Revert lguest magic and use hook in head.S

Version 2.07 of the boot protocol uses 0x23C for the hardware_subarch
field, that for lguest is "1".  This allows us to use the standard
boot entry point rather than the "GenuineLguest" string hack.

The standard entry point also clears the BSS and copies the boot parameters
and commandline for us, saving more code.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

1 files changed, 13 insertions, 29 deletions

diff --git a/Documentation/lguest/lguest.c b/Documentation/lguest/lguest.c
index cbf4becd266..004c5c6aba6 100644
--- a/Documentation/lguest/lguest.c
+++ b/Documentation/lguest/lguest.c
@@ -251,23 +251,6 @@ static void *get_pages(unsigned int num)
 	return addr;
 }
 
-/* To find out where to start we look for the magic Guest string, which marks
- * the code we see in lguest_asm.S.  This is a hack which we are currently
- * plotting to replace with the normal Linux entry point. */
-static unsigned long entry_point(const void *start, const void *end)
-{
-	const void *p;
-
-	/* The scan gives us the physical starting address.  We boot with
-	 * pagetables set up with virtual and physical the same, so that's
-	 * OK. */
-	for (p = start; p < end; p++)
-		if (memcmp(p, "GenuineLguest", strlen("GenuineLguest")) == 0)
-			return to_guest_phys(p + strlen("GenuineLguest"));
-
-	errx(1, "Is this image a genuine lguest?");
-}
-
 /* This routine is used to load the kernel or initrd.  It tries mmap, but if
  * that fails (Plan 9's kernel file isn't nicely aligned on page boundaries),
  * it falls back to reading the memory in. */
@@ -303,7 +286,6 @@ static void map_at(int fd, void *addr, unsigned long offset, unsigned long len)
  * We return the starting address. */
 static unsigned long map_elf(int elf_fd, const Elf32_Ehdr *ehdr)
 {
-	void *start = (void *)-1, *end = NULL;
 	Elf32_Phdr phdr[ehdr->e_phnum];
 	unsigned int i;
 
@@ -335,19 +317,13 @@ static unsigned long map_elf(int elf_fd, const Elf32_Ehdr *ehdr)
 		verbose("Section %i: size %i addr %p\n",
 			i, phdr[i].p_memsz, (void *)phdr[i].p_paddr);
 
-		/* We track the first and last address we mapped, so we can
-		 * tell entry_point() where to scan. */
-		if (from_guest_phys(phdr[i].p_paddr) < start)
-			start = from_guest_phys(phdr[i].p_paddr);
-		if (from_guest_phys(phdr[i].p_paddr) + phdr[i].p_filesz > end)
-			end=from_guest_phys(phdr[i].p_paddr)+phdr[i].p_filesz;
-
 		/* We map this section of the file at its physical address. */
 		map_at(elf_fd, from_guest_phys(phdr[i].p_paddr),
 		       phdr[i].p_offset, phdr[i].p_filesz);
 	}
 
-	return entry_point(start, end);
+	/* The entry point is given in the ELF header. */
+	return ehdr->e_entry;
 }
 
 /*L:160 Unfortunately the entire ELF image isn't compressed: the segments
@@ -374,7 +350,8 @@ static unsigned long unpack_bzimage(int fd)
 
 	verbose("Unpacked size %i addr %p\n", len, img);
 
-	return entry_point(img, img + len);
+	/* The entry point for a bzImage is always the first byte */
+	return (unsigned long)img;
 }
 
 /*L:150 A bzImage, unlike an ELF file, is not meant to be loaded.  You're
@@ -1684,8 +1661,15 @@ int main(int argc, char *argv[])
 	*(u32 *)(boot + 0x228) = 4096;
 	concat(boot + 4096, argv+optind+2);
 
-	/* The guest type value of "1" tells the Guest it's under lguest. */
-	*(int *)(boot + 0x23c) = 1;
+	/* Boot protocol version: 2.07 supports the fields for lguest. */
+	*(u16 *)(boot + 0x206) = 0x207;
+
+	/* The hardware_subarch value of "1" tells the Guest it's an lguest. */
+	*(u32 *)(boot + 0x23c) = 1;
+
+	/* Set bit 6 of the loadflags (aka. KEEP_SEGMENTS) so the entry path
+	 * does not try to reload segment registers. */
+	*(u8 *)(boot + 0x211) |= (1 << 6);
 
 	/* We tell the kernel to initialize the Guest: this returns the open
 	 * /dev/lguest file descriptor. */