Messages in this thread Patch in this message | | | Date | Thu, 15 Feb 2024 07:44:36 -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 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; }
Disassembled:
c38: 50 3c 00 00 ldd 0(r1),ret0 c3c: 08 1b 02 44 copy dp,r4 c40: 0f 80 10 da ldd 0(ret0),r26 <-- c44: 37 dd 3f a1 ldo -30(sp),ret1 c48: 51 02 00 20 ldd 10(r8),rp c4c: e8 40 f0 00 bve,l (rp),rp c50: 51 1b 00 30 ldd 18(r8),dp
Hmm, interesting. See below for a possible fix. Should I submit a patch ?
Thanks, Guenter
--- diff --git a/arch/parisc/kernel/entry.S b/arch/parisc/kernel/entry.S index ab23e61a6f01..1d2aab619466 100644 --- a/arch/parisc/kernel/entry.S +++ b/arch/parisc/kernel/entry.S @@ -772,6 +772,7 @@ ENTRY_CFI(_switch_to) bv %r0(%r2) mtctl %r25,%cr30
+ .align 8 ENTRY(_switch_to_ret) mtctl %r0, %cr0 /* Needed for single stepping */ callee_rest @@ -1702,6 +1703,7 @@ ENTRY_CFI(sys_rt_sigreturn_wrapper) LDREG PT_GR28(%r1),%r28 /* reload original r28 for syscall_exit */ ENDPROC_CFI(sys_rt_sigreturn_wrapper)
+ .align 8 ENTRY(syscall_exit) /* NOTE: Not all syscalls exit this way. rt_sigreturn will exit * via syscall_exit_rfi if the signal was received while the process
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