[PATCH] ldso: use _dl_pagesize for library-loading addresses and offsets

[Jeremy Kerr]

Some powerpc machines can support 64k pages, enabled by the
CONFIG_64K_PAGES option in linux.

However, the uClibc dynamic loader won't currently work on these
machines, as it uses hard-coded values (PAGE_ALIGN, ADDR_ALIGN and
OFFS_ALIGN) in the ldso architecture-specific headers.  When running on
a kernel with 64k pages, ld.so tries to mmap with 4k-aligned addresses,
rather than 64k, so mmap fails with -EINVAL.

When booting a 64k machine with a uClibc dynamic linker, init fails
with:

/init:500: can't map '/lib/libc.so.0'
/init:500: can't map '/lib/libc.so.0'
/init:500: can't map '/lib/libc.so.0'
/init: can't load library 'libc.so.0'
Kernel panic - not syncing: Attempted to kill init!

This change allows ld.so determine these alignment masks at runtime,
rather than compile-time. Since we have the _dl_pagesize variable
available, we can use that to generate the appropriate masks.

This allows me to start a uClibc-based root fs on a 64k machine.

Signed-off-by: Jeremy Kerr <jk at ozlabs.org>

---

 ldso/ldso/dl-elf.c |   39 ++++++++++++++++++++++-----------------
 1 file changed, 22 insertions(+), 17 deletions(-)

Index: uClibc/ldso/ldso/dl-elf.c
===================================================================
--- uClibc.orig/ldso/ldso/dl-elf.c	2008-11-25 20:19:19.000000000 +1100
+++ uClibc/ldso/ldso/dl-elf.c	2008-11-25 20:22:26.000000000 +1100
@@ -336,6 +336,7 @@ struct elf_resolve *_dl_load_elf_shared_
 	unsigned long dynamic_info[DYNAMIC_SIZE];
 	unsigned long *lpnt;
 	unsigned long libaddr;
+	unsigned long page_align, addr_align, offs_align;
 	unsigned long minvma = 0xffffffff, maxvma = 0;
 	int i, flags, piclib, infile;
 	ElfW(Addr) relro_addr = 0;
@@ -442,7 +443,11 @@ struct elf_resolve *_dl_load_elf_shared_
 
 	DL_CHECK_LIB_TYPE (epnt, piclib, _dl_progname, libname);
 
-	maxvma = (maxvma + ADDR_ALIGN) & ~ADDR_ALIGN;
+	addr_align = _dl_pagesize - 1;
+	page_align = ~addr_align;
+	offs_align = page_align & ~(1 << 31);
+
+	maxvma = (maxvma + addr_align) & ~addr_align;
 	minvma = minvma & ~0xffffU;
 
 	flags = MAP_PRIVATE /*| MAP_DENYWRITE */ ;
@@ -517,15 +522,15 @@ struct elf_resolve *_dl_load_elf_shared_
 				       aligned pages:
 
 				    ((ppnt->p_vaddr + ppnt->p_filesz
-				      + ADDR_ALIGN)
-				     & PAGE_ALIGN)
+				      + addr_align)
+				     & page_align)
 				    < ppnt->p_vaddr + ppnt->p_memsz)
 
 				       Instead, we have to do this:  */
 				    ppnt->p_filesz < ppnt->p_memsz)
 				  {
 				    piclib2map = (char *)
-				      _dl_mmap(0, (ppnt->p_vaddr & ADDR_ALIGN)
+				      _dl_mmap(0, (ppnt->p_vaddr & addr_align)
 					       + ppnt->p_memsz,
 					       LXFLAGS(ppnt->p_flags),
 					       flags | MAP_ANONYMOUS, -1, 0);
@@ -533,14 +538,14 @@ struct elf_resolve *_dl_load_elf_shared_
 				      goto cant_map;
 				    DL_INIT_LOADADDR_HDR
 				      (lib_loadaddr, piclib2map
-				       + (ppnt->p_vaddr & ADDR_ALIGN), ppnt);
+				       + (ppnt->p_vaddr & addr_align), ppnt);
 				  }
 
 				tryaddr = piclib == 2 ? piclib2map
 				  : ((char*) (piclib ? libaddr : 0) +
-				     (ppnt->p_vaddr & PAGE_ALIGN));
+				     (ppnt->p_vaddr & page_align));
 
