[PATCH v7 2/2] aarch64: add __ifunc_hwcap function to be used in ifunc resolvers
Adhemerval Zanella Netto
adhemerval.zanella@linaro.org
Thu Jun 5 13:18:32 GMT 2025
On 05/06/25 09:20, Yury Khrustalev wrote:
> Add a new helper function __ifunc_hwcap() as 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 returned when the requested element is not available
> or does not correspond to a valid AT_HWCAP{,2,...} value.
>
> Also add relevant tests.
Minor nit below.
LGTM, thanks.
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
> ---
> sysdeps/aarch64/Makefile | 7 ++-
> sysdeps/aarch64/sys/ifunc.h | 31 ++++++++++
> sysdeps/aarch64/tst-ifunc-arg-1.c | 12 ++++
> sysdeps/aarch64/tst-ifunc-arg-2.c | 11 ++++
> sysdeps/aarch64/tst-ifunc-arg-3.c | 97 +++++++++++++++++++++++++++++++
> sysdeps/aarch64/tst-ifunc-arg-4.c | 67 +++++++++++++++++++++
> 6 files changed, 224 insertions(+), 1 deletion(-)
> create mode 100644 sysdeps/aarch64/tst-ifunc-arg-3.c
> create mode 100644 sysdeps/aarch64/tst-ifunc-arg-4.c
>
> diff --git a/sysdeps/aarch64/Makefile b/sysdeps/aarch64/Makefile
> index 0fc6cf1693..021a35682b 100644
> --- a/sysdeps/aarch64/Makefile
> +++ b/sysdeps/aarch64/Makefile
> @@ -41,7 +41,12 @@ 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 \
> + tst-ifunc-arg-4 \
> + #tests-internal
>
> tests += tst-vpcs
> modules-names += tst-vpcs-mod
> diff --git a/sysdeps/aarch64/sys/ifunc.h b/sysdeps/aarch64/sys/ifunc.h
> index 42d173195f..a3322a9cfc 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)
>
> @@ -61,4 +63,33 @@ struct __ifunc_arg_t
>
> typedef struct __ifunc_arg_t __ifunc_arg_t;
>
> +/* Constants for IDs of HWCAP elements to be used with the
> + __ifunc_hwcap function below. */
> +enum
> +{
> + _IFUNC_ARG_AT_HWCAP = 1,
> + _IFUNC_ARG_AT_HWCAP2 = 2,
> + _IFUNC_ARG_AT_HWCAP3 = 3,
> + _IFUNC_ARG_AT_HWCAP4 = 4,
> +};
> +
> +/* 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, 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..49d8866e8b
> --- /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 (_IFUNC_ARG_AT_HWCAP, _IFUNC_ARG_HWCAP, arg), p1); \
> + TEST_COMPARE (__ifunc_hwcap (_IFUNC_ARG_AT_HWCAP2, _IFUNC_ARG_HWCAP, arg), p2); \
> + TEST_COMPARE (__ifunc_hwcap (_IFUNC_ARG_AT_HWCAP3, _IFUNC_ARG_HWCAP, arg), p3); \
> + TEST_COMPARE (__ifunc_hwcap (_IFUNC_ARG_AT_HWCAP4, _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 (_IFUNC_ARG_AT_HWCAP, p1, arg), p1); \
> + TEST_COMPARE (__ifunc_hwcap (_IFUNC_ARG_AT_HWCAP2, p1, arg), 0); \
> + TEST_COMPARE (__ifunc_hwcap (_IFUNC_ARG_AT_HWCAP3, p1, arg), 0); \
> + TEST_COMPARE (__ifunc_hwcap (_IFUNC_ARG_AT_HWCAP4, 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, /* Placeholder for size */
> + _IFUNC_ARG_AT_HWCAP, /* AT_HWCAP */
> + _IFUNC_ARG_AT_HWCAP2, /* AT_HWCAP2 */
> + _IFUNC_ARG_AT_HWCAP3, /* AT_HWCAP3 */
> + _IFUNC_ARG_AT_HWCAP4, /* 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>
> diff --git a/sysdeps/aarch64/tst-ifunc-arg-4.c b/sysdeps/aarch64/tst-ifunc-arg-4.c
> new file mode 100644
> index 0000000000..e7e2d8b5d4
> --- /dev/null
> +++ b/sysdeps/aarch64/tst-ifunc-arg-4.c
> @@ -0,0 +1,67 @@
> +/* Test for ifunc resolver that uses __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 <stdio.h>
> +#include <stdint.h>
> +#include <sys/auxv.h>
> +#include <sys/ifunc.h>
> +#include <support/check.h>
> +
> +static int
> +one (void)
> +{
> + return 1;
> +}
> +
> +static int
> +two (void)
> +{
> + return 2;
> +}
> +
> +/* Resolver function. */
> +static void *
> +resolver (uint64_t arg0, const uint64_t arg1[])
> +{
> + uint64_t hwcap2 = __ifunc_hwcap(_IFUNC_ARG_AT_HWCAP2, arg0, arg1);
Minor style nit: space after function name.
> + if (hwcap2 & HWCAP2_POE)
> + return (void *)one;
> + else
> + return (void *)two;
> +}
> +
> +/* An extern visible ifunc symbol. */
> +int fun (void) __attribute__((ifunc ("resolver")));
> +
> +static int
> +do_test (void)
> +{
> + if (getauxval (AT_HWCAP2) & HWCAP2_POE)
> + {
> + printf ("using 1st implementation\n");
> + TEST_VERIFY (fun () == 1);
> + }
> + else
> + {
> + printf ("using 2nd implementation\n");
> + TEST_VERIFY (fun () == 2);
> + }
> + return 0;
> +}
> +
> +#include <support/test-driver.c>
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