glibc and linux kernel use size_t for some field lengths while POSIX and
musl use int. This bug would have caused breakage the first time someone
tried to call sendmsg on a 64-bit big endian system when linking musl
libc.
my opinion:
* msghdr.iovlen: kernel and glibc have it right. This field should
definitely be size_t. With int, the padding bytes are wasted for no
reason.
* msghdr.controllen: POSIX and musl have it right. 4 bytes is plenty for
the length, and it saves 4 bytes next to flags.
* cmsghdr.len: POSIX and musl have it right. 4 bytes is plenty for the
length, and it saves 4 bytes since the other fields are also 32-bits
each.
The one about INT_MAX is self-evident from the type system.
The one about kernel having bad types doesn't seem accurate as I checked
the source code and it uses size_t for all the appropriate types,
matching the libc struct definition for msghdr and msghdr_const.
MIPS I has load hazards so we need to insert nops in a few places. This is not a
problem for MIPS II and later.
While doing this, I also touched up all the inline asm to use ABI register
aliases and a consistent formatting convention. Also fixed a few places that
didn't properly check if the syscall return value should be negated.
The compile-time check against the minimum version here wasn't appropriate, since it still makes sense to try using FILE_RENAME_INFORMATION_EX even if the minimum version is something like `xp`, since that doesn't rule out the possibility of the compiled code running on Windows 10/11. This compile-time check was doubly bad since the default minimum windows version (`.win10`) was below the `.win10_rs5` that was checked for, so when providing a target like `x86_64-windows-gnu` it'd always rule out using this syscall.
After this commit, we always try using FILE_RENAME_INFORMATION_EX and then let the operating system tell us when some aspect of it is not supported. This allows us to get the benefits of these new syscalls/flags whenever it's actually possible.
The possible error returns were validated experimentally:
- INVALID_PARAMETER is returned when the underlying filesystem is FAT32
- INVALID_INFO_CLASS is returned on Windows 7 when trying to use FileRenameInformationEx/FileDispositionInformationEx
- NOT_SUPPORTED is returned on Windows 10 >= .win10_rs5 when setting a bogus flag value (I used `0x1000`)
This is very likely full of wrong stuff. It's effectively just a copy of the
x86_64 file - needed because the former stopped using usize/isize. To be clear,
this is no more broken than the old situation was; this just makes the
brokenness explicit.
This is very likely full of wrong stuff. It's effectively just a copy of the
mips64 file - needed because the former stopped using usize/isize. To be clear,
this is no more broken than the old situation was; this just makes the
brokenness explicit.
This type is useful for two things:
* Doing non-local control flow with ucontext.h functions.
* Inspecting machine state in a signal handler.
The first use case is not one we support; we no longer expose bindings to those
functions in the standard library. They're also deprecated in POSIX and, as a
result, not available in musl.
The second use case is valid, but is very poorly served by the standard library.
As evidenced by my changes to std.debug.cpu_context.signal_context_t, users will
be better served rolling their own ucontext_t and especially mcontext_t types
which fit their specific situation. Further, these types tend to evolve
frequently as architectures evolve, and the standard library has not done a good
job keeping up, or even providing them for all supported targets.
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: #23801Resolves: #23802
It was possible for `arg6` to be passed as an operand relative to esp.
In that case, the `push` at the top clobbered esp and hence made the
reference to arg6 invalid. This was manifesting in this branch as broken
stack traces on x86-linux due to an `mmap2` syscall accidentally passing
the page offset as non-zero!
This commit fixes a bug introduced in cb0e6d8aa.
