components: gate CONFIG_PAGE_OFFSET page_offset pin on PAGE_OFFSET_FROM_CONFIG

boot_config and proc_config emitted CONFIG_PAGE_OFFSET as a REGION_PAGE_OFFSET
base record, which page_offset_from_landmark pins to Q_PAGE_OFFSET via
C_EQUALS — with no arch gate. CONFIG_PAGE_OFFSET equals the runtime
page_offset only on PAGE_OFFSET_FROM_CONFIG arches (x86_32, arm32); on any
arch whose CONFIG_PAGE_OFFSET differs from the running base, that pin would
exclude the truth. (Latent today only because ppc, the one supported arch in
that bucket, is PAGE_OFFSET_INVARIANT.)

Gate both emissions on PAGE_OFFSET_FROM_CONFIG, mirroring the scalar path
(bootconfig_facts -> page_offset_from_config). Gating, not removing:
proc_config's /proc/config.gz is a source the scalar path does not read.
Mark get_kconfig_page_offset __attribute__((unused)) since its call sites are
now conditional.

Author: bcoles

src/components/boot_config.c

@@ -88,13 +88,20 @@ int main(void) {
   if (open_boot_config(&fp) < 0)
     return KASLD_EXIT_UNAVAILABLE;
 
-  /* Detect PAGE_OFFSET (32-bit vmsplit) */
+#if PAGE_OFFSET_FROM_CONFIG
+  /* Detect PAGE_OFFSET (32-bit vmsplit). CONFIG_PAGE_OFFSET equals the runtime
+   * page_offset only on PAGE_OFFSET_FROM_CONFIG arches (x86_32, arm32); pinning
+   * Q_PAGE_OFFSET to it via page_offset_from_landmark's C_EQUALS would exclude
+   * the truth on arches whose CONFIG_PAGE_OFFSET differs from the running base.
+   * (The properly gated scalar path is bootconfig_facts ->
+   * page_offset_from_config.) */
   unsigned long virt_page_offset = get_kconfig_page_offset(fp);
   if (virt_page_offset) {
     kasld_info("CONFIG_PAGE_OFFSET: %#lx", virt_page_offset);
     kasld_result_base(KASLD_TYPE_VIRT, REGION_PAGE_OFFSET, virt_page_offset,
                       NULL, CONF_PARSED);
   }
+#endif
 
   /* CONFIG_PHYSICAL_START (x86 LOAD_PHYSICAL_ADDR). The honest-top floors
    * for Q_VIRT_IMAGE_BASE / Q_PHYS_IMAGE_BASE are *widened* to the smallest

src/components/proc_config.c

@@ -140,13 +140,20 @@ int main(void) {
   if (!fp)
     return KASLD_EXIT_UNAVAILABLE;
 
-  /* Detect PAGE_OFFSET (32-bit vmsplit) */
+#if PAGE_OFFSET_FROM_CONFIG
+  /* Detect PAGE_OFFSET (32-bit vmsplit). CONFIG_PAGE_OFFSET equals the runtime
+   * page_offset only on PAGE_OFFSET_FROM_CONFIG arches (x86_32, arm32); pinning
+   * Q_PAGE_OFFSET to it via page_offset_from_landmark's C_EQUALS would exclude
+   * the truth on arches whose CONFIG_PAGE_OFFSET differs from the running base.
+   * (The properly gated scalar path is bootconfig_facts ->
+   * page_offset_from_config.) */
   unsigned long virt_page_offset = get_kconfig_page_offset(fp);
   if (virt_page_offset) {
     kasld_info("CONFIG_PAGE_OFFSET: %#lx", virt_page_offset);
     kasld_result_base(KASLD_TYPE_VIRT, REGION_PAGE_OFFSET, virt_page_offset,
                       NULL, CONF_PARSED);
   }
+#endif
 
   /* CONFIG_PHYSICAL_START (x86 LOAD_PHYSICAL_ADDR) — see boot_config.c. */
   unsigned long phys_start = get_kconfig_physical_start(fp);

src/include/kconfig.h

@@ -38,8 +38,10 @@ static int is_kconfig_set(FILE *fp, const char *config) {
 
 /* Search for CONFIG_PAGE_OFFSET=0x... in the kernel config.
  * Falls back to CONFIG_VMSPLIT_* choices (x86_32, arm32).
- * Returns the value, or 0 if not found. */
-static unsigned long get_kconfig_page_offset(FILE *fp) {
+ * Returns the value, or 0 if not found.
+ * __attribute__((unused)): callers gate use on PAGE_OFFSET_FROM_CONFIG, so this
+ * is unreferenced on arches where CONFIG_PAGE_OFFSET != runtime page_offset. */
+__attribute__((unused)) static unsigned long get_kconfig_page_offset(FILE *fp) {
   const char *key = "CONFIG_PAGE_OFFSET=";
   size_t keylen = strlen(key);
   char buf[BUFSIZ];