bootrm: allow entering with IF=1; smarter stub location

Change the stub location algorithm to prefer low memory above
0x800; above 0x510 if that is unavailable.  Also add the ability
to invoke the real-mode code with IF=1 if so is desired.

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

diff --git a/com32/include/syslinux/bootrm.h b/com32/include/syslinux/bootrm.h
index 66bdbbd..9cad0ca 100644 (file)
--- a/com32/include/syslinux/bootrm.h
+++ b/com32/include/syslinux/bootrm.h
@@ -35,6 +35,7 @@
 #define _SYSLINUX_BOOTRM_H
 
 #include <stdint.h>
+#include <stdbool.h>
 #include <com32.h>
 #include <syslinux/movebits.h>
 
@@ -60,6 +61,8 @@ struct syslinux_rm_regs {
 
   uint16_t ip;                 /* Offset 44 */
   uint16_t cs;                 /* Offset 46 */
+
+  bool sti;                    /* Offset 48 */
 };
 
 int syslinux_shuffle_boot_rm(struct syslinux_movelist *fraglist,

diff --git a/com32/lib/syslinux/shuffle_rm.c b/com32/lib/syslinux/shuffle_rm.c
index 4f424f3..3ef8de7 100644 (file)
--- a/com32/lib/syslinux/shuffle_rm.c
+++ b/com32/lib/syslinux/shuffle_rm.c
@@ -44,47 +44,45 @@ int syslinux_shuffle_boot_rm(struct syslinux_movelist *fraglist,
                             uint16_t bootflags,
                             struct syslinux_rm_regs *regs)
 {
-  int nd;
-  com32sys_t ireg;
-  char *regbuf;
   const struct syslinux_rm_regs_alt {
     uint16_t seg[6];
     uint32_t gpr[8];
     uint32_t csip;
+    bool sti;
   } *rp;
   int i, rv;
-  uint8_t handoff_code[5*5+8*6+5], *p;
-  struct syslinux_memmap *tmap, *tp;
-  addr_t regstub;
+  uint8_t handoff_code[5*5+8*6+1+5], *p;
+  struct syslinux_memmap *tmap;
+  addr_t regstub, stublen;
 
   tmap = syslinux_target_memmap(fraglist, memmap);
   if (!tmap)
     return -1;
 
   /* Search for a good place to put the real-mode register stub.
-     We prefer to put it as high as possible in the low 640K. */
-  regstub = 0;
-  for (tp = tmap; tp->type != SMT_END; tp = tp->next) {
-    addr_t xend, xlen;
-    if (tp->start >= 640*1024)
-      continue;
-    if (tp->type != SMT_FREE)
-      continue;
-    xend = tp->next->start;
-    if (xend > 640*1024)
-      xend = 640*1024;
-    xlen = xend - tp->start;
-    if (xlen < sizeof handoff_code)
-      continue;
-    regstub = xend - sizeof handoff_code; /* Best alternative so far */
+     We prefer it as low as possible above 0x800. */
+  regstub = 0x800;
+  stublen = sizeof handoff_code;
+  rv = syslinux_memmap_find(tmap, SMT_FREE, &regstub, &stublen);
+
+  if (rv || (regstub > 0x100000 - sizeof handoff_code)) {
+    /*
+     * Uh-oh.  This isn't real-mode accessible memory.
+     * It might be possible to do something insane here like
+     * putting the stub in the IRQ vectors, or in the 0x5xx segment.
+     * This code tries the 0x510-0x7ff range and hopes for the best.
+     */
+    regstub = 0x510;           /* Try the 0x5xx segment... */
+    stublen = sizeof handoff_code;
+    rv = syslinux_memmap_find(tmap, SMT_FREE, &regstub, &stublen);
+
+    if (!rv && (regstub > 0x100000 - sizeof handoff_code))
+      rv = -1;                 /* No acceptable memory found */
   }
 
   syslinux_free_memmap(tmap);
-
-  /* XXX: it might be possible to do something insane here like
-     putting the stub in the IRQ vectors... */
-  if (!regstub)
-    return -1;                 /* No space at all */
+  if (rv)
+    return -1;
 
   /* Build register-setting stub */
   p = handoff_code;
@@ -103,6 +101,8 @@ int syslinux_shuffle_boot_rm(struct syslinux_movelist *fraglist,
     *(uint32_t *)(p+2) = rp->gpr[i];
     p += 6;
   }
+  *p++ = rp->sti ? 0xfb : 0xfa;        /* STI/CLI */
+
   *p++ = 0xea;                 /* JMP FAR */
   *(uint32_t *)p = rp->csip;