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Our usage of `ucontext_t` in the standard library was kind of
problematic. We unnecessarily mimiced libc-specific structures, and our
`getcontext` implementation was overkill for our use case of stack
tracing.
This commit introduces a new namespace, `std.debug.cpu_context`, which
contains "context" types for various architectures (currently x86,
x86_64, ARM, and AARCH64) containing the general-purpose CPU registers;
the ones needed in practice for stack unwinding. Each implementation has
a function `current` which populates the structure using inline
assembly. The structure is user-overrideable, though that should only be
necessary if the standard library does not have an implementation for
the *architecture*: that is to say, none of this is OS-dependent.
Of course, in POSIX signal handlers, we get a `ucontext_t` from the
kernel. The function `std.debug.cpu_context.fromPosixSignalContext`
converts this to a `std.debug.cpu_context.Native` with a big ol' target
switch.
This functionality is not exposed from `std.c` or `std.posix`, and
neither are `ucontext_t`, `mcontext_t`, or `getcontext`. The rationale
is that these types and functions do not conform to a specific ABI, and
in fact tend to get updated over time based on CPU features and
extensions; in addition, different libcs use different structures which
are "partially compatible" with the kernel structure. Overall, it's a
mess, but all we need is the kernel context, so we can just define a
kernel-compatible structure as long as we don't claim C compatibility by
putting it in `std.c` or `std.posix`.
This change resulted in a few nice `std.debug` simplifications, but
nothing too noteworthy. However, the main benefit of this change is that
DWARF unwinding---sometimes necessary for collecting stack traces
reliably---now requires far less target-specific integration.
Also fix a bug I noticed in `PageAllocator` (I found this due to a bug
in my distro's QEMU distribution; thanks, broken QEMU patch!) and I
think a couple of minor bugs in `std.debug`.
Resolves: #23801
Resolves: #23802
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It's now user-overrideable, and uses `noreturn` types to neatly stop
analysis.
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The big endian RISC-V effort is mostly driven by MIPS (the company) which is
pivoting to RISC-V, and presumably needs a big endian variant to fill the niche
that big endian MIPS (the ISA) did.
GCC already supports these targets, but LLVM support will only appear in 22;
this commit just adds the necessary target knowledge and checks on our end.
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This struct is larger than 256 bytes and code that copies it
consistently shows up in profiles of the compiler.
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This was for a hobby project that appears to be dormant for now. This can be
added back if the project is resumed in the future.
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Needed for creating libraries that run both on
physical Apple Watches and the watchOS simulator.
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There are two concepts here: one for whether dwarf supports unwinding on
that target, and another for whether the Zig standard library
implements it yet.
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...which have a ucontext_t but not a PC register. The current stack
unwinding implementation does not yet support this architecture.
Also fix name of `std.debug.SelfInfo.openSelf` to remove redundancy.
Also removed this hook into root providing an "openSelfDebugInfo"
function. Sorry, this debugging code is not of sufficient quality to
offer a plugin API right now.
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After this commit:
`std.debug.SelfInfo` is a cross-platform abstraction for the current
executable's own debug information, with a goal of minimal code bloat
and compilation speed penalty.
`std.debug.Dwarf` does not assume the current executable is itself the
thing being debugged, however, it does assume the debug info has the
same CPU architecture and OS as the current executable. It is planned to
remove this limitation.
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std.debug.Dwarf is the parsing/decoding logic. std.dwarf remains the
unopinionated types and bits alone.
If you look at this diff you can see a lot less redundancy in
namespaces.
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