[BPF][DebugInfo] Use .BPF.ext for line info when DWARF is not available

"BTF" is a debug information format used by LLVM's BPF backend.
The format is much smaller in scope than DWARF, the following

[BPF][DebugInfo] Use .BPF.ext for line info when DWARF is not available

"BTF" is a debug information format used by LLVM's BPF backend.
The format is much smaller in scope than DWARF, the following info is
available:
- full set of C types used in the binary file;
- types for global values;
- line number / line source code information .

BTF information is embedded in ELF as .BTF and .BTF.ext sections.
Detailed format description could be found as a part of Linux Source
tree, e.g. here: [1].

This commit modifies `llvm-objdump` utility to use line number
information provided by BTF if DWARF information is not available.
E.g., the goal is to make the following to print source code lines,
interleaved with disassembly:

$ clang --target=bpf -g test.c -o test.o
$ llvm-strip --strip-debug test.o
$ llvm-objdump -Sd test.o

test.o: file format elf64-bpf

Disassembly of section .text:

<foo>:
; void foo(void) {
r1 = 0x1
; consume(1);
call -0x1
r1 = 0x2
; consume(2);
call -0x1
; }
exit

A common production use case for BPF programs is to:
- compile separate object files using clang with `-g -c` flags;
- link these files as a final "static" binary using bpftool linker ([2]).
The bpftool linker discards most of the DWARF sections
(line information sections as well) but merges .BTF and .BTF.ext sections.
Hence, having `llvm-objdump` capable to print source code using .BTF.ext
is valuable.

The commit consists of the following modifications:

- llvm/lib/DebugInfo/BTF aka `DebugInfoBTF` component is added to host
the code needed to process BTF (with assumption that BTF support
would be added to some other tools as well, e.g. `llvm-readelf`):
- `DebugInfoBTF` provides `llvm::BTFParser` class, that loads information
from `.BTF` and `.BTF.ext` sections of a given `object::ObjectFile`
instance and allows to query this information.
Currently only line number information is loaded.

- `DebugInfoBTF` also provides `llvm::BTFContext` class, which is an
implementation of `DIContext` interface, used by `llvm-objdump` to
query information about line numbers corresponding to specific
instructions.

- Structure `DILineInfo` is modified with field `LineSource`.

`DIContext` interface uses `DILineInfo` structure to communicate
line number and source code information.
Specifically, `DILineInfo::Source` field encodes full file source code,
if available. BTF only stores source code for selected lines of the
file, not a complete source file. Moreover, stored lines are not
guaranteed to be sorted in a specific order.

To avoid reconstruction of a file source code from a set of
available lines, this commit adds `LineSource` field instead.

- `Symbolize` class is modified to use `BTFContext` instead of
`DWARFContext` when DWARF sections are not available but BTF
sections are present in the object file.
(`Symbolize` is instantiated by `llvm-objdump`).

- Integration and unit tests.

Note, that DWARF has a notion of "instruction sequence".
DWARF implementation of `DIContext::getLineInfoForAddress()` provides
inexact responses if exact address information is not available but
address falls within "instruction sequence" with some known line
information (see `DWARFDebugLine::LineTable::findRowInSeq()`).

BTF does not provide instruction sequence groupings, thus
`getLineInfoForAddress()` queries only return exact matches.
This does not seem to be a big issue in practice, but output
of the `llvm-objdump -Sd` might differ slightly when BTF
is used instead of DWARF.

[1] https://www.kernel.org/doc/html/latest/bpf/btf.html
[2] https://github.com/libbpf/bpftool

Depends on https://reviews.llvm.org/D149501

Reviewed By: MaskRay, yonghong-song, nickdesaulniers, #debug-info

Differential Revision: https://reviews.llvm.org/D149058

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Remove the dependency between lib/DebugInfoDWARF and MC.

Differential Revision: https://reviews.llvm.org/D134817

Revert "Remove the dependency between lib/DebugInfoDWARF and MC."

