objdump symbolic disassembly with x86_64 Mach-O MH_KEXT_BUNDLE
file types so it symbolically disassembles operands using the external
relocation entries.

rdar://31521343

llvm-svn: 306037
2017-06-22 17:41:22 +00:00
Zachary Turner 264b5d9e88 Move Object format code to lib/BinaryFormat.
This creates a new library called BinaryFormat that has all of
the headers from llvm/Support containing structure and layout
definitions for various types of binary formats like dwarf, coff,
elf, etc as well as the code for identifying a file from its
magic.

Differential Revision: https://reviews.llvm.org/D33843

llvm-svn: 304864
2017-06-07 03:48:56 +00:00
Chandler Carruth 6bda14b313 Sort the remaining #include lines in include/... and lib/....
I did this a long time ago with a janky python script, but now
clang-format has built-in support for this. I fed clang-format every
line with a #include and let it re-sort things according to the precise
LLVM rules for include ordering baked into clang-format these days.

I've reverted a number of files where the results of sorting includes
isn't healthy. Either places where we have legacy code relying on
particular include ordering (where possible, I'll fix these separately)
or where we have particular formatting around #include lines that
I didn't want to disturb in this patch.

This patch is *entirely* mechanical. If you get merge conflicts or
anything, just ignore the changes in this patch and run clang-format
over your #include lines in the files.

Sorry for any noise here, but it is important to keep these things
stable. I was seeing an increasing number of patches with irrelevant
re-ordering of #include lines because clang-format was used. This patch
at least isolates that churn, makes it easy to skip when resolving
conflicts, and gets us to a clean baseline (again).

llvm-svn: 304787
2017-06-06 11:49:48 +00:00
Wolfgang Pieb 77d3e938f8 [DWARF] Adding support for the DWARF v5 string offsets table (consumer/reader part only).
Reviewers: dblaikie, aprantl

Differential Revision: https://reviews.llvm.org/D32779

llvm-svn: 304759
2017-06-06 01:22:34 +00:00
Steven Wu 97e2cf87e1 [MachOObject] Fix bind opcode parser error on valid opcode sequence
BIND_OPCODE_SET_DYLIB_SPECIAL_IMM(0) is a valid way to setp library
ordinal. MachOObject should set LibraryOrdinalSet even when IMM is zero.

llvm-svn: 304362
2017-05-31 22:17:43 +00:00
George Rimar a25d329b33 Recommit "[DWARF] - Make collectAddressRanges() return section index in addition to Low/High PC"
With fix of uninitialized variable.

Original commit message:

This change is intended to use for LLD in D33183. 
Problem we have in LLD when building .gdb_index is that we need to know section which address range belongs to.

Previously it was solved on LLD side by providing fake section addresses with use of llvm::LoadedObjectInfo
interface. We assigned file offsets as addressed. Then after obtaining ranges lists, for each range we had to find section ID's.
That not only was slow, but also complicated implementation and was the reason of incorrect behavior when
sections share the same offsets, like D33176 shows.

This patch makes DWARF parsers to return section index as well. That solves problem mentioned above.

Differential revision: https://reviews.llvm.org/D33184

llvm-svn: 304078
2017-05-27 18:10:23 +00:00
George Rimar 1f9cab6b1c Revert r304002 "[DWARF] - Make collectAddressRanges() return section index in addition to Low/High PC"
Revert it again. Now another bot unhappy: http://lab.llvm.org:8011/builders/clang-s390x-linux/builds/8750

llvm-svn: 304011
2017-05-26 17:36:23 +00:00
George Rimar bc223c63cc [DWARF] - Make collectAddressRanges() return section index in addition to Low/High PC
This change is intended to use for LLD in D33183. 
Problem we have in LLD when building .gdb_index is that we need to know section which address range belongs to.

Previously it was solved on LLD side by providing fake section addresses with use of llvm::LoadedObjectInfo
interface. We assigned file offsets as addressed. Then after obtaining ranges lists, for each range we had to find section ID's.
That not only was slow, but also complicated implementation and was the reason of incorrect behavior when
sections share the same offsets, like D33176 shows.

This patch makes DWARF parsers to return section index as well. That solves problem mentioned above.

Differential revision: https://reviews.llvm.org/D33184

llvm-svn: 304002
2017-05-26 16:26:18 +00:00
George Rimar a8403a64ea Revert "[DWARF] - Make collectAddressRanges() return section index in addition to Low/High PC"
Broked BB again:

TEST 'LLVM :: DebugInfo/X86/dbg-value-regmask-clobber.ll' FAILED
...
LLVM ERROR: Section was outside of section table.

llvm-svn: 303984
2017-05-26 13:20:09 +00:00
George Rimar 655b7b63f6 Recommit r303978 "[DWARF] - Make collectAddressRanges() return section index in addition to Low/High PC"
With fix of test compilation.

