[RFC PATCH] riscv: Add support for STT_GNU_IFUNC symbols

[Vincent Chen]

This patch adds the support for STT_GNU_IFUNC symbols to riscv ports. The
Binutils' IFUNC patches are under reviewing and can be found in 
https://sourceware.org/pipermail/binutils/2020-July/112186.html.

Any suggestions and feedback are welcome. 
---
 sysdeps/riscv/dl-irel.h    | 53 ++++++++++++++++++++++++++++++++++++++++++++++
 sysdeps/riscv/dl-machine.h | 22 ++++++++++++++++++-
 2 files changed, 74 insertions(+), 1 deletion(-)
 create mode 100644 sysdeps/riscv/dl-irel.h

diff --git a/sysdeps/riscv/dl-irel.h b/sysdeps/riscv/dl-irel.h
new file mode 100644
index 0000000..9dd8de9
--- /dev/null
+++ b/sysdeps/riscv/dl-irel.h
@@ -0,0 +1,53 @@
+/* Machine-dependent ELF indirect relocation inline functions.
+   RISC-V version.
+   Copyright (C) 2012-2020 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/>.  */
+
+#ifndef _DL_IREL_H
+#define _DL_IREL_H
+
+#include <stdio.h>
+#include <unistd.h>
+#include <ldsodefs.h>
+#include <sysdep.h>
+
+#define ELF_MACHINE_IRELA	1
+
+static inline ElfW(Addr)
+__attribute ((always_inline))
+elf_ifunc_invoke (ElfW(Addr) addr)
+{
+  return ((ElfW(Addr) (*) (uint64_t)) (addr)) (GLRO(dl_hwcap));
+}
+
+static inline void
+__attribute ((always_inline))
+elf_irela (const ElfW(Rela) *reloc)
+{
+  ElfW(Addr) *const reloc_addr = (void *) reloc->r_offset;
+  const unsigned long int r_type = ELFW(R_TYPE) (reloc->r_info);
+
+  if (__glibc_likely (r_type == R_RISCV_IRELATIVE))
+    {
+      ElfW(Addr) value = elf_ifunc_invoke (reloc->r_addend);
+      *reloc_addr = value;
+    }
+  else
+    __libc_fatal ("Unexpected reloc type in static binary.\n");
+}
+
+#endif
diff --git a/sysdeps/riscv/dl-machine.h b/sysdeps/riscv/dl-machine.h
index 03db94a..728e6d3 100644
--- a/sysdeps/riscv/dl-machine.h
+++ b/sysdeps/riscv/dl-machine.h
@@ -25,6 +25,7 @@
 #include <elf/elf.h>
 #include <sys/asm.h>
 #include <dl-tls.h>
+#include <dl-irel.h>
 
 #ifndef _RTLD_PROLOGUE
 # define _RTLD_PROLOGUE(entry)						\
@@ -174,6 +175,13 @@ elf_machine_rela (struct link_map *map, const ElfW(Rela) *reloc,
   if (sym_map != NULL)
     value = SYMBOL_ADDRESS (sym_map, sym, true) + reloc->r_addend;
 
+  if (sym != NULL
+      && __glibc_unlikely (ELFW(ST_TYPE) (sym->st_info) == STT_GNU_IFUNC)
+      && __glibc_likely (sym->st_shndx != SHN_UNDEF)
+      && __glibc_likely (!skip_ifunc))
+    value = elf_ifunc_invoke (value);
+
+
   switch (r_type)
     {
 #ifndef RTLD_BOOTSTRAP
@@ -248,7 +256,12 @@ elf_machine_rela (struct link_map *map, const ElfW(Rela) *reloc,
       break;
     }
 #endif
-
+    case R_RISCV_IRELATIVE:
+      value = map->l_addr + reloc->r_addend;
+      if (__glibc_likely (!skip_ifunc))
+        value = elf_ifunc_invoke (value);
+      *addr_field = value;
+      break;
     case R_RISCV_JUMP_SLOT:
     case __WORDSIZE == 64 ? R_RISCV_64 : R_RISCV_32:
       *addr_field = value;
@@ -290,6 +303,13 @@ elf_machine_lazy_rel (struct link_map *map, ElfW(Addr) l_addr,
       else
 	*reloc_addr = map->l_mach.plt;
     }
+  else if (__glibc_unlikely (r_type == R_RISCV_IRELATIVE))
+    {
+      ElfW(Addr) value = map->l_addr + reloc->r_addend;
+      if (__glibc_likely (!skip_ifunc))
+        value = elf_ifunc_invoke (value);
+      *reloc_addr = value;
+    }
   else
     _dl_reloc_bad_type (map, r_type, 1);
 }
-- 
2.7.4