[metal] Reclaim base memory pages for later app use

ape/ape.S

@@ -1504,7 +1504,6 @@ long:	movabs	$BANE+PHYSICAL(0f),%rax
 	xor	%r15d,%r15d
 	xor	%ebx,%ebx
 	xor	%ebp,%ebp
-	push	%rbp
 	mov	$mm,%rdi
 	mov	%cr3,%rsi
 	mov	$IMAGE_BASE_PHYSICAL,%edx
@@ -1594,6 +1593,10 @@ kernel:	movabs	$ape_stack_vaddr,%rsp
 	.byte	0x0f,0x1f,0207			# nop rdi binbase
 	.long	(IMAGE_BASE_VIRTUAL-IMAGE_BASE_REAL)/512
 #endif
+	movabs	$BANE+mm,%rdi
+	mov	$0x79000,%esi
+	mov	$0x7f000,%edx
+	call	__reclaim_boot_pages
 	push	$_HOSTMETAL			# sets __hostos in crt.S
 	pop	%rcx
 	pushq	.Lenv0(%rip)			# envp[0][0]

libc/intrin/mman.greg.c

@@ -33,6 +33,7 @@
 │ αcτµαlly pδrταblε εxεcµταblε § no-frills virtual memory management           │
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "ape/relocations.h"
+#include "libc/assert.h"
 #include "libc/elf/def.h"
 #include "libc/elf/struct/phdr.h"
 #include "libc/macros.internal.h"
@@ -44,13 +45,25 @@
 
 #define INVERT(x) (BANE + PHYSICAL(x))
 
+struct ReclaimedPage {
+  uint64_t next;
+};
+
 /**
  * Allocates new page of physical memory.
  */
 noasan texthead uint64_t __new_page(struct mman *mm) {
-  uint64_t p;
+  uint64_t p = mm->frp;
+  if (p) {
+    uint64_t q;
+    struct ReclaimedPage *rp = (struct ReclaimedPage *)(BANE + p);
+    _unassert(p == (p & PAGE_TA));
+    q = rp->next;
+    _unassert(q == (q & PAGE_TA));
+    mm->frp = q;
+    return p;
+  }
   if (mm->pdpi == mm->e820n) {
-    /* TODO: reclaim free pages */
     return 0;
   }
   while (mm->pdp >= mm->e820[mm->pdpi].addr + mm->e820[mm->pdpi].size) {
@@ -113,6 +126,7 @@ static noasan textreal void __normalize_e820(struct mman *mm, uint64_t top) {
   mm->pdp = MAX(top, mm->e820[0].addr);
   mm->pdpi = 0;
   mm->e820n = n;
+  mm->frp = 0;
 }
 
 /**
@@ -210,3 +224,21 @@ noasan textreal void __map_phdrs(struct mman *mm, uint64_t *pml4t, uint64_t b,
   }
   mm->pdp = MAX(mm->pdp, m);
 }
+
+/**
+ * Reclaim memory pages which were used at boot time but which can now be
+ * made available for the application.
+ */
+noasan textreal void __reclaim_boot_pages(struct mman *mm, uint64_t skip_start,
+                                          uint64_t skip_end) {
+  uint64_t p = mm->frp, q = IMAGE_BASE_REAL, e;
+  e = mm->e820[0].addr + mm->e820[0].size;
+  while (q != e) {
+    struct ReclaimedPage *rp = (struct ReclaimedPage *)(BANE + q);
+    rp->next = p;
+    p = q;
+    q += 4096;
+    if (q == skip_start) q = skip_end;
+  }
+  mm->frp = p;
+}

libc/runtime/efimain.greg.c

@@ -136,6 +136,7 @@ __msabi noasan EFI_STATUS EfiMain(EFI_HANDLE ImageHandle,
   pml4t[0] = (intptr_t)pdpt1 + PAGE_V + PAGE_RW;
   pml4t[256] = (intptr_t)pdpt2 + PAGE_V + PAGE_RW;
   __map_phdrs(mm, pml4t, 1024 * 1024, 1024 * 1024 + (_end - _base));
+  __reclaim_boot_pages(mm, 0x79000, 0x7f000);
 