Initial commit message:

This change is intended to use for LLD in D33183. 
Problem we have in LLD when building .gdb_index is that we need to know section 
which address range belongs to.

Previously it was solved on LLD side by providing fake section addresses
with use of llvm::LoadedObjectInfo interface. We assigned file offsets as addressed.
Then after obtaining ranges lists, for each range we had to find section ID's.
That not only was slow, but also complicated implementation and was the reason 
of incorrect behavior when
sections share the same offsets, like D33176 shows.

This patch makes DWARF parsers to return section index as well. 
That solves problem mentioned above.

Differential revision: https://reviews.llvm.org/D33184

llvm-svn: 303983
2017-05-26 13:13:50 +00:00
George Rimar 7d5f12185a Revert r303978 "[DWARF] - Make collectAddressRanges() return section index in addition to Low/High PC"
It failed BB.

llvm-svn: 303981
2017-05-26 12:53:41 +00:00
George Rimar 732f268aa0 [DWARF] - Make collectAddressRanges() return section index in addition to Low/High PC
This change is intended to use for LLD in D33183. 
Problem we have in LLD when building .gdb_index is that we need to know section 
which address range belongs to.

Previously it was solved on LLD side by providing fake section addresses
with use of llvm::LoadedObjectInfo interface. We assigned file offsets as addressed.
Then after obtaining ranges lists, for each range we had to find section ID's.
That not only was slow, but also complicated implementation and was the reason 
of incorrect behavior when
sections share the same offsets, like D33176 shows.

This patch makes DWARF parsers to return section index as well. 
That solves problem mentioned above.

Differential revision: https://reviews.llvm.org/D33184

llvm-svn: 303978
2017-05-26 12:46:41 +00:00
Eugene Zelenko 9f5094df36 [Object] Fix some Clang-tidy modernize and Include What You Use warnings; other minor fixes (NFC).
llvm-svn: 301049
2017-04-21 22:03:05 +00:00
Vassil Vassilev e1f12fadc0 Remove unused functions. Remove static qualifier from functions in header files. NFC.
llvm-svn: 299947
2017-04-11 14:55:32 +00:00
Juergen Ributzka cad1249106 [Object] Remove check for BIND_OPCODE_DONE/REBASE_OPCODE_DONE.
BIND_OPCODE_DONE/REBASE_OPCODE_DONE may appear at the end of the opcode array,
but they are not required to. The linker only adds them as padding to align the
opcodes to pointer size.

This fixes rdar://problem/31285560.

llvm-svn: 299104
2017-03-30 19:56:50 +00:00
Kevin Enderby 6c1d2b4cb2 Add the error handling for Mach-O dyld compact lazy bind, weak bind and
rebase entry errors and test cases for each of the error checks.

Also verified with Nick Kledzik that a BIND_OPCODE_SET_ADDEND_SLEB
opcode is legal in a lazy bind table, so code that had that as an error
check was removed.

With MachORebaseEntry and MachOBindEntry classes now returning
an llvm::Error in all cases for malformed input the variables Malformed
and logic to set use them is no longer needed and has been removed
from those classes.

Also in a few places, removed the redundant Done assignment to true
when also calling moveToEnd() as it does that assignment.

This only leaves the dyld compact export entries left to have
error handling yet to be added for the dyld compact info.

llvm-svn: 298883
2017-03-27 20:09:23 +00:00
Kevin Enderby a8d256cb36 Add the rest of the error checking for Mach-O dyld compact bind entry errors
and test cases for each of the error checks.

To do this more plumbing was needed so that the segment indexes and
segment offsets can be checked.  Basically what was done was the SegInfo
from llvm-objdump’s MachODump.cpp was moved into libObject for Mach-O
objects as BindRebaseSegInfo and it is only created when an iterator for
bind or rebase entries are created.

This commit really only adds the error checking and test cases for the
bind table entires and the checking for the lazy bind and weak bind entries
are still to be fully done as well as the rebase entires.  Though some of
the plumbing for those are added with this commit.  Those other error
checks and test cases will be added in follow on commits.

Note, the two llvm_unreachable() calls should now actually be unreachable
with the error checks in place and would take a logic bug in the error
checking code to be reached if the segment indexes and segment
offsets are used from a checked bind entry.  Comments have been added
to the methods that require the arguments to have been checked
prior to calling.

llvm-svn: 298292
2017-03-20 19:46:55 +00:00
Kevin Enderby feb63b9391 Actually add error handling to unpacking the dyld compact bind and
other tables.  Providing a helpful error message to what the error is and
where the error occurred based on which opcode it was associated with.

