Introduce a DW_OP_LLVM_convert Dwarf expression pseudo op that allows
for a convenient way to perform type conversions on the Dwarf expression
stack. As an additional bonus it paves the way for using other Dwarf
v5 ops that need to reference a base_type.
The new DW_OP_LLVM_convert is used from lib/Transforms/Utils/Local.cpp
to perform sext/zext on debug values but mainly the patch is about
preparing terrain for adding other Dwarf v5 ops that need to reference a
base_type.
For Dwarf v5 the op maps to DW_OP_convert and for earlier versions a
complex shift & mask pattern is generated to emulate sext/zext.
Differential Revision: https://reviews.llvm.org/D56587
llvm-svn: 356442
Summary: Initial function labels must follow the debug location for the correct relocation info generation.
Reviewers: tra, jlebar, echristo
Subscribers: jholewinski, llvm-commits
Differential Revision: https://reviews.llvm.org/D45784
llvm-svn: 351843
to reflect the new license.
We understand that people may be surprised that we're moving the header
entirely to discuss the new license. We checked this carefully with the
Foundation's lawyer and we believe this is the correct approach.
Essentially, all code in the project is now made available by the LLVM
project under our new license, so you will see that the license headers
include that license only. Some of our contributors have contributed
code under our old license, and accordingly, we have retained a copy of
our old license notice in the top-level files in each project and
repository.
llvm-svn: 351636
This patch moved the following files in lib/CodeGen/AsmPrinter/
AsmPrinterHandler.h
DbgEntityHistoryCalculator.h
DebugHandlerBase.h
to include/llvm/CodeGen directory.
Such a change will enable Target to extend DebugHandlerBase
and emit Target specific debug info sections.
Signed-off-by: Yonghong Song <yhs@fb.com>
Differential Revision: https://reviews.llvm.org/D55755
llvm-svn: 349564
In ThinLTO many split CUs may be effectively empty because of the lack
of support for cross-unit references in split DWARF.
Using a split unit in those cases is just a waste/overhead - and turned
out to be one contributor to a significant symbolizer performance issue
when global variable debug info was being imported (see r348416 for the
primary fix) due to symbolizers seeing CUs with no ranges, assuming
there might still be addresses covered and walking into the split CU to
see if there are any ranges (when that split CU was in a DWP file, that
meant loading the DWP and its index, the index was extra large because
of all these fractured/empty CUs... and so was very expensive to load).
(the 3rd fix which will follow, is to assume that a CU with no ranges is
empty rather than merely missing its CU level range data - and to not
walk into its DIEs (split or otherwise) in search of address information
that is generally not present)
llvm-svn: 349207
This makes the offsets larger (since they are further from the base
address) but those are in the .dwo - and allows removing addresses and
relocations from the .o file.
This could be built into the AddressPool more fundamentally, perhaps -
when you ask for an AddressPool entry you could say "or give me some
other entry and an offset I need to use" - though what to do about
situations where the first use of an address in a section is not the
earliest address in that section... is tricky.
At least with range addresses we can be fairly sure we've seen the
earliest address first because we see the start address for the
function.
llvm-svn: 345224
The initial patch was not reviewed, and does not have any tests;
it should not have been merged.
This reverts 344395, 344390, 344387, 344385, 344381, 344376,
and 344366.
llvm-svn: 344405
BTF is the debug format for BPF, a kernel virtual machine
and widely used for tracing, networking and security, etc ([1]).
Currently only instruction streams are passed to kernel,
the kernel verifier verifies them before execution. In order to
provide better visibility of bpf programs to user space
tools, some debug information, e.g., function names and
debug line information are desirable for kernel so tools
can get such information with better annotation
for jited instructions for performance or other reasons.
The dwarf is too complicated in kernel and for BPF.
Hence, BTF is designed to be the debug format for BPF ([2]).
Right now, pahole supports BTF for types, which
are generated based on dwarf sections in the ELF file.
In order to annotate performance metrics for jited bpf insns,
it is necessary to pass debug line info to the kernel.
Furthermore, we want to pass the actual code to the
kernel because of the following reasons:
. bpf program typically is small so storage overhead
should be small.
. in bpf land, it is totally possible that
an application loads the bpf program into the
kernel and then that application quits, so
holding debug info by the user space application
is not practical.
