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[Backtracing][Linux] Add Linux support to swift-backtrace. #66410

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merged 17 commits into from Jun 7, 2023

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@al45tair al45tair commented Jun 7, 2023

We need a Linux specific Target implementation, and a couple of minor tweaks to make things build everywhere.

rdar://110262673

This also adds a function to demangle a symbol, and a way for the
backtracing code to report warning messages to the same place as
the main runtime.

I'd like to rename the _swift_isThunkFunction() SPI also, but we
can't do that until we've made the changes to the _Backtracing
library, so we'll do that there instead.

rdar://110261430
This was added to a later PR, but not to this one, though we need
it here.

rdar://110261430
This should have been disabled until apple#66338.

rdar://110261430
Mike and Max made various helpful suggestions, so I've added and updated
various comments and amended the code to cope with partial reads and
writes.

rdar://110261430
Moved the comment for `_swift_backtrace_demangle` into the header file
instead of it being in the implementation.

rdar://110261430
The Swift backtracer's frame pointer unwinder cannot work on Linux
without this change, because the compiler omits the frame pointer from
the function in libSwift_Backtracing that actually captures the stack.

rdar://110260855
Using `SwiftShims` is undesirable - it creates all kinds of build issues,
and means shipping the `_SwiftBacktracing.h` header in the SDK, which is
not necessary.

While we're doing this, add the necessary definitions for reading ELF
and DWARF information.

rdar://110261712
Use the new module structure rather the old SwiftShims header.  This
is much cleaner and lets us include operating system headers to get
the relevant definitions where possible.

Add code to support ELF and DWARF, including decompression using
zlib, zstd and liblzma if those turn out to be required and available.

rdar://110261712
This is for compatibility, so that I can split up the PRs.
We'll remove it in the next PR.

rdar://110261712
There's a chance that pipes might perform a partial read; we should
handle that case.

rdar://110261712
The `status` argument to the `_swift_backtrace_demangle()` function
isn't especially useful, won't match behaviour on Windows, and we
actually don't use it in the Swift code that calls this SPI.

Remove it.

rdar://110261712
`__cxa_demangle()` is a rather unusual API; one of its "features" is that
the pointer you pass in must either be `nullptr`, in which case it
will call `malloc()` itself, _or_ it has to be a pointer to a block
of memory allocated with `malloc()`, because `__cxa_demangle()` may
`realloc()` it for you.

This seems to me to be something of a non-obvious footgun, so we never
pass the caller's pointer through to `__cxa_demangle()`, which lets them
decide how they want to allocate space.

rdar://110261712
…ule.

There's a separate declaration here because we can't include the `Backtrace.h`
header from inside `modules/Runtime/Runtime.h`.

rdar://110261712
The `_Backtracing` module has a number of private implementation only
imports that aren't used outside of the module and that don't require
any additional libraries (hence they aren't relevant to the outside
world).  `verify_all_overlays.py` needs to know about these when it
does its test, because it loadas the module as the main module, which
results in implementation only imports being required instead of
ignored.

rdar://110261712
We need a Linux specific `Target` implementation, and a couple of minor
tweaks to make things build everywhere.

rdar://110262673
We don't need these here.  They were a leftover from previous code.

rdar://110262673
@al45tair al45tair added 🍒 release cherry pick Flag: Release branch cherry picks swift 5.9 labels Jun 7, 2023
@al45tair al45tair requested a review from a team as a code owner June 7, 2023 12:34
@al45tair
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al45tair commented Jun 7, 2023

This is built on #66408 and includes all of its commits. The first commit that actually forms part of this PR is 7cc2446.

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al45tair commented Jun 7, 2023

Explanation: Adds the necessary code to the swift-backtrace executable to support Linux.
Risk: Low. Only affects Linux, and this code is disabled until the later enabling PR.
Original PR: #66337
Reviewed by: @MaxDesiatov
Resolves: rdar://110262673
Tests: The Linux backtracing tests exercise this code (but those are in the enabling PR as they won't work until this is enabled).

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al45tair commented Jun 7, 2023

@swift-ci Please test

@al45tair al45tair merged commit 45339b6 into apple:release/5.9 Jun 7, 2023
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