There have been handful of bug fixes dealing with bad bind info in
object files, r294021 and r249845, which only put a band aid on the
problem after a bad bind table was created after unpacking from
its compact info.  In these cases a bind table should have never been
created and an error should have simply been generated.

This change puts in place the plumbing to allow checking and returning
of an error when the compact info is unpacked.  This follows the model
of iterators that can fail that Lang Hanes designed when fixing the problem
for bad archives r275316 (or r275361).

This change uses one of the existing test cases that now causes an
error instead of printing <<bad library ordinal>> after a bad bind table
is created.  The error uses the offset into the opcode table as shown with
the macOS dyldinfo(1) tool to indicate where the error is and which
opcode and which parameter is in error.

For example the exiting test case has this lazy binding opcode table:

% dyldinfo -opcodes test/tools/llvm-objdump/Inputs/bad-ordinal.macho-x86_64 
…
lazy binding opcodes:
0x0000 BIND_OPCODE_SET_SEGMENT_AND_OFFSET_ULEB(0x02, 0x00000010)
0x0002 BIND_OPCODE_SET_DYLIB_ORDINAL_IMM(2)

In the test case the binary only has one library so setting the library 
ordinal to the value of 2 in the BIND_OPCODE_SET_DYLIB_ORDINAL_IMM
opcode at 0x0002 above is an error.  This now produces this error message:

% llvm-objdump -lazy-bind bad-ordinal.macho-x86_64 
…
llvm-objdump: 'bad-ordinal.macho-x86_64': truncated or malformed object (for BIND_OPCODE_SET_DYLIB_ORDINAL_ULEB bad library ordinal: 2 (max 1) for opcode at: 0x2)

This change provides the plumbing for the error handling and one example
of an error message.  Other error checks and test cases will be added in follow
on commits.

llvm-svn: 296527
2017-02-28 21:47:07 +00:00
Kevin Enderby dc412ccc41 Yet another fix llvm-objdump so it picks a good CPU based for Mach-O files,
in this case for CPU_SUBTYPE_ARM64_ALL.

For this cpusubtype it should default to a cyclone CPU
to give proper disassembly without a -mcpu= flag.

rdar://27767188

llvm-svn: 294771
2017-02-10 19:27:10 +00:00
Kevin Enderby 86d8bd1da5 Fix a typo in an error message for a check of invalid Mach-O files where
it was printing the field name fileoff instead of filesize.  The original check
was added in r278557.

This was found in tracking down the problem that lead to the fix in
r293842 - [dsymutil] Fix __LINKEDIT vmsize in dsymutil upgrade path

rdar://30386075

llvm-svn: 294354
2017-02-07 21:20:44 +00:00
Kevin Enderby 7a165755ba Fix llvm-objdump so it picks a good CPU based for Mach-O files
for CPU_SUBTYPE_ARM_V7S and CPU_SUBTYPE_ARM_V7K.

For these two cpusubtypes they should default to a cortex-a7 CPU
to give proper disassembly without a -mcpu= flag.

rdar://27431703

llvm-svn: 292993
2017-01-24 23:41:04 +00:00
Kevin Enderby c3a035d86f Add support for the x86_thread_state32_t and
in llvm-objdump for Mach-O files add the printing of the
x86_thread_state32_t in the same format as
otool-classic(1) on darwin.

To do this the 32-bit x86 general tread state
needed to be defined in include/llvm/Support/MachO.h .

rdar://30110111

llvm-svn: 292829
2017-01-23 21:13:29 +00:00
Steven Wu 5b54a42c0f Add LC_BUILD_VERSION load command
Summary:
Add a new load command LC_BUILD_VERSION. It is a generic version of
LC_*_VERSION_MIN load_command used on Apple platforms. Instead of having
a seperate load command for each platform, LC_BUILD_VERSION is recording
platform info as an enum. It also records SDK version, min_os, and tools
that used to build the binary.

rdar://problem/29781291

Reviewers: enderby

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D29044

llvm-svn: 292824
2017-01-23 20:07:55 +00:00
Kevin Enderby a4579c4184 Add support for the new LC_NOTE load command.
It describes a region of arbitrary data included in a Mach-O file.
Its initial use is to record extra data in MH_CORE files.

rdar://30001545
rdar://30001731

llvm-svn: 292500
2017-01-19 17:36:31 +00:00
Saleem Abdulrasool 1d84d9ac48 llvm-objdump: speed up -objc-meta-data
Running a Debug build of objdump -objc-meta-data with a large Mach-O file is
currently unnecessarily slow.