. having source codes directly kept by kernel
would ease deployment since the original source
code does not need ship on every hosts and
kernel-devel package does not need to be
deployed even if kernel headers are used.
The only reliable time to get the source code is
during compilation time. This will result in both more
accurate information and easier deployment as
stated in the above.
Another consideration is for JIT. The project like bcc
use MCJIT to compile a C program into bpf insns and
load them to the kernel ([3]). The generated BTF sections
will be readily available for such cases as well.
This patch implemented generation of BTF info in llvm
compiler. The BTF related sections will be generated
when both -target bpf and -g are specified. Two sections
are generated:
.BTF contains all the type and string information, and
.BTF.ext contains the func_info and line_info.
The separation is related to how two sections are used
differently in bpf loader, e.g., linux libbpf ([4]).
The .BTF section can be loaded into the kernel directly
while .BTF.ext needs loader manipulation before loading
to the kernel. The format of the each section is roughly
defined in llvm:include/llvm/MC/MCBTFContext.h and
from the implementation in llvm:lib/MC/MCBTFContext.cpp.
A later example also shows the contents in each section.
The type and func_info are gathered during CodeGen/AsmPrinter
by traversing dwarf debug_info. The line_info is
gathered in MCObjectStreamer before writing to
the object file. After all the information is gathered,
the two sections are emitted in MCObjectStreamer::finishImpl.
With cmake CMAKE_BUILD_TYPE=Debug, the compiler can
dump out all the tables except insn offset, which
will be resolved later as relocation records.
The debug type "btf" is used for BTFContext dump.
Dwarf tests the debug info generation with
llvm-dwarfdump to decode the binary sections and
check whether the result is expected. Currently
we do not have such a tool yet. We will implement
btf dump functionality in bpftool ([5]) as the bpftool is
considered the recommended tool for bpf introspection.
The implementation for type and func_info is tested
with linux kernel test cases. The line_info is visually
checked with dump from linux kernel libbpf ([4]) and
checked with readelf dumping section raw data.
Note that the .BTF and .BTF.ext information will not
be emitted to assembly code and there is no assembler
support for BTF either.
In the below, with a clang/llvm built with CMAKE_BUILD_TYPE=Debug,
Each table contents are shown for a simple C program.
-bash-4.2$ cat -n test.c
1 struct A {
2 int a;
3 char b;
4 };
5
6 int test(struct A *t) {
7 return t->a;
8 }
-bash-4.2$ clang -O2 -target bpf -g -mllvm -debug-only=btf -c test.c
Type Table:
[1] FUNC name_off=1 info=0x0c000001 size/type=2
param_type=3
[2] INT name_off=12 info=0x01000000 size/type=4
desc=0x01000020
[3] PTR name_off=0 info=0x02000000 size/type=4
[4] STRUCT name_off=16 info=0x04000002 size/type=8
name_off=18 type=2 bit_offset=0
name_off=20 type=5 bit_offset=32
[5] INT name_off=22 info=0x01000000 size/type=1
desc=0x02000008
String Table:
0 :
1 : test
6 : .text
12 : int
16 : A
18 : a
20 : b
22 : char
27 : test.c
34 : int test(struct A *t) {
58 : return t->a;
FuncInfo Table:
sec_name_off=6
insn_offset=<Omitted> type_id=1
LineInfo Table:
sec_name_off=6
insn_offset=<Omitted> file_name_off=27 line_off=34 line_num=6 column_num=0
insn_offset=<Omitted> file_name_off=27 line_off=58 line_num=7 column_num=3
-bash-4.2$ readelf -S test.o
......
[12] .BTF PROGBITS 0000000000000000 0000028d
00000000000000c1 0000000000000000 0 0 1
[13] .BTF.ext PROGBITS 0000000000000000 0000034e
0000000000000050 0000000000000000 0 0 1
[14] .rel.BTF.ext REL 0000000000000000 00000648
0000000000000030 0000000000000010 16 13 8
......
-bash-4.2$
The latest linux kernel ([6]) can already support .BTF with type information.
The [7] has the reference implementation in linux kernel side
to support .BTF.ext func_info. The .BTF.ext line_info support is not
implemented yet. If you have difficulty accessing [6], you can
manually do the following to access the code:
git clone https://github.com/yonghong-song/bpf-next-linux.git
cd bpf-next-linux
git checkout btf
The change will push to linux kernel soon once this patch is landed.
