89de963b

fix: the spawn is an exec, not a fork — four comments still said fork

a73x 2026-08-29 02:18

Commit message

fix: the spawn is an exec, not a fork — four comments still said fork

fork-into-run was tried and crashed (a forked child's first
DebugAllocator trace panics in MemoryAccessor), so the child execs this
same image with argv `mux d run …`. Four comments outlived that: the
daemon main's doc, the build's one-binary note, the e2e PATH note and
coverage.sh's tracing note. coverage.sh's conclusion still holds —
ptrace follows an exec — but for a reason it did not state.

`mux d`'s main takes argv because the dispatcher has eaten the mode
word, which is the reason that survives.

build.zig

Old		New
@@ -924,9 +924,10 @@ pub fn build(b: *std.Build) void {
924		924
925	// ONE product binary. The four mains are modules under it, reached by	925	// ONE product binary. The four mains are modules under it, reached by
926	// the mode word rather than by four names on PATH — which is also what	926	// the mode word rather than by four names on PATH — which is also what
927	// lets the client's auto-start fork into the daemon instead of hunting	927	// lets the client's auto-start exec this same image with argv
928	// for a sibling. The fixtures below stay separate: they stand in for	928	// `mux d run …` (spawn.zig) instead of hunting PATH for a sibling. The
929	// users, not for the product.	929	// fixtures below stay separate: they stand in for users, not for the
		930	// product.
930	const mux_exe = b.addExecutable(.{ .name = "mux", .root_module = mux_mod });	931	const mux_exe = b.addExecutable(.{ .name = "mux", .root_module = mux_mod });
931	// Zig 0.15's self-hosted x86_64 linker can't handle the .sframe	932	// Zig 0.15's self-hosted x86_64 linker can't handle the .sframe
932	// sections emitted by gcc >= 16 crt1.o on this system; LLD can.	933	// sections emitted by gcc >= 16 crt1.o on this system; LLD can.

src/cli/main.zig

Old		New
@@ -282,9 +282,9 @@ fn parseBindAddr(s: []const u8) !std.net.Address {
282	return std.net.Address.parseIp(hp.host, hp.port);	282	return std.net.Address.parseIp(hp.host, hp.port);
283	}	283	}
284		284
285	/// `mux d`. argv arrives from the dispatcher rather than from	285	/// `mux d`. argv arrives from the dispatcher, which has already eaten the
286	/// `argsAlloc`, because the local auto-start reaches this entry by fork	286	/// mode word, rather than from `argsAlloc`: one binary, four mains, and
287	/// instead of exec (spawn.zig) and a forked child has no argv of its own.	287	/// only the dispatcher knows where each mode's arguments start.
288	pub fn main(args: []const [:0]const u8) !u8 {	288	pub fn main(args: []const [:0]const u8) !u8 {
289	var gpa: std.heap.DebugAllocator(.{}) = .init;	289	var gpa: std.heap.DebugAllocator(.{}) = .init;
290	defer if (gpa.deinit() == .leak)	290	defer if (gpa.deinit() == .leak)

test/coverage.sh

Old		New
@@ -75,7 +75,8 @@ mkdir -p "$SHIM" "$RAW"
75	# would otherwise run its client traced in silence. The client mode is NOT	75	# would otherwise run its client traced in silence. The client mode is NOT
76	# in the default set, and that is a limitation rather than a preference: a	76	# in the default set, and that is a limitation rather than a preference: a
77	# traced client that auto-starts a daemon can never exit. The daemon is now	77	# traced client that auto-starts a daemon can never exit. The daemon is now
78	# a FORK of the client (spawn.zig) rather than an exec of a sibling, so it	78	# an exec of THIS image from a fork of the client (spawn.zig) rather than of
		79	# a sibling on PATH, and ptrace follows an exec, so it
79	# is traced whenever the client is, stays traced after it reparents to	80	# is traced whenever the client is, stays traced after it reparents to
80	# init, and kcov waits for its last traced descendant — a process designed	81	# init, and kcov waits for its last traced descendant — a process designed
81	# never to end. The auto-start and `--via` legs wedge on this, and a	82	# never to end. The auto-start and `--via` legs wedge on this, and a

test/e2e.sh

Old		New
@@ -23,9 +23,9 @@ WSCLIENT="$6"
23	# The ssh recipes a handoff leg drives name `mux` and let the remote's PATH	23	# The ssh recipes a handoff leg drives name `mux` and let the remote's PATH
24	# find it, so the build's own bin directory goes in front of the shims that	24	# find it, so the build's own bin directory goes in front of the shims that
25	# stand in for a remote. The client's LOCAL auto-start no longer reads PATH	25	# stand in for a remote. The client's LOCAL auto-start no longer reads PATH
26	# at all — it forks into this binary's own daemon (spawn.zig) — so a leg	26	# at all — it execs this same binary with argv `mux d run …` (spawn.zig) —
27	# that forgets its `mux d run &` can no longer silently grade an installed	27	# so a leg that forgets its `mux d run &` can no longer silently grade an
28	# release, which it did against a v0.0.1-10 with no agent code in it.	28	# installed release, which it did against a v0.0.1-10 with no agent code.
29	PATH="$(cd "$(dirname "$MUX")" && pwd):$PATH"	29	PATH="$(cd "$(dirname "$MUX")" && pwd):$PATH"
30	export PATH	30	export PATH
31		31