Fix handling of ELF segments with zero filesize

[David Gibson <david@gibson.dropbear.id.au>]

Andrew, please apply

mmap() returns -EINVAL if given a zero length, and thus elf_map() in
binfmt_elf.c does likewise if it attempts to map a (page-aligned) ELF
segment with zero filesize.  Such a situation never arises with the
default linker scripts, but there's nothing inherently wrong with
zero-filesize (but non-zero memsize) ELF segments.  Custom linker
scripts can generate them, and the kernel should be able to map them;
this patch makes it so.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

Index: working-2.6/fs/binfmt_elf.c
===================================================================
--- working-2.6.orig/fs/binfmt_elf.c	2005-11-23 15:56:30.000000000 +1100
+++ working-2.6/fs/binfmt_elf.c	2005-12-01 11:11:01.000000000 +1100
@@ -288,11 +288,17 @@ static unsigned long elf_map(struct file
 			struct elf_phdr *eppnt, int prot, int type)
 {
 	unsigned long map_addr;
+	unsigned long pageoffset = ELF_PAGEOFFSET(eppnt->p_vaddr);
 
 	down_write(&current->mm->mmap_sem);
-	map_addr = do_mmap(filep, ELF_PAGESTART(addr),
-			   eppnt->p_filesz + ELF_PAGEOFFSET(eppnt->p_vaddr), prot, type,
-			   eppnt->p_offset - ELF_PAGEOFFSET(eppnt->p_vaddr));
+	/* mmap() will return -EINVAL if given a zero size, but a
+	 * segment with zero filesize is perfectly valid */
+	if (eppnt->p_filesz + pageoffset)
+		map_addr = do_mmap(filep, ELF_PAGESTART(addr),
+				   eppnt->p_filesz + pageoffset, prot, type,
+				   eppnt->p_offset - pageoffset);
+	else
+		map_addr = ELF_PAGESTART(addr);
 	up_write(&current->mm->mmap_sem);
 	return(map_addr);
 }

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson