[PATCH v5 2/2] aarch64: helper function to access hwcap elements in ifunc resolver
enh
enh@google.com
Tue May 6 14:29:43 GMT 2025
On Tue, May 6, 2025 at 10:27 AM enh <enh@google.com> wrote:
>
> On Mon, Apr 28, 2025 at 7:32 AM Yury Khrustalev <yury.khrustalev@arm.com> wrote:
> >
> > Add a portable way to access HWCAP elements via the parameter(s)
> > passed to an ifunc resolver checking the _IFUNC_ARG_HWCAP bit in
> > the first parameter and size of the buffer in the second parameter.
> >
> > Note that 0 is return when the requested element is not available
> > or does not correspond to a valid AT_HWCAP{,2,...} value.
> > ---
> > sysdeps/aarch64/Makefile | 2 +-
> > sysdeps/aarch64/sys/ifunc.h | 21 +++++++
> > sysdeps/aarch64/tst-ifunc-arg-1.c | 12 ++++
> > sysdeps/aarch64/tst-ifunc-arg-2.c | 11 ++++
> > sysdeps/aarch64/tst-ifunc-arg-3.c | 97 +++++++++++++++++++++++++++++++
> > 5 files changed, 142 insertions(+), 1 deletion(-)
> > create mode 100644 sysdeps/aarch64/tst-ifunc-arg-3.c
> >
> > diff --git a/sysdeps/aarch64/Makefile b/sysdeps/aarch64/Makefile
> > index 4b7f8a5c07..c4d21336da 100644
> > --- a/sysdeps/aarch64/Makefile
> > +++ b/sysdeps/aarch64/Makefile
> > @@ -41,7 +41,7 @@ gen-as-const-headers += \
> > dl-link.sym \
> > rtld-global-offsets.sym
> >
> > -tests-internal += tst-ifunc-arg-1 tst-ifunc-arg-2
> > +tests-internal += tst-ifunc-arg-1 tst-ifunc-arg-2 tst-ifunc-arg-3
> >
> > ifeq (yes,$(aarch64-variant-pcs))
> > tests += tst-vpcs
> > diff --git a/sysdeps/aarch64/sys/ifunc.h b/sysdeps/aarch64/sys/ifunc.h
> > index fd4d49f00b..8d994f8418 100644
> > --- a/sysdeps/aarch64/sys/ifunc.h
> > +++ b/sysdeps/aarch64/sys/ifunc.h
> > @@ -19,6 +19,8 @@
> > #ifndef _SYS_IFUNC_H
> > #define _SYS_IFUNC_H
> >
> > +#include <sys/cdefs.h>
> > +
> > /* A second argument is passed to the ifunc resolver. */
> > #define _IFUNC_ARG_HWCAP (1ULL << 62)
> >
> > @@ -64,4 +66,23 @@ struct __ifunc_arg_t
> >
> > typedef struct __ifunc_arg_t __ifunc_arg_t;
> >
> > +/* A helper function to obtain HWCAP element by its ID from the
> > + parameters ARG0 and ARG1 passed to the ifunc resolver. Note that
> > + ID 1 corresponds to AT_HWCAP, ID 2 corresponds to AT_HWCAP2, etc.
> > + If there is no element available for the requested ID then 0 is
> > + returned. If ID doesn't much any supported AT_HWCAP{,2,...} value,
> > + then 0 is also returned. */
> > +static __inline unsigned long __attribute__ ((unused, always_inline))
> > +__ifunc_hwcap (unsigned long __id,
> > + unsigned long __arg0,
>
> is there any reason for this special case, since it's also available
> from the array? this just seems to make caller and callee slightly
> more complex for no significant advantage?
oh, it's to support the historical accident where glibc has versions
that _do_ pass arg0 but _don't_ pass arg1? (bionic went straight from
passing nothing to passing both arguments.)