   /*
    * Asks UEFI to handover control?

libc/runtime/mman.internal.h

@@ -8,31 +8,33 @@ struct mman {
   int64_t pdp;                           /* 0x0500 */
   int32_t pdpi;                          /* 0x0508 */
   int32_t e820n;                         /* 0x050c */
-  struct SmapEntry e820[256];            /* 0x0510 */
+  uint64_t frp;                          /* 0x0510 — free list of reclaimed,
-  struct SmapEntry e820_end[0];          /* 0x1d10 */
+                                                     previously used pages */
-  char pc_drive_base_table[11];          /* 0x1d10 */
+  struct SmapEntry e820[256];            /* 0x0518 */
-  unsigned char pc_drive_type;           /* 0x1d1b */
+  struct SmapEntry e820_end[0];          /* 0x1d18 */
-  unsigned char pc_drive_last_sector;    /* 0x1d1c */
+  char pc_drive_base_table[11];          /* 0x1d18 */
-  unsigned short pc_drive_last_cylinder; /* 0x1d1e */
+  unsigned char pc_drive_type;           /* 0x1d23 */
-  unsigned char pc_drives_attached;      /* 0x1d20 */
+  unsigned char pc_drive_last_sector;    /* 0x1d24 */
-  unsigned char pc_drive_last_head;      /* 0x1d21 */
+  unsigned short pc_drive_last_cylinder; /* 0x1d26 */
-  unsigned char pc_drive;                /* 0x1d22 */
+  unsigned char pc_drives_attached;      /* 0x1d28 */
-  char bad_idt[6];                       /* 0x1d23 */
+  unsigned char pc_drive_last_head;      /* 0x1d29 */
-  unsigned char pc_video_type;           /* 0x1d29 */
+  unsigned char pc_drive;                /* 0x1d2a */
-  unsigned short pc_video_stride;        /* 0x1d2a — line width, including any
+  char bad_idt[6];                       /* 0x1d2b */
+  unsigned char pc_video_type;           /* 0x1d31 */
+  unsigned short pc_video_stride;        /* 0x1d32 — line width, including any
                                                      invisible "pixels" — in
                                                      bytes (NOTE) */
-  unsigned short pc_video_width;         /* 0x1d2c — width in chars. (text)
+  unsigned short pc_video_width;         /* 0x1d34 — width in chars. (text)
                                                      or pixels (graphics) */
-  unsigned short pc_video_height;        /* 0x1d2e — height in chars. (text)
+  unsigned short pc_video_height;        /* 0x1d36 — height in chars. (text)
                                                      or pixels (graphics) */
-  uint64_t pc_video_framebuffer;         /* 0x1d30 — physical address of
+  uint64_t pc_video_framebuffer;         /* 0x1d38 — physical address of
                                                      video frame buffer */
-  uint64_t pc_video_framebuffer_size;    /* 0x1d38 */
+  uint64_t pc_video_framebuffer_size;    /* 0x1d40 */
-  struct {                               /* 0x1d40 — starting cursor pos. */
+  struct {                               /* 0x1d48 — starting cursor pos. */
     unsigned short y, x;
   } pc_video_curs_info;
-  unsigned short pc_video_char_height;   /* 0x1d44 — character height (useful
+  unsigned short pc_video_char_height;   /* 0x1d4c — character height (useful
                                                      for setting cursor shape
                                                      in text mode) */
 };

libc/runtime/pc.internal.h

@@ -189,6 +189,7 @@ uint64_t __new_page(struct mman *);
 void __invert_memory_area(struct mman *, uint64_t *, uint64_t, uint64_t,
                           uint64_t);
 void __map_phdrs(struct mman *, uint64_t *, uint64_t, uint64_t);
+void __reclaim_boot_pages(struct mman *, uint64_t, uint64_t);
 
 forceinline unsigned char inb(unsigned short port) {
   unsigned char al;