Messages in this thread Patch in this message | | | From | Nick Desaulniers <> | Date | Wed, 28 Sep 2022 13:49:32 -0700 | Subject | Re: [PATCH v3] x86, mem: move memmove to out of line assembler |
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On Wed, Sep 28, 2022 at 12:06 PM Nick Desaulniers <ndesaulniers@google.com> wrote: > > On Wed, Sep 28, 2022 at 12:24 AM Rasmus Villemoes > <linux@rasmusvillemoes.dk> wrote: > > > > On 27/09/2022 23.02, Nick Desaulniers wrote: > > > > > + /* > > > + * Handle data forward by movs. > > > + */ > > > +.p2align 4 > > > +.Lforward_movs: > > > + movl -4(src, n), tmp0 > > > + leal -4(dest, n), tmp1 > > > + shrl $2, n > > > + rep movsl > > > + movl tmp0, (tmp1) > > > + jmp .Ldone > > > > So in the original code, %1 was forced to be %esi and %2 was forced to > > be %edi and they were initialized by src and dest. But here I fail to > > see how those registers have been properly set up before the rep movs; > > your names for those are tmp0 and tmp2. You have just loaded the last > > word of the source to %edi, and AFAICT %esi aka tmp2 is entirely > > uninitialized at this point (the only use is in L16_byteswap). > > > > I must be missing something. Please enlighten me. > > No, you're right. It looks like rep movsl needs src in %esi and dest > needs to be in %edi, so I can't reuse the input registers from > -mregparm=3; a pair of movs is required. A v4 is required. > > Probably should write a test for memcpy where n > magic constant 680.
This unit test hangs with v3 (and passes with my local v4 which I haven't sent out yet): ``` index 62f8ffcbbaa3..c2e852762846 100644 --- a/lib/memcpy_kunit.c +++ b/lib/memcpy_kunit.c @@ -107,6 +107,8 @@ static void memcpy_test(struct kunit *test) #undef TEST_OP }
+static unsigned char larger_array [2048]; + static void memmove_test(struct kunit *test) { #define TEST_OP "memmove" @@ -181,6 +183,20 @@ static void memmove_test(struct kunit *test) ptr = &overlap.data[2]; memmove(ptr, overlap.data, 5); compare("overlapping write", overlap, overlap_expected); + + /* Verify larger overlapping moves. */ + larger_array[256] = 0xaa; + memmove(larger_array, larger_array + 256, 1024); + KUNIT_ASSERT_EQ(test, larger_array[0], 0xaa); + KUNIT_ASSERT_EQ(test, larger_array[256], 0x00); + KUNIT_ASSERT_NULL(test, + memchr(larger_array + 1, 0xaa, ARRAY_SIZE(larger_array) - 1)); ``` I'll include the tests in my v4, including another for overlapping memmove forwards. -- Thanks, ~Nick Desaulniers
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