References:
[1]. https://www.kernel.org/doc/Documentation/networking/filter.txt
[2]. https://lwn.net/Articles/750695/
[3]. https://github.com/iovisor/bcc
[4]. https://github.com/torvalds/linux/tree/master/tools/lib/bpf
[5]. https://github.com/torvalds/linux/tree/master/tools/bpf/bpftool
[6]. https://github.com/torvalds/linux
[7]. https://github.com/yonghong-song/bpf-next-linux/tree/btf
Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Yonghong Song <yhs@fb.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Differential Revision: https://reviews.llvm.org/D52950
llvm-svn: 344366
It originally triggered a stepping problem in the debugger, which could
be fixed by adjusting CodeGen/LexicalScopes.cpp however it seems we prefer
the previous behavior anyway.
See the discussion for details: http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20181008/593833.html
This reverts commit r343880.
This reverts commit r343874.
llvm-svn: 344318
DWARF v5 introduces DW_AT_call_all_calls, a subprogram attribute which
indicates that all calls (both regular and tail) within the subprogram
have call site entries. The information within these call site entries
can be used by a debugger to populate backtraces with synthetic tail
call frames.
Tail calling frames go missing in backtraces because the frame of the
caller is reused by the callee. Call site entries allow a debugger to
reconstruct a sequence of (tail) calls which led from one function to
another. This improves backtrace quality. There are limitations: tail
recursion isn't handled, variables within synthetic frames may not
survive to be inspected, etc. This approach is not novel, see:
https://gcc.gnu.org/wiki/summit2010?action=AttachFile&do=get&target=jelinek.pdf
This patch adds an IR-level flag (DIFlagAllCallsDescribed) which lowers
to DW_AT_call_all_calls. It adds the minimal amount of DWARF generation
support needed to emit standards-compliant call site entries. For easier
deployment, when the debugger tuning is LLDB, the DWARF requirement is
adjusted to v4.
Testing: Apart from check-{llvm, clang}, I built a stage2 RelWithDebInfo
clang binary. Its dSYM passed verification and grew by 1.4% compared to
the baseline. 151,879 call site entries were added.
rdar://42001377
Differential Revision: https://reviews.llvm.org/D49887
llvm-svn: 343883
Context: Compiler generated instructions do not have a debug location
assigned to them. However emitting 0-line records for all of them bloats
the line tables for very little benefit so we usually avoid doing that.
Not emitting anything will lead to the previous debug location getting
applied to the locationless instructions. This is not desirable for
block begin and after labels. Previously we would emit simply emit
line-0 records in this case, this patch changes the behavior to do a
forward search for a debug location in these cases before emitting a
line-0 record to further reduce line table bloat.
Inspired by the discussion in https://reviews.llvm.org/D52862
llvm-svn: 343874
In DwarfDebug::collectEntityInfo(), if the label entity is processed in
DbgLabels list, it means the label is not optimized out. There is no
need to generate debug info for it with null position.
llvm-svn: 341513
There are two forms for label debug information in DWARF format.
1. Labels in a non-inlined function:
DW_TAG_label
DW_AT_name
DW_AT_decl_file
DW_AT_decl_line
DW_AT_low_pc
2. Labels in an inlined function:
DW_TAG_label
DW_AT_abstract_origin
DW_AT_low_pc
We will collect label information from DBG_LABEL. Before every DBG_LABEL,
we will generate a temporary symbol to denote the location of the label.
The symbol could be used to get DW_AT_low_pc afterwards. So, we create a
mapping between 'inlined label' and DBG_LABEL MachineInstr in DebugHandlerBase.
The DBG_LABEL in the mapping is used to query the symbol before it.
The AbstractLabels in DwarfCompileUnit is used to process labels in inlined
functions.
We also keep a mapping between scope and labels in DwarfFile to help to
generate correct tree structure of DIEs.
It also generates label debug information under global isel.
Differential Revision: https://reviews.llvm.org/D45556
llvm-svn: 340039
In cases where the debugger load time is a worthwhile tradeoff (or less
costly - such as loading from a DWP instead of a variety of DWOs
(possibly over a high-latency/distributed filesystem)) against object
file size, it can be reasonable to disable pubnames and corresponding
gdb-index creation in the linker.
