The kernel does define the struct, it just doesn't use it. Yet both glibc and
musl expose it directly as their public stat struct, and std.c takes it from
std.os.linux. So just define it after all.
The compiler actually doesn't need any functional changes for this: Sema
does reification based on the tag indices of `std.builtin.Type` already!
So, no zig1.wasm update is necessary.
This change is necessary to disallow name clashes between fields and
decls on a type, which is a prerequisite of #9938.
The kernel sets r7 to 0 (success) or -1 (error), and stores the result in r2.
When r7 is -1 and the result is positive, it needs to be negated to get the
errno value that higher-level code, such as errnoFromSyscall(), expects to see.
The old code was missing the check that r2 is positive, but was also doing the
r7 check incorrectly; since it can only be set to 0 or -1, the blez instruction
would always branch.
In practice, this fix is necessary for e.g. the ENOSYS error to be interpreted
correctly. This manifested as hitting an unreachable branch when calling
process_vm_readv() in std.debug.MemoryAccessor.
What is `sparcel`, you might ask? Good question!
If you take a peek in the SPARC v8 manual, §2.2, it is quite explicit that SPARC
v8 is a big-endian architecture. No little-endian or mixed-endian support to be
found here.
On the other hand, the SPARC v9 manual, in §3.2.1.2, states that it has support
for mixed-endian operation, with big-endian mode being the default.
Ok, so `sparcel` must just be referring to SPARC v9 running in little-endian
mode, surely?
Nope:
* 40b4fd7a3e/llvm/lib/Target/Sparc/SparcTargetMachine.cpp (L226)
* 40b4fd7a3e/llvm/lib/Target/Sparc/SparcTargetMachine.cpp (L104)
So, `sparcel` in LLVM is referring to some sort of fantastical little-endian
SPARC v8 architecture. I've scoured the internet and I can find absolutely no
evidence that such a thing exists or has ever existed. In fact, I can find no
evidence that a little-endian implementation of SPARC v9 ever existed, either.
Or any SPARC version, actually!
The support was added here: https://reviews.llvm.org/D8741
Notably, there is no mention whatsoever of what CPU this might be referring to,
and no justification given for the "but some are little" comment added in the
patch.
My best guess is that this might have been some private exercise in creating a
little-endian version of SPARC that never saw the light of day. Given that SPARC
v8 explicitly doesn't support little-endian operation (let alone little-endian
instruction encoding!), and no CPU is known to be implemented as such, I think
it's very reasonable for us to just remove this support.
* Elaborate on the sub-variants of Variant I.
* Clarify the use of the TCB term.
* Rename a bunch of stuff to be more accurate/descriptive.
* Follow Zig's style around namespacing more.
* Use a structure for the ABI TCB.
No functional change intended.
The code would cause LLVM to emit a jump table for the switch in the loop over
the dynamic tags. That jump table was far enough away that the compiler decided
to go through the GOT, which would of course break at this early stage as we
haven't applied MIPS's local GOT relocations yet, nor can we until we've walked
through the _DYNAMIC array.
The first attempt at rewriting this used code like this:
var sorted_dynv = [_]elf.Addr{0} ** elf.DT_NUM;
But this is also problematic as it results in a memcpy() call. Instead, we
explicitly initialize it to undefined and use a loop of volatile stores to
clear it.
