Re: [Valgrind-users] Re: [uml-devel] Re: UML and valgrind

[Jeff Dike <jdike@addtoit.com>]

If you get past the clone and repe problems in valgrind, there was another
where V was confused by UML's stack switching.  I didn't see a patch for that
in my email, but someone special-cased longjmp in the stack overflow detection
to get around that.

IIRC, that got UML booting.  Now, it produced almost no useful information 
because V doesn't understand the kernel memory allocators.  So, below are
my attempts to make it do so.  These apply to UML, and describe the kernel
to V.

I don't guarantee that they are correct, but they should at least give you
an idea what needs to happen.

				Jeff

V doesn't see that PTRACE_FAULTINFO initializes the fault struct given to it:

diff -Naur um/arch/um/kernel/skas/process.c v/arch/um/kernel/skas/process.c
--- um/arch/um/kernel/skas/process.c	Tue Jan 14 21:09:16 2003
+++ v/arch/um/kernel/skas/process.c	Mon Dec 23 11:42:39 2002
@@ -25,6 +25,8 @@
 #include "proc_mm.h"
 #include "skas_ptrace.h"
 
+#include "memcheck.h"
+
 unsigned long exec_regs[FRAME_SIZE];
 unsigned long exec_fp_regs[HOST_FP_SIZE];
 unsigned long exec_fpx_regs[HOST_XFP_SIZE];
@@ -40,6 +42,7 @@
 		panic("handle_segv - PTRACE_FAULTINFO failed, errno = %d\n",
 		      errno);
 
+	VALGRIND_MAKE_READABLE(&fault, sizeof(fault));
 	segv(fault.addr, 0, FAULT_WRITE(fault.is_write), 1, NULL);
 }
 
This makes buffers writeable according to V when they are handed out by
the slab allocator, and no-access when they are freed:

diff -Naur um/mm/slab.c v/mm/slab.c
--- um/mm/slab.c	Fri Dec 20 18:42:53 2002
+++ v/mm/slab.c	Mon Dec 23 11:15:31 2002
@@ -76,6 +76,8 @@
 #include	<linux/seq_file.h>
 #include	<asm/uaccess.h>
 
+#include "memcheck.h"
+
 /*
  * DEBUG	- 1 for kmem_cache_create() to honour; SLAB_DEBUG_INITIAL,
  *		  SLAB_RED_ZONE & SLAB_POISON.
@@ -500,6 +502,11 @@
 	 * it is a named-page or buffer-page.  The members it tests are
 	 * of no interest here.....
 	 */
+
+	if(addr != NULL)
+	        VALGRIND_MAKE_WRITABLE(addr, 
+				       (1 << cachep->gfporder) * PAGE_SIZE);
+
 	return addr;
 }
 
@@ -1076,8 +1083,11 @@
 		 * the same cache which they are a constructor for.
 		 * Otherwise, deadlock. They must also be threaded.
 		 */
-		if (cachep->ctor)
+		if (cachep->ctor){
+		        VALGRIND_MAKE_WRITABLE(objp, cachep->objsize);
 			cachep->ctor(objp, cachep, ctor_flags);
+		        VALGRIND_MAKE_NOACCESS(objp, cachep->objsize);
+		}
 #if DEBUG
 		if (cachep->flags & SLAB_RED_ZONE)
 			objp -= BYTES_PER_WORD;
@@ -1528,7 +1538,11 @@
  */
 void * kmem_cache_alloc (kmem_cache_t *cachep, int flags)
 {
-	return __kmem_cache_alloc(cachep, flags);
+        void *ptr = __kmem_cache_alloc(cachep, flags);
+
+	if(ptr != NULL)
+	        VALGRIND_MAKE_READABLE(ptr, cachep->objsize);
+	return ptr;
 }
 
 /**
@@ -1557,10 +1571,16 @@
 	cache_sizes_t *csizep = cache_sizes;
 
 	for (; csizep->cs_size; csizep++) {
+   	        void *ptr;
 		if (size > csizep->cs_size)
 			continue;
-		return __kmem_cache_alloc(flags & GFP_DMA ?
-			 csizep->cs_dmacachep : csizep->cs_cachep, flags);
+		ptr = __kmem_cache_alloc(flags & GFP_DMA ?
+					 csizep->cs_dmacachep : 
+					 csizep->cs_cachep, flags);
+		if(ptr != NULL)
+		        VALGRIND_MAKE_WRITABLE(ptr, size);
+
+		return ptr;
 	}
 	return NULL;
 }

Ditto for vmalloc/vfree:

diff -Naur um/mm/vmalloc.c v/mm/vmalloc.c
--- um/mm/vmalloc.c	Mon Feb 25 12:50:45 2002
+++ v/mm/vmalloc.c	Mon Dec 23 11:30:26 2002
@@ -16,6 +16,8 @@
 #include <asm/uaccess.h>
 #include <asm/pgalloc.h>
 
+#include "memcheck.h"
+
 rwlock_t vmlist_lock = RW_LOCK_UNLOCKED;
 struct vm_struct * vmlist;
 
@@ -212,11 +214,14 @@
 		printk(KERN_ERR "Trying to vfree() bad address (%p)\n", addr);
 		return;
 	}
+
 	write_lock(&vmlist_lock);
 	for (p = &vmlist ; (tmp = *p) ; p = &tmp->next) {
 		if (tmp->addr == addr) {
 			*p = tmp->next;
 			vmfree_area_pages(VMALLOC_VMADDR(tmp->addr), tmp->size);
+			VALGRIND_MAKE_NOACCESS(VMALLOC_VMADDR(tmp->addr), 
+					      tmp->size);
 			write_unlock(&vmlist_lock);
 			kfree(tmp);
 			return;
@@ -244,6 +249,8 @@
 		vfree(addr);
 		return NULL;
 	}
+
+	VALGRIND_MAKE_WRITABLE(addr, size);
 	return addr;
 }
 



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