A backend-flag version of this was implemented for NVPTX in
D44385/r327994 - which was fine for NVPTX which wouldn't mix-and-match
CUs. Now that it's going to be a user-facing option (likely powered by
"-gno-pubnames", the same as GCC) it should be encoded in the
DICompileUnit so it can vary per-CU.
After this, likely the NVPTX support should be migrated to the metadata
& the previous flag implementation should be removed.
Reviewers: aprantl
Differential Revision: https://reviews.llvm.org/D50213
llvm-svn: 339939
There are two forms for label debug information in DWARF format.
1. Labels in a non-inlined function:
DW_TAG_label
DW_AT_name
DW_AT_decl_file
DW_AT_decl_line
DW_AT_low_pc
2. Labels in an inlined function:
DW_TAG_label
DW_AT_abstract_origin
DW_AT_low_pc
We will collect label information from DBG_LABEL. Before every DBG_LABEL,
we will generate a temporary symbol to denote the location of the label.
The symbol could be used to get DW_AT_low_pc afterwards. So, we create a
mapping between 'inlined label' and DBG_LABEL MachineInstr in DebugHandlerBase.
The DBG_LABEL in the mapping is used to query the symbol before it.
The AbstractLabels in DwarfCompileUnit is used to process labels in inlined
functions.
We also keep a mapping between scope and labels in DwarfFile to help to
generate correct tree structure of DIEs.
It also generates label debug information under global isel.
Differential Revision: https://reviews.llvm.org/D45556
llvm-svn: 339676
This revision implements support for generating DWARFv5 .debug_addr section.
The implementation is pretty straight-forward: we just check the dwarf version
and emit section header if needed.
Reviewers: aprantl, dblaikie, probinson
Reviewed by: dblaikie
Differential Revision: https://reviews.llvm.org/D50005
llvm-svn: 338487
There are two forms for label debug information in DWARF format.
1. Labels in a non-inlined function:
DW_TAG_label
DW_AT_name
DW_AT_decl_file
DW_AT_decl_line
DW_AT_low_pc
2. Labels in an inlined function:
DW_TAG_label
DW_AT_abstract_origin
DW_AT_low_pc
We will collect label information from DBG_LABEL. Before every DBG_LABEL,
we will generate a temporary symbol to denote the location of the label.
The symbol could be used to get DW_AT_low_pc afterwards. So, we create a
mapping between 'inlined label' and DBG_LABEL MachineInstr in DebugHandlerBase.
The DBG_LABEL in the mapping is used to query the symbol before it.
The AbstractLabels in DwarfCompileUnit is used to process labels in inlined
functions.
We also keep a mapping between scope and labels in DwarfFile to help to
generate correct tree structure of DIEs.
It also generates label debug information under global isel.
Differential Revision: https://reviews.llvm.org/D45556
llvm-svn: 338390
The test failure was caused by the compiler not emitting a __debug_ranges section with DWARF 4 and
earlier when no ranges are needed. The test checks for the existence regardless.
llvm-svn: 338081
There are two forms for label debug information in DWARF format.
1. Labels in a non-inlined function:
DW_TAG_label
DW_AT_name
DW_AT_decl_file
DW_AT_decl_line
DW_AT_low_pc
2. Labels in an inlined function:
DW_TAG_label
DW_AT_abstract_origin
DW_AT_low_pc
We will collect label information from DBG_LABEL. Before every DBG_LABEL,
we will generate a temporary symbol to denote the location of the label.
The symbol could be used to get DW_AT_low_pc afterwards. So, we create a
mapping between 'inlined label' and DBG_LABEL MachineInstr in DebugHandlerBase.
The DBG_LABEL in the mapping is used to query the symbol before it.
The AbstractLabels in DwarfCompileUnit is used to process labels in inlined
functions.
We also keep a mapping between scope and labels in DwarfFile to help to
generate correct tree structure of DIEs.
Differential Revision: https://reviews.llvm.org/D45556
Patch by Hsiangkai Wang.
llvm-svn: 337799
Summary:
Each of the four methods had a dozen lines and was doing almost exactly
the same thing: get the appropriate accelerator table kind and insert an
entry into it. I move this common logic to a helper function and make
these methods delegate to it.
