Messages in this thread Patch in this message | | | Date | Thu, 15 Feb 2024 10:42:29 -0800 | Subject | Re: [PATCH v8 2/2] lib: checksum: Use aligned accesses for ip_fast_csum and csum_ipv6_magic tests | From | Guenter Roeck <> |
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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];
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