[PATCH] uml: fix static binary segfault

When UML is built as a static binary, it segfaults when run.  The reason is
that a memory hole that is present in dynamic binaries isn't there in static
binaries, and it contains essential stuff.

This fix removes the code which maps some anonymous memory into that hole and
cleans up some related code.

Signed-off-by: Jeff Dike <jdike@addtoit.com>
Cc: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/um/kernel/mem.c

@@ -24,8 +24,6 @@
 #include "init.h"
 #include "kern_constants.h"
 
-extern char __binary_start;
-
 /* Changed during early boot */
 unsigned long *empty_zero_page = NULL;
 unsigned long *empty_bad_page = NULL;
@@ -65,8 +63,6 @@ static void setup_highmem(unsigned long highmem_start,
 
 void mem_init(void)
 {
-	unsigned long start;
-
 	max_low_pfn = (high_physmem - uml_physmem) >> PAGE_SHIFT;
 
         /* clear the zero-page */
@@ -81,13 +77,6 @@ void mem_init(void)
 	free_bootmem(__pa(brk_end), uml_reserved - brk_end);
 	uml_reserved = brk_end;
 
-	/* Fill in any hole at the start of the binary */
-	start = (unsigned long) &__binary_start & PAGE_MASK;
-	if(uml_physmem != start){
-		map_memory(uml_physmem, __pa(uml_physmem), start - uml_physmem,
-			   1, 1, 0);
-	}
-
 	/* this will put all low memory onto the freelists */
 	totalram_pages = free_all_bootmem();
 	totalhigh_pages = highmem >> PAGE_SHIFT;

arch/um/kernel/physmem.c

@@ -317,7 +317,7 @@ void map_memory(unsigned long virt, unsigned long phys, unsigned long len,
 	}
 }
 
-extern int __syscall_stub_start, __binary_start;
+extern int __syscall_stub_start;
 
 void setup_physmem(unsigned long start, unsigned long reserve_end,
 		   unsigned long len, unsigned long long highmem)

arch/um/kernel/skas/mem.c

@@ -9,20 +9,19 @@
 #include "mem_user.h"
 #include "skas.h"
 
-unsigned long set_task_sizes_skas(unsigned long *host_size_out,
-				  unsigned long *task_size_out)
+unsigned long set_task_sizes_skas(unsigned long *task_size_out)
 {
 	/* Round up to the nearest 4M */
-	unsigned long top = ROUND_4M((unsigned long) &host_size_out);
+	unsigned long host_task_size = ROUND_4M((unsigned long)
+						&host_task_size);
 
 #ifdef CONFIG_HOST_TASK_SIZE
 	*host_size_out = ROUND_4M(CONFIG_HOST_TASK_SIZE);
 	*task_size_out = CONFIG_HOST_TASK_SIZE;
 #else
-	*host_size_out = top;
 	if (!skas_needs_stub)
-		*task_size_out = top;
+		*task_size_out = host_task_size;
 	else *task_size_out = CONFIG_STUB_START & PGDIR_MASK;
 #endif
-	return ((unsigned long) set_task_sizes_skas) & ~0xffffff;
+	return host_task_size;
 }

arch/um/kernel/tt/mem.c

@@ -24,11 +24,13 @@ void before_mem_tt(unsigned long brk_start)
 #define SIZE ((CONFIG_NEST_LEVEL + CONFIG_KERNEL_HALF_GIGS) * 0x20000000)
 #define START (CONFIG_TOP_ADDR - SIZE)
 
-unsigned long set_task_sizes_tt(unsigned long *host_size_out,
-				unsigned long *task_size_out)
+unsigned long set_task_sizes_tt(unsigned long *task_size_out)
 {
+	unsigned long host_task_size;
+
 	/* Round up to the nearest 4M */
-	*host_size_out = ROUND_4M((unsigned long) &host_size_out);
+	host_task_size = ROUND_4M((unsigned long) &host_task_size);
 	*task_size_out = START;
-	return START;
+
+	return host_task_size;
 }

arch/um/kernel/um_arch.c

@@ -330,6 +330,8 @@ EXPORT_SYMBOL(end_iomem);
 
 #define MIN_VMALLOC (32 * 1024 * 1024)
 
+extern char __binary_start;
+
 int linux_main(int argc, char **argv)
 {
 	unsigned long avail, diff;
@@ -374,8 +376,9 @@ int linux_main(int argc, char **argv)
 
 	printf("UML running in %s mode\n", mode);
 
-	uml_start = CHOOSE_MODE_PROC(set_task_sizes_tt, set_task_sizes_skas,
-				     &host_task_size, &task_size);
+	uml_start = (unsigned long) &__binary_start;
+	host_task_size = CHOOSE_MODE_PROC(set_task_sizes_tt,
+					  set_task_sizes_skas, &task_size);
 
 	/*
  	 * Setting up handlers to 'sig_info' struct
@@ -395,7 +398,7 @@ int linux_main(int argc, char **argv)
 		physmem_size += UML_ROUND_UP(brk_start) - UML_ROUND_UP(&_end);
 	}
 
-	uml_physmem = uml_start;
+	uml_physmem = uml_start & PAGE_MASK;
 
 	/* Reserve up to 4M after the current brk */
 	uml_reserved = ROUND_4M(brk_start) + (1 << 22);

arch/um/kernel/uml.lds.S

@@ -7,13 +7,16 @@ jiffies = jiffies_64;
 
 SECTIONS
 {
-  /*This must contain the right address - not quite the default ELF one.*/
+  /* This must contain the right address - not quite the default ELF one.*/
   PROVIDE (__executable_start = START);
-  . = START + SIZEOF_HEADERS;
+  /* Static binaries stick stuff here, like the sigreturn trampoline,
+   * invisibly to objdump.  So, just make __binary_start equal to the very
+   * beginning of the executable, and if there are unmapped pages after this,
+   * they are forever unusable.
+   */
+  __binary_start = START;
 
-  /* Used in arch/um/kernel/mem.c. Any memory between START and __binary_start
-   * is remapped.*/
-  __binary_start = .;
+  . = START + SIZEOF_HEADERS;
 
 #ifdef MODE_TT
   .remap_data : { UNMAP_PATH (.data .bss) }