This came up in the context of D49493, where I've needed to make adding
a string to a string pool slightly more complicated, and it seemed to
make sense to do it in one place instead of five.
To make this work I've needed to unify the interface of the AccelTable
data types, as some used to store DIE& and others DIE*. I chose to unify
to a reference as that's what the caller uses.
This technically isn't NFC, because it changes the StringPool used for
apple tables in the DWO case (now it uses the main file like DWARF v5
instead of the DWO file). However, that shouldn't matter, as DWO is not
a thing on apple targets (clang frontend simply ignores -gsplit-dwarf).
Reviewers: JDevlieghere, aprantl, probinson
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D49542
llvm-svn: 337562
Summary:
This patch makes us generate the debug_names section in response to some
user-facing commands (previously it was only generated if explicitly
selected via the -accel-tables option).
My goal was to make this work for DWARF>=5 (as it's an official part of
that standard), and also, as an extension, for DWARF<5 if one is
explicitly tuning for lldb as a debugger (because it brings a large
performance improvement there).
This is slightly complicated by the fact that the debug_names tables are
incompatible with the DWARF v4 type units (they assume that the type
units are in the debug_info section), and unfortunately, right now we
generate DWARF v4-style type units even for -gdwarf-5. For this reason,
I disable all accelerator tables if the user requested type unit
generation. I do this even for apple tables, as they have the same
problem (in fact generating type units for apple targets makes us crash
even before we get around to emitting the accelerator tables).
Reviewers: JDevlieghere, aprantl, dblaikie, echristo, probinson
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D49420
llvm-svn: 337544
and no use of DW_FORM_rnglistx with the DW_AT_ranges attribute.
Reviewer: aprantl
Differential Revision: https://reviews.llvm.org/D49214
llvm-svn: 336927
Summary:
.debug_loc section is not supported for NVPTX target. If there is an
object whose location can change during its lifetime, we do not generate
debug location info for this variable.
Reviewers: echristo
Subscribers: jholewinski, JDevlieghere, llvm-commits
Differential Revision: https://reviews.llvm.org/D48730
llvm-svn: 335976
Summary:
Previously we crashed for the combination of the two features because we
tried to reference the dwo CU from the main object file. The fix
consists of two items:
- reference the skeleton CU from the name index (the consumer is
expected to use the skeleton CU to find the real data).
- use the main object file string pool for the strings in the index
Reviewers: JDevlieghere, aprantl, dblaikie
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D45566
llvm-svn: 330249
Some compilers do not like having an enum type and a variable with the
same name (AccelTableKind). I rename the variable to TheAccelTableKind.
Suggestions for a better name welcome.
llvm-svn: 329202
- MSVC was not OK with a static_assert referencing a non-static member
variable, even though it was just in a sizeof(expression). I move the
assert into the emit function, where it is probably more useful.
- Tests were failing in builds which did not have the X86 target
configured. Since this functionality is not target-specific, I have
removed the target specifiers from the .ll files.
llvm-svn: 329201
Summary:
This patch adds a DwarfAccelTableEmitter class, which generates an
accelerator table, as specified in DWARF v5 standard. At the moment it
only generates a DIE offset column and (if we are indexing more than one
compile unit) a CU column.
Indexing type units is not currently supported, as we don't even have
the ability to generate DWARF v5-compatible compile units.
The implementation is not data-source agnostic like the one generating
apple tables. This was not necessary as we currently only have one user
of this code, and without a second user it was not obvious to me how to
best abstract this. (The difference between these tables and the apple
ones is that they need a lot more metadata about the debug info they are
indexing).
The generation is triggered by the --accel-tables argument, which
supersedes the --dwarf-accel-tables arg -- the latter was a simple
on-off switch, but not we can choose between two kinds of accelerator
tables we can generate.
This is tested by parsing the generated tables with llvm-dwarfdump and
the DWARFVerifier, and I've also checked that GNU readelf is able to
make sense of the tables.
Differential Revision: https://reviews.llvm.org/D43286
llvm-svn: 329179
If a given split type unit does not have source locations, don't have
it refer to the split line table.
If no split type unit refers to the split line table, don't emit the
line table at all.
