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Hi,
This is a follow up on IFUNC support for MIPS. Previous patch discussion on this list was:
https://sourceware.org/ml/libc-ports/2013-08/msg00007.html
This patch is intended to work with the corresponding binutils patch, on-going review at:
https://sourceware.org/ml/binutils/2015-07/msg00213.html
Detailed description is in the attached text file. Please comment.
Thanks,
Faraz Shahbazker
Changelog:
elf/
* elf.h
(R_MIPS_IRELATIVE): New relocation type.
(R_MIPS_NUM): Bump up to 129.
(DT_MIPS_GENERAL_GOTNO): New dynamic tags.
(DT_MIPS_NUM): Bump to 0x37.
sysdeps/mips
* dl-irel.h: New file.
(elf_ifunc_invoke): New function.
(elf_irel): Likewise.
* dl-machine.h
Include new dl-irel.h
(ELF_MACHINE_BEFORE_RTLD_RELOC): Use DT_MIPS_GENERAL_GOTNO tag, if
present, to find the start of the normally relocated GOT.
(elf_machine_reloc): Add skip_ifunc to parameter.
Add case for R_MIPS_IRELATIVE. Modify REL32 to check for pre-emption
in case symbol is IFUNC and perform IFUNC indirection.
(elf_machine_rel): Add skip_ifunc to call to elf_machine_reloc().
(elf_machine_rela):Add skip_ifunc to call to elf_machine_reloc().
(RESOLVE_GOTSYM): Add check for STT_GNU_IFUNC.
(elf_machine_got_rel): Add check for STT_GNU_IFUNC. Use
DT_MIPS_GENERAL_GOTNO tag, if present, to find the start of the
normally relocated GOT. Skip normal GOT relocation for global GOT
entries corresponding to IFUNCs.
* dl-trampoline.c:
(__dl_runtime_resolve): Add check for STT_GNU_IFUNC.
---
elf/elf.h | 6 ++-
sysdeps/mips/dl-irel.h | 63 +++++++++++++++++++++++++++++++
sysdeps/mips/dl-machine.h | 86 ++++++++++++++++++++++++++++++++++++------
sysdeps/mips/dl-trampoline.c | 4 ++
4 files changed, 145 insertions(+), 14 deletions(-)
create mode 100644 sysdeps/mips/dl-irel.h
diff --git a/elf/elf.h b/elf/elf.h
index fbadda4..cfcf72c 100644
--- a/elf/elf.h
+++ b/elf/elf.h
@@ -1653,8 +1653,9 @@ typedef struct
#define R_MIPS_GLOB_DAT 51
#define R_MIPS_COPY 126
#define R_MIPS_JUMP_SLOT 127
+#define R_MIPS_IRELATIVE 128
/* Keep this the last entry. */
-#define R_MIPS_NUM 128
+#define R_MIPS_NUM 129
/* Legal values for p_type field of Elf32_Phdr. */
@@ -1731,7 +1732,8 @@ typedef struct
in a PIE as it stores a relative offset from the address of the tag
rather than an absolute address. */
#define DT_MIPS_RLD_MAP_REL 0x70000035
-#define DT_MIPS_NUM 0x36
+#define DT_MIPS_GENERAL_GOTNO 0x70000036 /* Number of relocated GOT entries */
+#define DT_MIPS_NUM 0x37
/* Legal values for DT_MIPS_FLAGS Elf32_Dyn entry. */
diff --git a/sysdeps/mips/dl-irel.h b/sysdeps/mips/dl-irel.h
new file mode 100644
index 0000000..7e1fdc4
--- /dev/null
+++ b/sysdeps/mips/dl-irel.h
@@ -0,0 +1,63 @@
+/* Machine-dependent ELF indirect relocation inline functions.
+ MIPS version.