This reverts commit 7dde94251e1c9e4634f5d51d41f2d4a191258fb3.

Because of test failures:

lldb-shell :: SymbolFile/DWARF/x86/DW_AT

Revert "Remove the dependency between lib/DebugInfoDWARF and MC."

This reverts commit 7dde94251e1c9e4634f5d51d41f2d4a191258fb3.

Because of test failures:

lldb-shell :: SymbolFile/DWARF/x86/DW_AT_loclists_base.s
lldb-shell :: SymbolFile/DWARF/x86/debug_loc.s
lldb-shell :: SymbolFile/DWARF/x86/debug_loc_and_loclists.s
lldb-shell :: SymbolFile/DWARF/x86/debug_loclists-dwo.s
lldb-shell :: SymbolFile/DWARF/x86/debug_loclists-dwp.s
lldb-shell :: SymbolFile/DWARF/x86/dwp.s
lldb-shell :: SymbolFile/DWARF/x86/unused-inlined-params.test
lldb-shell :: SymbolFile/NativePDB/inline_sites.test
lldb-shell :: SymbolFile/NativePDB/local-variables-registers.s
lldb-shell :: SymbolFile/NativePDB/nested-blocks-same-address.s

show more ...

Remove the dependency between lib/DebugInfoDWARF and MC.

Differential Revision: https://reviews.llvm.org/D134817

Revert "Remove the dependency between lib/DebugInfoDWARF and MC."

This reverts commit d96ade00c3c96bd451c60e34a17e613cdd5fdc38.

Remove the dependency between lib/DebugInfoDWARF and MC.

This patch had to be reverted because on gcc 7.5.0 we see an error converting from std::unique_ptr<MCRegisterInfo> to Expected<std::unique_pt

Remove the dependency between lib/DebugInfoDWARF and MC.

This patch had to be reverted because on gcc 7.5.0 we see an error converting from std::unique_ptr<MCRegisterInfo> to Expected<std::unique_ptr<MCRegisterInfo>> as the return type for the function createRegInfo. This has now been fixed.

show more ...

Revert "Remove the dependency between lib/DebugInfoDWARF and MC."

This reverts commit 0008990479a2daf587c2a4f274384b2fb87247fb.

Remove the dependency between lib/DebugInfoDWARF and MC.

Differential Revision: https://reviews.llvm.org/D134817

Cleanup LLVMObject headers

Most notably,

llvm/Object/Binary.h no longer includes llvm/Support/MemoryBuffer.h
llvm/Object/MachOUniversal*.h no longer include llvm/Object/Archive.h
llvm/Object/TapiUn

Cleanup LLVMObject headers

Most notably,

llvm/Object/Binary.h no longer includes llvm/Support/MemoryBuffer.h
llvm/Object/MachOUniversal*.h no longer include llvm/Object/Archive.h
llvm/Object/TapiUniversal.h no longer includes llvm/Object/TapiFile.h

llvm-project preprocessed size:
before: 1068185081
after: 1068324320

Discourse thread: https://discourse.llvm.org/t/include-what-you-use-include-cleanup
Differential Revision: https://reviews.llvm.org/D119457

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[llvm] Remove redundant member initialization (NFC)

Identified with readability-redundant-member-init.

Revert "[llvm] Remove redundant member initialization (NFC)"

This reverts commit fd4808887ee47f3ec8a030e9211169ef4fb094c3.

This patch causes gcc to issue a lot of warnings like:

warning: base cl

Revert "[llvm] Remove redundant member initialization (NFC)"

This reverts commit fd4808887ee47f3ec8a030e9211169ef4fb094c3.

This patch causes gcc to issue a lot of warnings like:

warning: base class ‘class llvm::MCParsedAsmOperand’ should be
explicitly initialized in the copy constructor [-Wextra]

show more ...

[llvm] Remove redundant member initialization (NFC)

Identified with readability-redundant-member-init.

llvm-objdump: refactor SourcePrinter into separate file. NFC.

Preparatory patch for MachO feature.