openkal-musl 0.3.0

musl 1.2.5 redirected onto openkal, running
on Linux, macOS and Windows.

The package was openkal-libc up to 0.2.0 — a probe of 243 lines exporting 14
names, which was not a C library. The version line continues rather than
restarting: a tag is the one thing in the release chain that cannot be given a
second meaning.

The shape of the port

musl reaches its environment through one seam: seven inline functions in
arch/<arch>/syscall_arch.h, plus __get_tp in pthread_arch.h. Replacing that
one header is the whole of the redirection, and 1345 sources are compiled
unmodified.

musl/PATCHES.md lists the whole of what is not unmodified: four patched
lines and nine replaced sources, each with its reason.

	lines
the system-call correspondence	923
descriptors and name resolution	434
startup and the thread pointer	241
setjmp and its relatives	223
execution contexts and the suspension primitive	202
starting another program	163
where per-context state is kept	128
what two object formats do not provide	105
how a second name is made	133
the rest	241
total	2793

Against 1345 musl sources compiled unmodified. Between the first system and the
third the port grew by 800 lines, and every one of those is about an object
format or a naming convention rather than about a kernel.

Three object formats

ELF	the reference case
PE	measured, with both toolchains: a weak symbol is not a definition there. The 289 aliases are made strongly, and the 46 names musl provides as placeholders are not made at all — decided by the name of the placeholder's target, so no site of musl's is edited
Mach-O	the compiler refuses the construct: aliases are not supported on darwin. The assembler's directive makes the name instead, and the same placeholder list applies

Four findings that only running produced

A C library cannot keep its per-context state in a thread_local variable. On
one toolchain such a variable is reached through a helper that allocates, and the
allocator is what the C library provides.

long double is not a property of the architecture alone. On Apple arm64 it
is 53 bits where musl's arch/aarch64/bits/float.h says 113 — measured on all
four combinations. printf("%.3f", 1.5) stopped in frexpl with the value read
as infinity. port/src/okm_float_assert.c now asserts the agreement.

A program above this library must not have a C++ runtime embedded into it. On
one system the build tool embeds one and runs its initialiser before the entry
point, when the C library has not started.

An object format's linker divides a section into atoms, and a section with no
content has no atom — the four names musl walks between went missing with it.

What runs above it

examples/posix	32 observations, on all three systems
examples/wordcount	the same counts as the system's own wc
mcpplibs/sbase	all 97 suckless base utilities, sources unmodified, 50 comparisons

Continuous integration: Linux (gcc, llvm), macOS (llvm), Windows (gcc, PE).