> > const unsigned long *__arg1)
> > +{
> > + if (__glibc_likely (__arg0 & _IFUNC_ARG_HWCAP))
> > + {
> > + const unsigned long size = __arg1[0];
> > + const unsigned long offset = __id * sizeof (unsigned long);
> > + return offset < size && __id > 0 ? __arg1[__id] : 0;
> > + }
> > + return __id == 1 ? __arg0 : 0;
> > +}
> > +
> > #endif
> > diff --git a/sysdeps/aarch64/tst-ifunc-arg-1.c b/sysdeps/aarch64/tst-ifunc-arg-1.c
> > index 9cc3d40c48..292c5ae9e3 100644
> > --- a/sysdeps/aarch64/tst-ifunc-arg-1.c
> > +++ b/sysdeps/aarch64/tst-ifunc-arg-1.c
> > @@ -60,6 +60,18 @@ do_test (void)
> > TEST_COMPARE (saved_arg2._hwcap3, getauxval (AT_HWCAP3));
> > TEST_COMPARE (saved_arg2._hwcap4, getauxval (AT_HWCAP4));
> >
> > + const unsigned long *saved_arg2_ptr = (const unsigned long *)&saved_arg2;
> > +
> > + TEST_COMPARE (__ifunc_hwcap (1, saved_arg1, saved_arg2_ptr),
> > + getauxval (AT_HWCAP));
> > + TEST_COMPARE (__ifunc_hwcap (2, saved_arg1, saved_arg2_ptr),
> > + getauxval (AT_HWCAP2));
> > + TEST_COMPARE (__ifunc_hwcap (3, saved_arg1, saved_arg2_ptr),
> > + getauxval (AT_HWCAP3));
> > + TEST_COMPARE (__ifunc_hwcap (4, saved_arg1, saved_arg2_ptr),
> > + getauxval (AT_HWCAP4));
> > +
> > +
> > return 0;
> > }
> >
> > diff --git a/sysdeps/aarch64/tst-ifunc-arg-2.c b/sysdeps/aarch64/tst-ifunc-arg-2.c
> > index d9950f0e37..c05129a132 100644
> > --- a/sysdeps/aarch64/tst-ifunc-arg-2.c
> > +++ b/sysdeps/aarch64/tst-ifunc-arg-2.c
> > @@ -63,6 +63,17 @@ do_test (void)
> > TEST_COMPARE (saved_arg2._hwcap3, getauxval (AT_HWCAP3));
> > TEST_COMPARE (saved_arg2._hwcap4, getauxval (AT_HWCAP4));
> >
> > + const unsigned long *saved_arg2_ptr = (const unsigned long *)&saved_arg2;
> > +
> > + TEST_COMPARE (__ifunc_hwcap (1, saved_arg1, saved_arg2_ptr),
> > + getauxval (AT_HWCAP));
> > + TEST_COMPARE (__ifunc_hwcap (2, saved_arg1, saved_arg2_ptr),
> > + getauxval (AT_HWCAP2));
> > + TEST_COMPARE (__ifunc_hwcap (3, saved_arg1, saved_arg2_ptr),
> > + getauxval (AT_HWCAP3));
> > + TEST_COMPARE (__ifunc_hwcap (4, saved_arg1, saved_arg2_ptr),
> > + getauxval (AT_HWCAP4));
> > +
> > return 0;
> > }
> >
> > diff --git a/sysdeps/aarch64/tst-ifunc-arg-3.c b/sysdeps/aarch64/tst-ifunc-arg-3.c
> > new file mode 100644
> > index 0000000000..0f47a0a3b1
> > --- /dev/null
> > +++ b/sysdeps/aarch64/tst-ifunc-arg-3.c
> > @@ -0,0 +1,97 @@
> > +/* Tests for __ifunc_hwcap helper function.
> > + Copyright (C) 2025 Free Software Foundation, Inc.
> > + This file is part of the GNU C Library.
> > +
> > + The GNU C Library is free software; you can redistribute it and/or
> > + modify it under the terms of the GNU Lesser General Public
> > + License as published by the Free Software Foundation; either
> > + version 2.1 of the License, or (at your option) any later version.
