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Subject[PATCH] Kdump: Align 64-bit ELF crash notes correctly (x86_64, powerpc)
Kdump: Align 64-bit ELF crash notes correctly (x86_64, powerpc)

The current ELF code aligns data to 32-bit addresses, regardless if ELFCLASS32
or ELFCLASS64 is used. This works well for the 32-bit case, but for 64-bit
notes we should (of course) align to 64-bit addresses. At least if we intend
to follow the "ELF-64 Object File Format, Version 1.5 Draft 2, May 27, 1998".

Unfortunately this change affects 3 pieces of code:
- The regular Linux kernel: See x86_64 and powerpc changes below.
- The "crash" kernel: Needs to align properly when merging notes, see below.
- The utilities that read the vmcore files: Crash, GDB and so on.

I am sure that this change will cause all sorts of trouble if someone is using
a certain combination of kernels and tools, but I believe the best long-term
solution is simply to fix this properly as soon as possible and live with the
fact that 64-bit vmcore files may have been broken up until now.

Signed-off-by: Magnus Damm <magnus@valinux.co.jp>
---

Compiles on x86_64, powerpc code only dry-coded.
Applies on top of 2.6.19-rc3.

arch/powerpc/kernel/crash.c | 18 +++++++++++-------
arch/x86_64/kernel/crash.c | 14 +++++++-------
fs/proc/vmcore.c | 4 ++--
3 files changed, 20 insertions(+), 16 deletions(-)

--- 0001/arch/powerpc/kernel/crash.c
+++ work/arch/powerpc/kernel/crash.c 2006-10-26 17:09:33.000000000 +0900
@@ -41,12 +41,16 @@
#define DBG(fmt...)
#endif

+#define ELF_ALIGN(x) ((x + (sizeof(elf_addr_t) - 1)) \
+ & ~(sizeof(elf_addr_t) - 1))
+
/* This keeps a track of which one is crashing cpu. */
int crashing_cpu = -1;
static cpumask_t cpus_in_crash = CPU_MASK_NONE;
cpumask_t cpus_in_sr = CPU_MASK_NONE;

-static u32 *append_elf_note(u32 *buf, char *name, unsigned type, void *data,
+static unsigned char *
+append_elf_note(unsigned char *buf, char *name, unsigned type, void *data,
size_t data_len)
{
struct elf_note note;
@@ -55,16 +59,16 @@ static u32 *append_elf_note(u32 *buf, ch
note.n_descsz = data_len;
note.n_type = type;
memcpy(buf, &note, sizeof(note));
- buf += (sizeof(note) +3)/4;
+ buf += ELF_ALIGN(sizeof(note));
memcpy(buf, name, note.n_namesz);
- buf += (note.n_namesz + 3)/4;
+ buf += ELF_ALIGN(note.n_namesz);
memcpy(buf, data, note.n_descsz);
- buf += (note.n_descsz + 3)/4;
+ buf += ELF_ALIGN(note.n_descsz);

return buf;
}

-static void final_note(u32 *buf)
+static void final_note(unsigned char *buf)
{
struct elf_note note;

@@ -77,7 +81,7 @@ static void final_note(u32 *buf)
static void crash_save_this_cpu(struct pt_regs *regs, int cpu)
{
struct elf_prstatus prstatus;
- u32 *buf;
+ unsigned char *buf;

if ((cpu < 0) || (cpu >= NR_CPUS))
return;
@@ -89,7 +93,7 @@ static void crash_save_this_cpu(struct p
* squirrelled away. ELF notes happen to provide
* all of that that no need to invent something new.
*/
- buf = (u32*)per_cpu_ptr(crash_notes, cpu);
+ buf = (unsigned char *)per_cpu_ptr(crash_notes, cpu);
if (!buf)
return;

--- 0002/arch/x86_64/kernel/crash.c
+++ work/arch/x86_64/kernel/crash.c 2006-10-26 16:58:18.000000000 +0900
@@ -28,7 +28,7 @@
/* This keeps a track of which one is crashing cpu. */
static int crashing_cpu;

-static u32 *append_elf_note(u32 *buf, char *name, unsigned type,
+static u64 *append_elf_note(u64 *buf, char *name, unsigned type,
void *data, size_t data_len)
{
struct elf_note note;
@@ -37,16 +37,16 @@ static u32 *append_elf_note(u32 *buf, ch
note.n_descsz = data_len;
note.n_type = type;
memcpy(buf, &note, sizeof(note));
- buf += (sizeof(note) +3)/4;
+ buf += (sizeof(note) + 7) / 8;
memcpy(buf, name, note.n_namesz);
- buf += (note.n_namesz + 3)/4;
+ buf += (note.n_namesz + 7) / 8;
memcpy(buf, data, note.n_descsz);
- buf += (note.n_descsz + 3)/4;
+ buf += (note.n_descsz + 7) / 8;

return buf;
}

-static void final_note(u32 *buf)
+static void final_note(u64 *buf)
{
struct elf_note note;

@@ -59,7 +59,7 @@ static void final_note(u32 *buf)
static void crash_save_this_cpu(struct pt_regs *regs, int cpu)
{
struct elf_prstatus prstatus;
- u32 *buf;
+ u64 *buf;

if ((cpu < 0) || (cpu >= NR_CPUS))
return;
@@ -72,7 +72,7 @@ static void crash_save_this_cpu(struct p
* all of that, no need to invent something new.
*/

- buf = (u32*)per_cpu_ptr(crash_notes, cpu);
+ buf = (u64*)per_cpu_ptr(crash_notes, cpu);

if (!buf)
return;
--- 0001/fs/proc/vmcore.c
+++ work/fs/proc/vmcore.c 2006-10-26 17:31:36.000000000 +0900
@@ -256,8 +256,8 @@ static int __init merge_note_headers_elf
if (nhdr_ptr->n_namesz == 0)
break;
sz = sizeof(Elf64_Nhdr) +
- ((nhdr_ptr->n_namesz + 3) & ~3) +
- ((nhdr_ptr->n_descsz + 3) & ~3);
+ ((nhdr_ptr->n_namesz + 7) & ~7) +
+ ((nhdr_ptr->n_descsz + 7) & ~7);
real_sz += sz;
nhdr_ptr = (Elf64_Nhdr*)((char*)nhdr_ptr + sz);
}
-
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