[v8,4/6] riscv: Enable multi-arg ifunc resolvers

Message ID 20230901235224.3304592-5-evan@rivosinc.com
State Superseded
Series RISC-V: ifunced memcpy using new kernel hwprobe interface |


Context Check Description
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Commit Message

Evan Green Sept. 1, 2023, 11:52 p.m. UTC
  RISC-V is apparently the first architecture to pass more than one
argument to ifunc resolvers. The helper macros in libc-symbols.h,
__ifunc_resolver(), __ifunc(), and __ifunc_hidden(), are incompatible
with this. These macros have an "arg" (non-final) parameter that
represents the parameter signature of the ifunc resolver. The result is
an inability to pass the required comma through in a single preprocessor

Rearrange the __ifunc_resolver() macro to be variadic, and pass the
types as those variable parameters. Move the guts of __ifunc() and
__ifunc_hidden() into new macros, __ifunc_args(), and
__ifunc_args_hidden(), that pass the variable arguments down through to
__ifunc_resolver(). Then redefine __ifunc() and __ifunc_hidden(), which
are used in a bunch of places, to simply shuffle the arguments down into
__ifunc_args[_hidden]. Finally, define a riscv-ifunc.h header, which
provides convenience macros to those looking to write ifunc selectors
that use both arguments.

Signed-off-by: Evan Green <evan@rivosinc.com>


(no changes since v6)

Changes in v6:
 - Introduced riscv-ifunc.h for multi-arg ifunc selectors.

Note: I opted to create another layer of macros (__ifunc_args()) rather
than doing the treewide change to rearrange the signature of __ifunc()
and __ifunc_hidden(). If folks like the overall approach but would
prefer the treewide change, I can do that too.

 include/libc-symbols.h      | 28 +++++++++++++++++-----------
 sysdeps/riscv/riscv-ifunc.h | 27 +++++++++++++++++++++++++++
 2 files changed, 44 insertions(+), 11 deletions(-)
 create mode 100644 sysdeps/riscv/riscv-ifunc.h


diff --git a/include/libc-symbols.h b/include/libc-symbols.h
index 5794614488..36b92039c5 100644
--- a/include/libc-symbols.h
+++ b/include/libc-symbols.h
@@ -665,9 +665,9 @@  for linking")
 /* Helper / base  macros for indirect function symbols.  */
-#define __ifunc_resolver(type_name, name, expr, arg, init, classifier)	\
+#define __ifunc_resolver(type_name, name, expr, init, classifier, ...)	\
   classifier inhibit_stack_protector					\
-  __typeof (type_name) *name##_ifunc (arg)				\
+  __typeof (type_name) *name##_ifunc (__VA_ARGS__)			\
   {									\
     init ();								\
     __typeof (type_name) *res = expr;					\
@@ -675,13 +675,13 @@  for linking")
-# define __ifunc(type_name, name, expr, arg, init)			\
+# define __ifunc_args(type_name, name, expr, init, ...)			\
   extern __typeof (type_name) name __attribute__			\
 			      ((ifunc (#name "_ifunc")));		\
-  __ifunc_resolver (type_name, name, expr, arg, init, static)
+  __ifunc_resolver (type_name, name, expr, init, static, __VA_ARGS__)
-# define __ifunc_hidden(type_name, name, expr, arg, init)	\
-  __ifunc (type_name, name, expr, arg, init)
+# define __ifunc_args_hidden(type_name, name, expr, init, ...)		\
+  __ifunc (type_name, name, expr, init, __VA_ARGS__)
 /* Gcc does not support __attribute__ ((ifunc (...))).  Use the old behaviour
    as fallback.  But keep in mind that the debug information for the ifunc
@@ -692,18 +692,24 @@  for linking")
    different signatures.  (Gcc support is disabled at least on a ppc64le
    Ubuntu 14.04 system.)  */
-# define __ifunc(type_name, name, expr, arg, init)			\
+# define __ifunc_args(type_name, name, expr, init, ...)			\
   extern __typeof (type_name) name;					\
-  __typeof (type_name) *name##_ifunc (arg) __asm__ (#name);		\
-  __ifunc_resolver (type_name, name, expr, arg, init,)			\
+  __typeof (type_name) *name##_ifunc (__VA_ARGS__) __asm__ (#name);	\
+  __ifunc_resolver (type_name, name, expr, init, , __VA_ARGS__)		\
  __asm__ (".type " #name ", %gnu_indirect_function");
-# define __ifunc_hidden(type_name, name, expr, arg, init)		\
+# define __ifunc_args_hidden(type_name, name, expr, init, ...)		\
   extern __typeof (type_name) __libc_##name;				\
-  __ifunc (type_name, __libc_##name, expr, arg, init)			\
+  __ifunc (type_name, __libc_##name, expr, __VA_INIT__, init)		\
   strong_alias (__libc_##name, name);
 #endif /* !HAVE_GCC_IFUNC  */
+#define __ifunc(type_name, name, expr, arg, init)			\
+  __ifunc_args (type_name, name, expr, init, arg)
+#define __ifunc_hidden(type_name, name, expr, arg, init)		\
+  __ifunc_args_hidden (type_name, expr, init, arg)
 /* The following macros are used for indirect function symbols in libc.so.
    First of all, you need to have the function prototyped somewhere,
    say in foo.h:
diff --git a/sysdeps/riscv/riscv-ifunc.h b/sysdeps/riscv/riscv-ifunc.h
new file mode 100644
index 0000000000..7bff591d1e
--- /dev/null
+++ b/sysdeps/riscv/riscv-ifunc.h
@@ -0,0 +1,27 @@ 
+/* Common definition for ifunc resolvers.  Linux/RISC-V version.
+   This file is part of the GNU C Library.
+   Copyright (C) 2023 Free Software Foundation, Inc.
+   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
+   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 <sysdep.h>
+#include <ifunc-init.h>
+#include <sys/hwprobe.h>
+#define INIT_ARCH()
+#define riscv_libc_ifunc(name, expr)				\
+  __ifunc_args (name, name, expr(hwcap, hwprobe), INIT_ARCH,	\
+                uint64_t hwcap, __riscv_hwprobe_t hwprobe)