acpi: uACPI, for interrupt routing, the power button and power-off

The firmware's AML is now interpreted. uACPI 6.1.1 (MIT) is fetched by
ports/uacpi, checksum-verified, and compiled into the kernel unmodified,
the same way lwIP is. kernel/acpi/host.c is its host layer: memory,
mapping, port and PCI config I/O, time, mutexes and events that spin
before the scheduler exists, the SCI, and an "acpi" thread for the
work the SCI defers.

PCI interrupts go where the board says. pci_init() now routes every
device's INTx through the root bridge's _PRT before drivers bind. It
follows link devices' _CRS, uses a bridge's own _PRT where the namespace
has one, and swizzles through bridges that don't. Before this, INTx
waited on the 8259's line number, which is the wrong pin in APIC mode.
irq_register() takes a trigger mode rather than a level/low flag,
because q35's links and most SCIs are level, active-high. The MADT's
interrupt source overrides are now parsed, and are what places the SCI.

The power button syncs the filesystems and powers off. shutdown() and
reboot() go through the firmware's S5 and reset register first, and
only then fall back to the emulators' ports, which a real board does
not answer.

Tested under QEMU: q35 with MSI off routes xHCI to GSI 22,
level/active-high, and it takes real interrupts with nothing polled.
system_powerdown powers off q35 and i440fx (QEMU exits 0), and q35
with 4 CPUs boots from NVMe with USB hot-plug working alongside.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S1giNvrHTrPMPw7V6x1kQ4

Makefile

@@ -88,6 +88,18 @@ KERN_NET += $(addprefix $(BUILD)/lwip/core/ipv4/, \
 KERN_NET += $(addprefix $(BUILD)/lwip/netif/, ethernet.o)
 KERN_NET += $(addprefix $(BUILD)/kernel/net/lwip/, sys_arch.o netif_eth.o)
 
+# uACPI: the AML interpreter, MIT, unpacked by ports/uacpi into
+# build/ports/uacpi/src and compiled into the kernel like lwIP. kernel/acpi/
+# is the host side of it -- memory, locks, I/O, the SCI -- and what the kernel
+# uses it for: PCI interrupt routing, the power button and S5.
+UACPIDIR  = $(BUILD)/ports/uacpi/src
+KERN_ACPI = $(addprefix $(BUILD)/uacpi/, \
+              default_handlers.o event.o interpreter.o io.o mutex.o \
+              namespace.o notify.o opcodes.o opregion.o osi.o registers.o \
+              resources.o shareable.o sleep.o stdlib.o tables.o types.o \
+              uacpi.o utilities.o)
+KERN_ACPI += $(addprefix $(BUILD)/kernel/acpi/, host.o aml.o)
+
 KERN_PROC = $(addprefix $(BUILD)/kernel/proc/, \
               proc.o)
 
@@ -99,7 +111,7 @@ KERN_SYS  = $(addprefix $(BUILD)/kernel/sys/, \
 KERN_ARCH += $(BUILD)/kernel/arch/x86_64/vectors.o
 
 KERNOBJS = $(KERN_ARCH) $(KERN_CORE) $(KERN_DEV) $(KERN_DRIVERS) \
-           $(KERN_FS) $(KERN_NET) $(KERN_PROC) $(KERN_SYS)
+           $(KERN_FS) $(KERN_NET) $(KERN_ACPI) $(KERN_PROC) $(KERN_SYS)
 # entry.o must be first in link order; remove it from KERNOBJS for the rule
 KERN_NOENTRY = $(filter-out $(BUILD)/kernel/arch/x86_64/entry.o, $(KERNOBJS))
 
@@ -942,6 +954,33 @@ $(BUILD)/lwip/%.o: $(LWIPDIR)/%.c | $(LWIPDIR)
 $(LWIPDIR):
 	$(MAKE) -C ports lwip
 
+# uACPI's headers for its own files and for kernel/acpi/, and the same
+# configuration for both: a define seen by one side and not the other changes
+# the size of structures they pass between them. Builtin string functions,
+# because the kernel's memcpy and friends are not declared the way <string.h>
+# declares them.
+UACPI_CFLAGS = -I$(UACPIDIR)/include -DUACPI_USE_BUILTIN_STRING
+# Third-party, warned about differently from this tree; silenced for its files
+# only. kernel/acpi/ is ours and is held to the usual warnings.
+UACPI_QUIET  = -Wno-unused-parameter -Wno-sign-compare -Wno-unused-function
+
+$(BUILD)/kernel/acpi/%.o: kernel/acpi/%.c | $(UACPIDIR)
+	@mkdir -p $(BUILD)/kernel/acpi
+	$(CC) $(CFLAGS) $(UACPI_CFLAGS) -c $< -o $@
+
+$(BUILD)/uacpi/%.o: $(UACPIDIR)/source/%.c | $(UACPIDIR)
+	@mkdir -p $(dir $@)
+	$(CC) $(CFLAGS) $(UACPI_CFLAGS) $(UACPI_QUIET) -c $< -o $@
+
+$(UACPIDIR):
+	$(MAKE) -C ports uacpi
+
+# The sources exist once the tarball is unpacked. Saying so is what lets the
+# pattern rule above apply on a fresh tree, where make would otherwise look
+# for $(UACPIDIR)/source/foo.c, find nothing, and report no rule for foo.o.
+$(patsubst $(BUILD)/uacpi/%.o,$(UACPIDIR)/source/%.c,$(filter $(BUILD)/uacpi/%,$(KERN_ACPI))): | $(UACPIDIR)
+	@:
+
 $(BUILD)/kernel/proc/%.o: kernel/proc/%.c
 	@mkdir -p $(BUILD)/kernel/proc
 	$(CC) $(CFLAGS) -c $< -o $@