Messages in this thread | | | Date | Thu, 15 Feb 2024 11:51:39 -0500 | Subject | Re: [PATCH v8 2/2] lib: checksum: Use aligned accesses for ip_fast_csum and csum_ipv6_magic tests | From | John David Anglin <> |
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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. > } > > 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 Code entry points only need 4-byte alignment. > 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 Ditto. > 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
Dave
-- John David Anglin dave.anglin@bell.net
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