arch: ppc32 + riscv32 PAGE_OFFSET_INVARIANT=1 — unlock coupling synth

Same shape as the prior loongarch64 activation: PAGE_OFFSET on both
arches is a single compile-time constant (0xc0000000) with no VMSPLIT
or paging-mode runtime dependency within KASLD's modelled scope, so
Q_PAGE_OFFSET is pinnable without evidence. page_offset_invariant_pin
fires and text_base_coupling_synth propagates Q_VIRT_TEXT_BASE ↔
Q_PHYS_TEXT_BASE. ppc32 cross-test PASS; host 280/280.

Author: bcoles

src/include/kasld/arch/loongarch64.h

@@ -36,6 +36,14 @@
 // Directmap leaks cannot reveal the KASLR slide.
 #define PAGE_OFFSET_RANDOMIZED 0
 
+// The compile-time PAGE_OFFSET is the architectural guaranteed runtime
+// value: the kernel writes _ULCAST_(0x9) to the DMW1 CSR unconditionally
+// at boot, so Q_PAGE_OFFSET can be pinned without evidence — same
+// "architectural certainty" shape as MIPS CKSEG0 and ppc64 book3s.
+// Unlocks text_base_coupling_synth (it needs Q_PAGE_OFFSET pinned to
+// propagate Q_VIRT_TEXT_BASE ↔ Q_PHYS_TEXT_BASE).
+#define PAGE_OFFSET_INVARIANT 1
+
 // XKPRANGE starts at 0x8000000000000000 (hardware direct map windows DMW0/1/2).
 // XKVRANGE starts at 0xc000000000000000 (vmalloc, modules, vmemmap).
 // XSPRANGE (0x4000000000000000) is hardware-accessible at PLV0 but unused by

src/include/kasld/arch/ppc32.h

@@ -23,10 +23,14 @@
 
 // PAGE_OFFSET and PHYS_OFFSET are compile-time on ppc32 (BookE
 // CONFIG_RELOCATABLE is out of KASLD scope). Mainline ppc32 has no KASLR —
-// text sits at a fixed offset within the linear map.
+// text sits at a fixed offset within the linear map. The compile-time
+// constant is the architectural guaranteed runtime value within KASLD's
+// modelled scope, so Q_PAGE_OFFSET is pinnable without evidence (same
+// shape as mips32/64 and ppc64). Unlocks text_base_coupling_synth.
 // https://elixir.bootlin.com/linux/v6.1.1/source/arch/powerpc/include/asm/page.h#L240
 #define DIRECTMAP_STATIC 1
 #define TEXT_TRACKS_DIRECTMAP 1
+#define PAGE_OFFSET_INVARIANT 1
 
 #define KERNEL_VIRT_VAS_START PAGE_OFFSET
 #define KERNEL_VIRT_VAS_END 0xfffffffful

src/include/kasld/arch/riscv32.h

@@ -22,9 +22,13 @@
 #define PHYS_OFFSET 0ul
 // PAGE_OFFSET and PHYS_OFFSET are compile-time on riscv32; the directmap
 // projection is sound. No mainline KASLR — text sits at a fixed offset
-// within the linear map.
+// within the linear map. The compile-time constant is the architectural
+// guaranteed runtime value (no VMSPLIT/SATP/paging-mode dependency on
+// riscv32), so Q_PAGE_OFFSET is pinnable without evidence — same shape
+// as mips32/64 and ppc32/64. Unlocks text_base_coupling_synth.
 #define DIRECTMAP_STATIC 1
 #define TEXT_TRACKS_DIRECTMAP 1
+#define PAGE_OFFSET_INVARIANT 1
 
 #define KERNEL_VIRT_VAS_START PAGE_OFFSET
 #define KERNEL_VIRT_VAS_END 0xfffffffful