On 2/15/24 09:25, John David Anglin wrote:
On 2024-02-15 12:06 p.m., Guenter Roeck wrote:
On 2/15/24 08:51, John David Anglin wrote:
On 2024-02-15 10:44 a.m., Guenter Roeck wrote:
On 2/15/24 02:27, David Laight wrote:
...
It would be worthwhile tracking this down since there are
lots of unaligned data accesses (8-byte accesses on 4-byte aligned addresses)
when running the kernel in 64-bit mode.
Hmmm....
For performance reasons you really don't want any of them.
The misaligned 64bit fields need an __attribute((aligned(4)) marker.
If the checksum code can do them it really needs to detect
and handle the misalignment.
The misaligned trap handler probably ought to contain a
warn_on_once() to dump stack on the first such error.
They can then be fixed one at a time.
Unaligned LDD at unwind_once+0x4a8/0x5e0
Decoded:
Unaligned LDD at unwind_once (arch/parisc/kernel/unwind.c:212 arch/parisc/kernel/unwind.c:243 arch/parisc/kernel/unwind.c:371 arch/parisc/kernel/unwind.c:445)
Source:
static bool pc_is_kernel_fn(unsigned long pc, void *fn)
{
return (unsigned long)dereference_kernel_function_descriptor(fn) == pc;
This looks wrong to me. Function descriptors should always be 8-byte aligned. I think this
routine should return false if fn isn't 8-byte aligned.
Below you state "Code entry points only need 4-byte alignment."
I think that contradicts each other. Also, the calling code is,
for example,
pc_is_kernel_fn(pc, syscall_exit)
I fail to see how this can be consolidated if it is ok
that syscall_exit is 4-byte aligned but, at the same time,
must be 8-byte aligned to be considered to be a kernel function.
In the above call, syscall_exit is treated as a function pointer. It points to an 8-byte aligned
function descriptor. The descriptor holds the actual address of the function. It only needs
4-byte alignment.
Descriptors need 8-byte alignment for efficiency on 64-bit parisc. The pc and gp are accessed
using ldd instructions.
How about the patch below ?
Guenter
---
diff --git a/arch/parisc/kernel/unwind.c b/arch/parisc/kernel/unwind.c
index 27ae40a443b8..c2b9e23cbc0a 100644
--- a/arch/parisc/kernel/unwind.c
+++ b/arch/parisc/kernel/unwind.c
@@ -214,24 +214,14 @@ static bool pc_is_kernel_fn(unsigned long pc, void *fn)
static int unwind_special(struct unwind_frame_info *info, unsigned long pc, int frame_size)
{
- /*
- * We have to use void * instead of a function pointer, because
- * function pointers aren't a pointer to the function on 64-bit.
- * Make them const so the compiler knows they live in .text
- * Note: We could use dereference_kernel_function_descriptor()
- * instead but we want to keep it simple here.
- */
- extern void * const ret_from_kernel_thread;
- extern void * const syscall_exit;
- extern void * const intr_return;
- extern void * const _switch_to_ret;
+ void (*ret_from_kernel_thread)(void);
+ void (*syscall_exit)(void);
+ void (*intr_return)(void);
+ void (*_switch_to_ret)(void);
#ifdef CONFIG_IRQSTACKS
- extern void * const _call_on_stack;
+ void (*_call_on_stack)(void);
#endif /* CONFIG_IRQSTACKS */
- void *ptr;
-
- ptr = dereference_kernel_function_descriptor(&handle_interruption);
- if (pc_is_kernel_fn(pc, ptr)) {
+ if (pc_is_kernel_fn(pc, handle_interruption)) {
struct pt_regs *regs = (struct pt_regs *)(info->sp - frame_size - PT_SZ_ALGN);
dbg("Unwinding through handle_interruption()\n");
info->prev_sp = regs->gr[30];