+ Copyright (C) 2015 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
+ <http://www.gnu.org/licenses/>. */
+
+#ifndef _DL_IREL_H
+#define _DL_IREL_H
+
+#include <stdio.h>
+#include <unistd.h>
+#include <sgidefs.h>
+#include <link.h>
+#include <elf.h>
+#include <ldsodefs.h>
+
+#define ELF_MACHINE_IREL 1
+
+static inline ElfW(Addr)
+__attribute ((always_inline))
+elf_ifunc_invoke (ElfW(Addr) addr)
+{
+ /* Print some debugging info if wanted. */
+ if (__builtin_expect (GLRO(dl_debug_mask) & DL_DEBUG_SYMBOLS, 0))
+ {
+ ElfW(Addr) t_addr =
+ ((ElfW(Addr) (*) (unsigned long int)) (addr)) (GLRO(dl_hwcap));
+ GLRO(dl_debug_printf) ("In elf_ifunc_invoke(0x%lx), return(0x%lx)\n",
+ (unsigned long int)addr,
+ (unsigned long int)t_addr);
+ }
+
+ return ((ElfW(Addr) (*) (unsigned long int)) (addr)) (GLRO(dl_hwcap));
+}
+
+/* Allow either R_MIPS_RELATIVE or the nop R_MIPS_NONE. */
+static inline void
+__attribute ((always_inline))
+elf_irel (const ElfW(Rel) *reloc)
+{
+ ElfW(Addr) *const reloc_addr = (void *) reloc->r_offset;
+ const unsigned long int r_type = ELFW(R_TYPE) (reloc->r_info);
+
+ if (__builtin_expect (r_type == R_MIPS_IRELATIVE, 1))
+ *reloc_addr = elf_ifunc_invoke (*reloc_addr);
+ else if (r_type)
+ __libc_fatal ("unexpected reloc type in static binary");
+}
+
+#endif /* dl-irel.h */
diff --git a/sysdeps/mips/dl-machine.h b/sysdeps/mips/dl-machine.h
index 8738564..e7e0dc4 100644
--- a/sysdeps/mips/dl-machine.h
+++ b/sysdeps/mips/dl-machine.h
@@ -33,6 +33,7 @@
#include <sysdep.h>
#include <sys/asm.h>
#include <dl-tls.h>
+#include <dl-irel.h>
/* The offset of gp from GOT might be system-dependent. It's set by
ld. The same value is also */
@@ -200,10 +201,13 @@ do { \
if (__builtin_expect (map->l_addr == 0, 1)) \
break; \
\
- /* got[0] is reserved. got[1] is also reserved for the dynamic object \
- generated by gnu ld. Skip these reserved entries from \
- relocation. */ \
- i = (got[1] & ELF_MIPS_GNU_GOT1_MASK)? 2 : 1; \
+ if (__glibc_unlikely (map->l_info[DT_MIPS (GENERAL_GOTNO)] != NULL)) \
+ i = map->l_info[DT_MIPS (GENERAL_GOTNO)]->d_un.d_val; \
+ else \
+ /* got[0] is reserved. got[1] is also reserved for the dynamic \
+ object generated by gnu ld. Skip these reserved entries from \
+ relocation. */ \
+ i = (got[1] & ELF_MIPS_GNU_GOT1_MASK)? 2 : 1; \
n = map->l_info[DT_MIPS (LOCAL_GOTNO)]->d_un.d_val; \
\
/* Add the run-time displacement to all local got entries. */ \
@@ -493,7 +497,8 @@ auto inline void
__attribute__ ((always_inline))
elf_machine_reloc (struct link_map *map, ElfW(Addr) r_info,
const ElfW(Sym) *sym, const struct r_found_version *version,
- void *reloc_addr, ElfW(Addr) r_addend, int inplace_p)
+ void *reloc_addr, ElfW(Addr) r_addend, int inplace_p,
+ int skip_ifunc)
{
const unsigned long int r_type = ELFW(R_TYPE) (r_info);
ElfW(Addr) *addr_field = (ElfW(Addr) *) reloc_addr;
@@ -599,6 +604,41 @@ elf_machine_reloc (struct link_map *map, ElfW(Addr) r_info,
#endif
reloc_value += sym->st_value + map->l_addr;
}
+#ifndef RTLD_BOOTSTRAP
+ /* Resolve IFUNC symbols with pre-emption. */
+ else if (sym
+ && __glibc_unlikely (ELFW(ST_TYPE) (sym->st_info)
+ == STT_GNU_IFUNC)
+ && !skip_ifunc)
+ {
+ struct link_map *rmap = RESOLVE_MAP (&sym, version, r_type);
+
+ /* Symbol pre-empted, use value from GOT.
+ 2nd part of condition is redundant, explicit for clarity. */
+ if (__glibc_unlikely (rmap->l_relocated)
+ && __glibc_unlikely (rmap != map))
+ {
+ const ElfW(Addr) *got
+ = (const ElfW(Addr) *) D_PTR (rmap, l_info[DT_PLTGOT]);
+ const ElfW(Word) local_gotno
+ = (const ElfW(Word))
+ rmap->l_info[DT_MIPS (LOCAL_GOTNO)]->d_un.d_val;
+ symidx = (sym
+ - (ElfW(Sym) *) D_PTR(rmap, l_info[DT_SYMTAB]))
+ / sizeof (sym);
+ reloc_value = got[symidx + local_gotno - gotsym];
+ }
+ /* Symbol pre-empted by not yet relocated, use best guess. */
+ else if (__glibc_unlikely (rmap != map))
+ reloc_value = sym->st_value + rmap->l_addr;
+ /* Resolve IFUNC in this link unit. */
+ else if (__glibc_likely (ELFW(ST_TYPE) (sym->st_info)
+ == STT_GNU_IFUNC))
+ reloc_value = elf_ifunc_invoke (sym->st_value + map->l_addr);
+ else
+ reloc_value += sym->st_value + map->l_addr;
+ }
+#endif
else
{
#ifndef RTLD_BOOTSTRAP
@@ -698,6 +738,14 @@ elf_machine_reloc (struct link_map *map, ElfW(Addr) r_info,
break;
}
+ case R_MIPS_IRELATIVE:
+ /* The resolver routine is the symbol referenced by this relocation.