This will save a little space on rare occasions, but also refactors
things a bit to improve which class is responsible for what.
Responding to review comments on r326395.
Differential Revision: https://reviews.llvm.org/D44220
llvm-svn: 328670
Summary:
Some targets does not support labels inside debug sections, but support
references in form `section+offset`. Patch adds initial support
for this.
Reviewers: echristo, probinson, jlebar
Subscribers: llvm-commits, JDevlieghere
Differential Revision: https://reviews.llvm.org/D43943
llvm-svn: 328314
Summary:
Added a flag -no-dwarf-pub-sections, which allows to disable
emission of DWARF public sections.
Reviewers: probinson, echristo
Subscribers: aprantl, JDevlieghere, llvm-commits
Differential Revision: https://reviews.llvm.org/D44385
llvm-svn: 327994
Summary:
Some targets does not support labels inside debug sections, but support
references in form `section +|- offset`. Patch adds initial support
for this. Also, this patch disables emission of all additional debug
sections that may have labels inside of it (like pub sections and
string tables).
Reviewers: probinson, echristo
Subscribers: JDevlieghere, llvm-commits
Differential Revision: https://reviews.llvm.org/D43627
llvm-svn: 326328
Summary:
This commit separates the abstract accelerator table data structure
from the code for writing out an on-disk representation of a specific
accelerator table format. The idea is that former (now called
AccelTable<T>) can be reused for the DWARF v5 accelerator tables
as-is, without any further customizations.
Some bits of the emission code (now living in the EmissionContext class)
can be reused for DWARF v5 as well, but the subtle differences in the
layout of various subtables mean the sharing is not always possible.
(Also, the individual emit*** functions are fairly simple so there's a
tradeoff between making a bigger general-purpose function, and two
smaller targeted functions.)
Another advantage of this setup is that more of the serialization logic
can be hidden in the .cpp file -- I have moved declarations of the
header and all the emission functions there.
Reviewers: JDevlieghere, aprantl, probinson, dblaikie
Subscribers: echristo, clayborg, vleschuk, llvm-commits
Differential Revision: https://reviews.llvm.org/D43285
llvm-svn: 325516
This patch renames DwarfAccelTable.{h,cpp} to AccelTable.{h,cpp} and
moves the header to the include dir so it is accessible by the
dsymutil implementation.
Differential revision: https://reviews.llvm.org/D42529
llvm-svn: 323654
This patch refactors the way data is stored in the accelerator table and
makes them truly generic. There have been several attempts to do this in
the past:
- D8215 & D8216: Using a union and partial hardcoding.
- D11805: Using inheritance.
- D42246: Using a callback.
In the end I didn't like either of them, because for some reason or
another parts of it felt hacky or decreased runtime performance. I
didn't want to completely rewrite them as I was hoping that we could
reuse parts for the successor in the DWARF standard. However, it seems
less and less likely that there will be a lot of opportunities for
sharing code and/or an interface.
Originally I choose to template the whole class, because it introduces
no performance overhead compared to the original implementation.
We ended up settling on a hybrid between a templated method and a
virtual call to emit the data. The motivation is that we don't want to
increase code size for a feature that should soon be superseded by the
DWARFv5 accelerator tables. While the code will continue to be used for
compatibility, it won't be on the hot path. Furthermore this does not
regress performance compared to Apple's internal implementation that
already uses virtual calls for this.
A quick summary for why these changes are necessary: dsymutil likes to
reuse the current implementation of the Apple accelerator tables.
However, LLDB expects a slightly different interface than what is
currently emitted. Additionally, in dsymutil we only have offsets and no
actual DIEs.
Although the patch suggests a lot of code has changed, this change is
pretty straightforward:
- We created an abstract class `AppleAccelTableData` to serve as an
interface for the different data classes.
- We created two implementations of this class, one for type tables and
one for everything else. There will be a third one for dsymutil that
takes just the offset.
- We use the supplied class to deduct the atoms for the header which
makes the structure of the table fully self contained, although not
enforced by the interface as was the case for the fully templated
approach.
- We renamed the prefix from DWARF- to Apple- to make space for the
future implementation of .debug_names.
This change is NFC and relies on the existing tests.
Differential revision: https://reviews.llvm.org/D42334
llvm-svn: 323653
Markus Lavin