[PATCH v6 2/2] aarch64: add __ifunc_hwcap function to be used in ifunc resolvers
Yury Khrustalev
yury.khrustalev@arm.com
Tue May 13 14:13:48 GMT 2025
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 return when the requested element is not available
or does not correspond to a valid AT_HWCAP{,2,...} value.
Also add relevant tests.
---
sysdeps/aarch64/Makefile | 7 ++-
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 +++++++++++++++++++++++++++++++
sysdeps/aarch64/tst-ifunc-arg-4.c | 67 +++++++++++++++++++++
6 files changed, 214 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 4b7f8a5c07..b9929dc8e9 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
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, 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>
diff --git a/sysdeps/aarch64/tst-ifunc-arg-4.c b/sysdeps/aarch64/tst-ifunc-arg-4.c
new file mode 100644
index 0000000000..067fd7b5fe
--- /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(2, arg0, arg1);
+ 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>
--
2.39.5
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