+ To get the address of the function to use at runtime, the resolver
+ routine is called and its return value is the address of the target
+ functon which is final relocation value. */
+ *addr_field = elf_ifunc_invoke (map->l_addr + *addr_field);
+ break;
+
#if _MIPS_SIM == _ABI64
case R_MIPS_64:
/* For full compliance with the ELF64 ABI, one must precede the
@@ -727,7 +775,8 @@ elf_machine_rel (struct link_map *map, const ElfW(Rel) *reloc,
const ElfW(Sym) *sym, const struct r_found_version *version,
void *const reloc_addr, int skip_ifunc)
{
- elf_machine_reloc (map, reloc->r_info, sym, version, reloc_addr, 0, 1);
+ elf_machine_reloc (map, reloc->r_info, sym, version, reloc_addr, 0, 1,
+ skip_ifunc);
}
auto inline void
@@ -768,7 +817,7 @@ elf_machine_rela (struct link_map *map, const ElfW(Rela) *reloc,
void *const reloc_addr, int skip_ifunc)
{
elf_machine_reloc (map, reloc->r_info, sym, version, reloc_addr,
- reloc->r_addend, 0);
+ reloc->r_addend, 0, skip_ifunc);
}
auto inline void
@@ -795,8 +844,18 @@ elf_machine_got_rel (struct link_map *map, int lazy)
const struct r_found_version *version __attribute__ ((unused)) \
= vernum ? &map->l_versions[vernum[sym_index] & 0x7fff] : NULL; \
struct link_map *sym_map; \
+ ElfW(Addr) value = 0; \
sym_map = RESOLVE_MAP (&ref, version, reloc); \
- ref ? sym_map->l_addr + ref->st_value : 0; \
+ if (__glibc_likely(ref != NULL)) \
+ { \
+ value = sym_map->l_addr + ref->st_value; \
+ if (__glibc_unlikely (ELFW(ST_TYPE) (ref->st_info) \
+ == STT_GNU_IFUNC \
+ && sym_map != map \
+ && sym_map->l_relocated)) \
+ value = elf_ifunc_invoke (value); \
+ } \
+ value; \
})
if (map->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
@@ -810,9 +869,12 @@ elf_machine_got_rel (struct link_map *map, int lazy)
/* The dynamic linker's local got entries have already been relocated. */
if (map != &GL(dl_rtld_map))
{
- /* got[0] is reserved. got[1] is also reserved for the dynamic object
- generated by gnu ld. Skip these reserved entries from relocation. */
- i = (got[1] & ELF_MIPS_GNU_GOT1_MASK)? 2 : 1;
+ if (__glibc_unlikely(map->l_info[DT_MIPS (GENERAL_GOTNO)] != NULL))
+ i = map->l_info[DT_MIPS (GENERAL_GOTNO)]->d_un.d_val;
+ else
+ /* got[0] is reserved. got[1] is also reserved for the dynamic object
+ generated by gnu ld. Skip these reserved entries from relocation. */
+ i = (got[1] & ELF_MIPS_GNU_GOT1_MASK)? 2 : 1;
/* Add the run-time displacement to all local got entries if
needed. */
@@ -866,7 +928,7 @@ elf_machine_got_rel (struct link_map *map, int lazy)
if (sym->st_other == 0)
*got += map->l_addr;
}
- else
+ else if (ELFW(ST_TYPE) (sym->st_info) != STT_GNU_IFUNC)
*got = RESOLVE_GOTSYM (sym, vernum, symidx, R_MIPS_32);
++got;
diff --git a/sysdeps/mips/dl-trampoline.c b/sysdeps/mips/dl-trampoline.c
index 25b1709..d5f8891 100644
--- a/sysdeps/mips/dl-trampoline.c
+++ b/sysdeps/mips/dl-trampoline.c
@@ -193,6 +193,10 @@ __dl_runtime_resolve (ElfW(Word) sym_index,
/* Currently value contains the base load address of the object
that defines sym. Now add in the symbol offset. */
value = (sym ? sym_map->l_addr + sym->st_value : 0);
+ if (sym != NULL
+ && __builtin_expect (ELFW(ST_TYPE) (sym->st_info)
+ == STT_GNU_IFUNC, 0))
+ value = elf_ifunc_invoke (DL_FIXUP_VALUE_ADDR (value));
}
else
/* We already found the symbol. The module (and therefore its load
--
1.7.9.5
Attachment:
Spec.txt
Description: Spec.txt
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