With some local test input, this change reduces the run time from 75-85s down
to 15-20s.

The two changes are:
  Assert on pointer equality not array equality
  Replace vector<pair<address, symbol>> with DenseMap<address, symbol>

Additionally, use a std::unique_ptr rather than handling the memory manually.

Patch by Dave Lee!

llvm-svn: 291398
2017-01-08 19:14:15 +00:00
Kevin Enderby 59343a9429 Fix a bugs with using some Mach-O command line flags like "-arch armv7m".
The Mach-O command line flag like "-arch armv7m" does not match the
arch name part of its llvm Triple which is "thumbv7m-apple-darwin”.

I think the best way to fix this is to have
llvm::object::MachOObjectFile::getArchTriple() optionally return the
name of the Mach-O arch flag that would be used with -arch that
matches the CPUType and CPUSubType.  Then change
llvm::object::MachOUniversalBinary::ObjectForArch::getArchTypeName()
to use that and change it to getArchFlagName() as the type name is
really part of the Triple and the -arch flag name is a Mach-O thing
for a specific Triple with a specific Mcpu value.

rdar://29663637

llvm-svn: 290001
2016-12-16 22:54:02 +00:00
Lang Hames 697e7cd761 [Object][MachO] Reference-ify some helper function arguments. NFC.
Changes all static helper functions in MachOObjectFile.cpp that expect a
non-null MachOObjectFile pointer to take a reference instead.

llvm-svn: 288608
2016-12-04 01:56:10 +00:00
Peter Collingbourne 435890a4fe Object: Make SymbolicFile::symbol_{begin,end}() virtual and remove unnecessary wrappers.
llvm-svn: 287611
2016-11-22 03:38:40 +00:00
Kevin Enderby 22fc007809 Add a checkSymbolTable() method to the MachOObjectFile class.
The philosophy of the error checking in libObject for Mach-O files
is that the constructor will check the load commands so for their
tables the offsets and sizes are properly contained in the file.
But there is no checking of the entries of any of the tables.

For the contents of the tables themselves the methods accessing
the contents of the entries return errors as needed.  In some
cases this however makes it difficult or cumbersome to produce
a good error message which would include the tool name, file name,
archive member, and name of the architecture of a slice of a universal file
the error occurred in.

So idea is that there will be a method to check a table which can
be called up front before using it allowing a good error message
to be produced before a table is used.  And if only verification of
the Mach-O file and its tables are wanted a new possible method
checkAllTables() could be added to call all of the methods to
check all the tables at some time when such methods exist.

The checkSymbolTable() is the first of such methods to check
one of the Mach-O file tables.  This method initially will used in
llvm-objdump’s DisassembleMachO() routine before it gets the
section and symbol information.  As if there are problems with
the symbol table currently the error is first encountered by the
bool operator() in the SymbolSorter() struct which passed to
std::sort().  In this case there is no context as to the file name
the symbol which results a poor error message:

LLVM ERROR: truncated or malformed object (bad string index: 22 for symbol at index 1)

with the added call to the checkSymbolTable() method the
error message includes the tool name and file name:

llvm-objdump: 'macho-invalid-symbol-strx': truncated or malformed object (bad string table index: 22 past the end of string table, for symbol at index 1)
llvm-svn: 286887
2016-11-14 20:57:04 +00:00
Mehdi Amini 41af43092c Make the Error class constructor protected
This is forcing to use Error::success(), which is in a wide majority
of cases a lot more readable.

Differential Revision: https://reviews.llvm.org/D26481

llvm-svn: 286561
2016-11-11 04:28:40 +00:00
Kevin Enderby 7747cb55dc Add support for the ARM_THREAD_STATE64 and
in llvm-objdump for Mach-O files add the printing of the
ARM_THREAD_STATE64 in the same format as
otool-classic(1) on darwin.

To do this the 64-bit ARM general tread state
needed to be defined in include/llvm/Support/MachO.h .

rdar://28985800

llvm-svn: 285967
2016-11-03 20:51:28 +00:00
Kevin Enderby fbebe1632a Add the rest of the additional error checks for invalid Mach-O files when
the offsets and sizes of an element of the Mach-O file overlaps with
another element in the Mach-O file.

Some other tests for malformed Mach-O files now run into these
checks so their tests were also adjusted.

llvm-svn: 285860
2016-11-02 21:08:39 +00:00
Kevin Enderby d503940e8f More additional error checks for invalid Mach-O files when
the offsets and sizes of an element of the file overlaps with
another element in the Mach-O file.

This shows the approach to this testing for three elements
and contains for tests for their overlap.  Checking for all the
remain elements will be added next.

llvm-svn: 285632
2016-10-31 20:29:48 +00:00