> > +
> > + The GNU C Library is distributed in the hope that it will be useful,
> > + but WITHOUT ANY WARRANTY; without even the implied warranty of
> > + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
> > + Lesser General Public License for more details.
> > +
> > + You should have received a copy of the GNU Lesser General Public
> > + License along with the GNU C Library; if not, see
> > + <https://www.gnu.org/licenses/>. */
> > +
> > +#include <stdint.h>
> > +#include <sys/ifunc.h>
> > +#include <support/check.h>
> > +
> > +#define CHECK_VALUES_WITH_ARG(p1, p2, p3, p4) \
> > + ({ \
> > + TEST_COMPARE (__ifunc_hwcap (0, _IFUNC_ARG_HWCAP, arg), 0); \
> > + TEST_COMPARE (__ifunc_hwcap (1, _IFUNC_ARG_HWCAP, arg), p1); \
> > + TEST_COMPARE (__ifunc_hwcap (2, _IFUNC_ARG_HWCAP, arg), p2); \
> > + TEST_COMPARE (__ifunc_hwcap (3, _IFUNC_ARG_HWCAP, arg), p3); \
> > + TEST_COMPARE (__ifunc_hwcap (4, _IFUNC_ARG_HWCAP, arg), p4); \
> > + TEST_COMPARE (__ifunc_hwcap (5, _IFUNC_ARG_HWCAP, arg), 0); \
> > + })
> > +
> > +#define CHECK_VALUES_WITHOUT_ARG(p1) \
> > + ({ \
> > + TEST_COMPARE (__ifunc_hwcap (0, p1, arg), 0); \
> > + TEST_COMPARE (__ifunc_hwcap (1, p1, arg), p1); \
> > + TEST_COMPARE (__ifunc_hwcap (2, p1, arg), 0); \
> > + TEST_COMPARE (__ifunc_hwcap (3, p1, arg), 0); \
> > + TEST_COMPARE (__ifunc_hwcap (4, p1, arg), 0); \
> > + TEST_COMPARE (__ifunc_hwcap (5, p1, arg), 0); \
> > + })
> > +
> > +static void
> > +test_one (const unsigned long *arg)
> > +{
> > + uint64_t size = arg[0] / sizeof (uint64_t);
> > +
> > + switch (size)
> > + {
> > + case 1:
> > + CHECK_VALUES_WITH_ARG (0, 0, 0, 0);
> > + CHECK_VALUES_WITHOUT_ARG (0);
> > + break;
> > + case 2:
> > + CHECK_VALUES_WITH_ARG (1, 0, 0, 0);
> > + CHECK_VALUES_WITHOUT_ARG (1);
> > + break;
> > + case 3:
> > + CHECK_VALUES_WITH_ARG (1, 2, 0, 0);
> > + CHECK_VALUES_WITHOUT_ARG (1);
> > + break;
> > + case 4:
> > + CHECK_VALUES_WITH_ARG (1, 2, 3, 0);
> > + CHECK_VALUES_WITHOUT_ARG (1);
> > + break;
> > + case 5:
> > + CHECK_VALUES_WITH_ARG (1, 2, 3, 4);
> > + CHECK_VALUES_WITHOUT_ARG (1);
> > + break;
> > + default:
> > + TEST_VERIFY (0); // unexpected size
> > + break;
> > + }
> > +}
> > +
> > +static int
> > +do_test (void)
> > +{
> > + uint64_t arg[_IFUNC_HWCAP_MAX + 1] = {
> > + 0, /* Size */
> > + 1, /* AT_HWCAP */
> > + 2, /* AT_HWCAP2 */
> > + 3, /* AT_HWCAP3 */
> > + 4, /* AT_HWCAP4 */
> > + };
> > +
> > + for (int k = 0; k <= _IFUNC_HWCAP_MAX; k++)
> > + {
> > + /* Update size */
> > + arg[0] = (k + 1) * sizeof (uint64_t);
> > + test_one (arg);
> > + }
> > +
> > + return 0;
> > +}
> > +
> > +#include <support/test-driver.c>
> > --
> > 2.39.5
> >
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