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Oleksandr ShyshatskyiandClaude Opus 5
99706bb5f7
The Bootlin swap two commits ago (musl.cc -> mips32el) fixed a
reachability problem and kept a correctness one: mips32el is plain
mips32r1, whose musl crt/libc is legacy-NaN by construction and cannot
be made to emit nan2008 output at all -- forcing -mnan=2008 on it fails
to LINK ("mixing -mnan=2008 module with previous -mnan=legacy modules").
So every s6 binary this repo has shipped read e_flags=0x1007, defended
in five separate places as correct on the theory that a supervisor
doing no floating point cannot care about NaN encoding.
True of the arithmetic. False of exec(): docs/how-it-works.md already
documented, for a different binary, that "the Ingenic X2000 kernel
returns ENOEXEC for legacy-NaN MIPS" -- the ABI check happens before a
single instruction of the program's own runs, which means it was never
about what s6 computes. None of the replica gates that "measured s6
working on the printer" ever caught this, because none of them ran on
the printer: qemu-mipsel-static's user-mode emulation does not enforce
the same ABI check a real kernel's binfmt loader does. A build that
passed case-supervisor.sh, case-services.sh, case-moonraker313-s6.sh and
a full release run was still shipping a supervisor that a real X2000
kernel may refuse to start at all.
THE FIX. Bootlin also publishes mips32r5el: MIPS Release 5 has no
legacy-NaN silicon to be compatible with, so its musl crt/libc is
nan2008 by construction, and its default codegen already targets
mips32r2. Verified outside the repo before touching anything: fetched
the tarball, cross-compiled skalibs+s6 with it, every binary read
nan2008/o32/mips32r2, and s6-svscan ran and supervised under
qemu-mipsel-static. Section 5b now applies the same gcc-wrapper
discipline 5c already uses for the Ingenic toolchain -- -EL -mnan=2008
-march=mips32r2 baked into the driver, not left to CFLAGS, with a probe
gate before building anything on top -- because "the toolchain's default
happens to be right" is exactly the kind of assumption this bug was.
mips_abi_gate moved earlier in the file so 5b can use it, and s6 is IN
that gate now rather than exempt from it -- exempt is how this shipped
wrong for as long as it did. The gate itself grew a real relaxation
alongside the real tightening: a static EXEC from this musl toolchain
legitimately carries EF_MIPS_PIC (musl's crt is unconditionally -fPIC;
no combination of -static/-no-pie/-fno-PIC removes it, measured) and so
reads the DYN flag value anyway, which is a property of the toolchain
and not a sign of anything wrong -- so the gate now accepts either
0x70001405 or 0x70001407 for any object, rather than picking one from
the ELF Type.
Also bumped S6_STAMP to include MUSL_TOOLCHAIN_FILE: without that, a
checkout with an already-built work/.s6 from before this commit would
read its own stale legacy-NaN tree as current and never rebuild it.
Full real build: "s6: 14 ELF objects are nan2008/o32/mips32r2 -- good".
case-supervisor.sh green on the replica with the new binaries.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>