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Fixing /proc/kcore

Linux-ia64 Luck, Tony 1 participant 1 message Oct 25, 2002

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Luck, Tony

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/proc/kcore is what you need, but it is broken on ia64 (and has been since the dawn of time for access to region 5) because it assumes that all kernel virtual addresses are above PAGE_OFFSET. This isn't true on ia64, VMALLOC_START is smaller than PAGE_OFFSET.

Attached is a patch (applies to 2.4.19 and to 2.5.39) that fixes the assumption. After applying you'll be able to use:

	# gdb vmlinux /proc/kcore

and happily ask gdb to examine addresses in region 5.

-Tony Luck

-----Original Message-----
From: Mario Smarduch [mailto:[email protected]]
Sent: Friday, October 25, 2002 7:36 AM
To: IA64 Linux Mail Group
Subject: [Linux-ia64] Debugger/Analysis tool for IA64 Kernel Reg 5

Hi,
I'm wondering if there is a tool available (gdb or some crash
analysis
tool) that can be used to disassemble/dump region 5 pages? We recently have ported LiS and OpenSS7 stacks to IA-64 and it was painful without being able to debug the Reg 5 memory, but we'll still be doing more work.
We currently just have a crude tool that gets the reg 7 address from a reg 5 address and then we use gdb, this is pretty cumbersome.....

- Mario.

fs/proc/kcore.c renamed from ../REF/linux-2.5.39-ia64-020928/fs/proc/kcore.c +14 -8
diff -ru ../../REF/linux-2.5.39-ia64-020928/fs/proc/kcore.c aegl-kcore/fs/proc/kcore.c
@@ -99,6 +99,12 @@
 }
 #else /* CONFIG_KCORE_AOUT */
 
+#if VMALLOC_START < PAGE_OFFSET
+#define	KCORE_BASE	VMALLOC_START
+#else
+#define	KCORE_BASE	PAGE_OFFSET
+#endif
+
 #define roundup(x, y)  ((((x)+((y)-1))/(y))*(y))
 
 /* An ELF note in memory */

@@ -118,7 +124,7 @@
 	struct vm_struct *m;
 
 	*num_vma = 0;
-	size = ((size_t)high_memory - PAGE_OFFSET + PAGE_SIZE);
+	size = ((size_t)high_memory - KCORE_BASE + PAGE_SIZE);
 	if (!vmlist) {
 		*elf_buflen = PAGE_SIZE;
 		return (size);

@@ -126,15 +132,15 @@
 
 	for (m=vmlist; m; m=m->next) {
 		try = (size_t)m->addr + m->size;
-		if (try > size)
-			size = try;
+		if (try > KCORE_BASE + size)
+			size = try - KCORE_BASE;
 		*num_vma = *num_vma + 1;
 	}
 	*elf_buflen =	sizeof(struct elfhdr) + 
 			(*num_vma + 2)*sizeof(struct elf_phdr) + 
 			3 * sizeof(struct memelfnote);
 	*elf_buflen = PAGE_ALIGN(*elf_buflen);
-	return (size - PAGE_OFFSET + *elf_buflen);
+	return size + *elf_buflen;
 }
 
 

@@ -237,7 +243,7 @@
 	offset += sizeof(struct elf_phdr);
 	phdr->p_type	= PT_LOAD;
 	phdr->p_flags	= PF_R|PF_W|PF_X;
-	phdr->p_offset	= dataoff;
+	phdr->p_offset	= PAGE_OFFSET - KCORE_BASE + dataoff;
 	phdr->p_vaddr	= PAGE_OFFSET;
 	phdr->p_paddr	= __pa(PAGE_OFFSET);
 	phdr->p_filesz	= phdr->p_memsz = ((unsigned long)high_memory - PAGE_OFFSET);

@@ -254,7 +260,7 @@
 
 		phdr->p_type	= PT_LOAD;
 		phdr->p_flags	= PF_R|PF_W|PF_X;
-		phdr->p_offset	= (size_t)m->addr - PAGE_OFFSET + dataoff;
+		phdr->p_offset	= (size_t)m->addr - KCORE_BASE + dataoff;
 		phdr->p_vaddr	= (size_t)m->addr;
 		phdr->p_paddr	= __pa(m->addr);
 		phdr->p_filesz	= phdr->p_memsz	= m->size;

@@ -385,9 +391,9 @@
 	/*
 	 * Fill the remainder of the buffer from kernel VM space.
 	 * We said in the ELF header that the data which starts
-	 * at 'elf_buflen' is virtual address PAGE_OFFSET. --rmk
+	 * at 'elf_buflen' is virtual address KCORE_BASE. --rmk
 	 */
-	start = PAGE_OFFSET + (*fpos - elf_buflen);
+	start = KCORE_BASE + (*fpos - elf_buflen);
 	if ((tsz = (PAGE_SIZE - (start & ~PAGE_MASK))) > buflen)
 		tsz = buflen;