-				size = (ppnt->p_vaddr & ADDR_ALIGN)
+				size = (ppnt->p_vaddr & addr_align)
 				  + ppnt->p_filesz;
 
 				/* For !MMU, mmap to fixed address will fail.
@@ -553,7 +558,7 @@ struct elf_resolve *_dl_load_elf_shared_
 				  status = (char *) _dl_mmap
 				    (tryaddr, size, LXFLAGS(ppnt->p_flags),
 				     flags | (piclib2map ? MAP_FIXED : 0),
-				     infile, ppnt->p_offset & OFFS_ALIGN);
+				     infile, ppnt->p_offset & offs_align);
 #ifndef __ARCH_USE_MMU__
 				else
 				  status = MAP_FAILED;
@@ -561,7 +566,7 @@ struct elf_resolve *_dl_load_elf_shared_
 #ifdef _DL_PREAD
 				if (_dl_mmap_check_error(status) && piclib2map
 				    && (_DL_PREAD (infile, tryaddr, size,
-						   ppnt->p_offset & OFFS_ALIGN)
+						   ppnt->p_offset & offs_align)
 					== size))
 				  status = tryaddr;
 #endif
@@ -580,7 +585,7 @@ struct elf_resolve *_dl_load_elf_shared_
 				if (! piclib2map) {
 				  DL_INIT_LOADADDR_HDR
 				    (lib_loadaddr, status
-				     + (ppnt->p_vaddr & ADDR_ALIGN), ppnt);
+				     + (ppnt->p_vaddr & addr_align), ppnt);
 				}
 				/* Now we want to allocate and
 				   zero-out any data from the end of
@@ -608,7 +613,7 @@ struct elf_resolve *_dl_load_elf_shared_
 				/* MAP_SIZE is the address of the
 				   beginning of the next page.  */
 				map_size = (ppnt->p_vaddr + ppnt->p_filesz
-					    + ADDR_ALIGN) & PAGE_ALIGN;
+					    + addr_align) & page_align;
 
 #ifndef MIN
 # define MIN(a,b) ((a) < (b) ? (a) : (b))
@@ -632,20 +637,20 @@ struct elf_resolve *_dl_load_elf_shared_
 				}
 			} else {
 				tryaddr = (piclib == 2 ? 0
-					   : (char *) (ppnt->p_vaddr & PAGE_ALIGN)
+					   : (char *) (ppnt->p_vaddr & page_align)
 					   + (piclib ? libaddr : 0));
-				size = (ppnt->p_vaddr & ADDR_ALIGN) + ppnt->p_filesz;
+				size = (ppnt->p_vaddr & addr_align) + ppnt->p_filesz;
 				status = (char *) _dl_mmap
 					   (tryaddr, size, LXFLAGS(ppnt->p_flags),
 					    flags | (piclib == 2 ? MAP_EXECUTABLE
 						     | MAP_DENYWRITE : 0),
-					    infile, ppnt->p_offset & OFFS_ALIGN);
+					    infile, ppnt->p_offset & offs_align);
 				if (_dl_mmap_check_error(status)
 				    || (tryaddr && tryaddr != status))
 				  goto cant_map;
 				DL_INIT_LOADADDR_HDR
 				  (lib_loadaddr, status
-				   + (ppnt->p_vaddr & ADDR_ALIGN), ppnt);
+				   + (ppnt->p_vaddr & addr_align), ppnt);
 			}
 
 			/* if (libaddr == 0 && piclib) {
@@ -690,8 +695,8 @@ struct elf_resolve *_dl_load_elf_shared_
 		for (i = 0; i < epnt->e_phnum; i++, ppnt++) {
 			if (ppnt->p_type == PT_LOAD && !(ppnt->p_flags & PF_W))
 				_dl_mprotect((void *) ((piclib ? libaddr : 0) +
-							(ppnt->p_vaddr & PAGE_ALIGN)),
-						(ppnt->p_vaddr & ADDR_ALIGN) + (unsigned long) ppnt->p_filesz,
+							(ppnt->p_vaddr & page_align)),
+						(ppnt->p_vaddr & addr_align) + (unsigned long) ppnt->p_filesz,
 						PROT_READ | PROT_WRITE | PROT_EXEC);
 		}
 #else