[LLVM] Use {} instead of std::nullopt to initialize empty ArrayRef (#109133)

It is almost always simpler to use {} instead of std::nullopt to
initialize an empty ArrayRef. This patch changes all oc

[LLVM] Use {} instead of std::nullopt to initialize empty ArrayRef (#109133)

It is almost always simpler to use {} instead of std::nullopt to
initialize an empty ArrayRef. This patch changes all occurrences I could
find in LLVM itself. In future the ArrayRef(std::nullopt_t) constructor
could be deprecated or removed.

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[llvm] Construct SmallVector with ArrayRef (NFC) (#101872)

[Object] Fix handling of Elf_Nhdr with sh_addralign=8

The generic ABI says:

> Padding is present, if necessary, to ensure 8 or 4-byte alignment for the next note entry (depending on whether the fil

[Object] Fix handling of Elf_Nhdr with sh_addralign=8

The generic ABI says:

> Padding is present, if necessary, to ensure 8 or 4-byte alignment for the next note entry (depending on whether the file is a 64-bit or 32-bit object). Such padding is not included in descsz.

Our parsing code currently aligns n_namesz. Fix the bug by aligning the start
offset of the descriptor instead. This issue has been benign because the primary
uses of sh_addralign=8 notes are `.note.gnu.property`, where
`sizeof(Elf_Nhdr) + sizeof("GNU") = 16` (already aligned by 8).

In practice, many 64-bit systems incorrectly use sh_addralign=4 notes.
We can use sh_addralign (= p_align) to decide the descriptor padding.
Treat an alignment of 0 and 1 as 4. This approach matches modern GNU readelf
(since 2018).

We have a few tests incorrectly using sh_addralign=0. We may make our behavior
stricter after fixing these tests.

Linux kernel dumped core files use `p_align=0` notes, so we need to support the
case for compatibility.

Reviewed By: jhenderson

Differential Revision: https://reviews.llvm.org/D150022

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[Object] Refactor build ID parsing into Object lib.

This makes parsing for build IDs in the markup filter slightly more
permissive, in line with fromHex.

It also removes the distinction between mis

[Object] Refactor build ID parsing into Object lib.

This makes parsing for build IDs in the markup filter slightly more
permissive, in line with fromHex.

It also removes the distinction between missing build ID and empty build
ID; empty build IDs aren't a useful concept, since their purpose is to
uniquely identify a binary. This removes a layer of indirection wherever
build IDs are obtained.

Reviewed By: jhenderson

Differential Revision: https://reviews.llvm.org/D147485

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[Object] llvm::Optional => std::optional

[llvm] Use std::nullopt instead of None (NFC)

This patch mechanically replaces None with std::nullopt where the
compiler would warn if None were deprecated. The intent is to reduce
the amount of ma

[llvm] Use std::nullopt instead of None (NFC)

This patch mechanically replaces None with std::nullopt where the
compiler would warn if None were deprecated. The intent is to reduce
the amount of manual work required in migrating from Optional to
std::optional.

This is part of an effort to migrate from llvm::Optional to
std::optional:

https://discourse.llvm.org/t/deprecating-llvm-optional-x-hasvalue-getvalue-getvalueor/63716

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[NFC] [Object] Create library to fetch debug info by build ID.

This creates a library for fetching debug info by build ID, whether
locally or remotely via debuginfod. The functionality was refactore

[NFC] [Object] Create library to fetch debug info by build ID.

This creates a library for fetching debug info by build ID, whether
locally or remotely via debuginfod. The functionality was refactored
out of existing code in the Symboliize library. Existing utilities
were refactored to use this library.

Reviewed By: phosek

Differential Revision: https://reviews.llvm.org/D132504

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