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elf: Support DT_RELR relative relocation format [BZ #27924] 

PIE and shared objects usually have many relative relocations. In
2017/2018, SHT_RELR/DT_RELR was proposed on
https://groups.google.com/g/generic-abi/c/bX460iggiKg/m/GxjM0L-PBAAJ
("Proposal for a new section type SHT_RELR") and is a pre-standard. RELR
usually takes 3% or smaller space than R_*_RELATIVE relocations. The
virtual memory size of a mostly statically linked PIE is typically 5~10%
smaller.

This patch adds ELF_DYNAMIC_DO_RELR to ELF_DYNAMIC_RELOCATE.
ELF_DYNAMIC_DO_RELR is ordered before ELF_DYNAMIC_DO_REL[A] so that ifunc
resolvers that require relocated got entries have them relocated. This is
needed for ppc64 according to Alan Modra.
This commit is contained in:
Fangrui Song 2022-03-08 17:17:05 -08:00
parent edc696a73a
commit 1c6cc29baf
8 changed files with 142 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

37
configure vendored
View File

@ -6115,6 +6115,43 @@ $as_echo "$libc_linker_feature" >&6; }
config_vars="$config_vars
have-depaudit = $libc_cv_depaudit"
{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports -z pack-relative-relocs" >&5
$as_echo_n "checking for linker that supports -z pack-relative-relocs... " >&6; }
libc_linker_feature=no
if test x"$gnu_ld" = x"yes"; then
cat > conftest.c <<EOF
int _start (void) { return 42; }
EOF
if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
-Wl,-z,pack-relative-relocs -nostdlib -nostartfiles
-fPIC -shared -o conftest.so conftest.c
1>&5'
{ { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
(eval $ac_try) 2>&5
ac_status=$?
$as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
test $ac_status = 0; }; }
then
if ${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp -Wl,-z,pack-relative-relocs -nostdlib \
-nostartfiles -fPIC -shared -o conftest.so conftest.c 2>&1 \
| grep "warning: -z pack-relative-relocs ignored" > /dev/null 2>&1; then
true
else
libc_linker_feature=yes
fi
fi
rm -f conftest*
fi
if test $libc_linker_feature = yes; then
libc_cv_relr=yes
else
libc_cv_relr=no
fi
{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
$as_echo "$libc_linker_feature" >&6; }
config_vars="$config_vars
have-relr = $libc_cv_relr"
{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5
$as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
libc_linker_feature=no

4
configure.ac
View File

@ -1367,6 +1367,10 @@ LIBC_LINKER_FEATURE([--depaudit], [-Wl,--depaudit,x],
[libc_cv_depaudit=yes], [libc_cv_depaudit=no])
LIBC_CONFIG_VAR([have-depaudit], [$libc_cv_depaudit])
LIBC_LINKER_FEATURE([-z pack-relative-relocs], [-Wl,-z,pack-relative-relocs],
[libc_cv_relr=yes], [libc_cv_relr=no])
LIBC_CONFIG_VAR([have-relr], [$libc_cv_relr])
LIBC_LINKER_FEATURE([--no-dynamic-linker],
[-Wl,--no-dynamic-linker],
[libc_cv_no_dynamic_linker=yes],

7
elf/Makefile
View File

@ -541,6 +541,13 @@ tests-special += \
# tests-special
endif
endif
ifeq ($(have-relr),yes)
tests += tst-relr tst-relr-no-pie
tests-pie += tst-relr
tests-no-pie += tst-relr-no-pie
LDFLAGS-tst-relr += -z pack-relative-relocs
LDFLAGS-tst-relr-no-pie += -z pack-relative-relocs
endif
endif
ifeq ($(run-built-tests),yes)

34
elf/dynamic-link.h
View File

@ -146,12 +146,46 @@ elf_machine_lazy_rel (struct link_map *map, struct r_scope_elem *scope[],
# define ELF_DYNAMIC_DO_RELA(map, scope, lazy, skip_ifunc) /* Nothing to do. */
# endif
# define ELF_DYNAMIC_DO_RELR(map) \
do { \
ElfW(Addr) l_addr = (map)->l_addr, *where = 0; \
const ElfW(Relr) *r, *end; \
if (!(map)->l_info[DT_RELR]) \
break; \
r = (const ElfW(Relr) *)D_PTR((map), l_info[DT_RELR]); \
end = (const ElfW(Relr) *)((const char *)r + \
(map)->l_info[DT_RELRSZ]->d_un.d_val); \
for (; r < end; r++) \
{ \
ElfW(Relr) entry = *r; \
if ((entry & 1) == 0) \
{ \
where = (ElfW(Addr) *)(l_addr + entry); \
*where++ += l_addr; \
} \
else \
{ \
for (long i = 0; (entry >>= 1) != 0; i++) \
if ((entry & 1) != 0) \
where[i] += l_addr; \
where += CHAR_BIT * sizeof(ElfW(Relr)) - 1; \
} \
} \
} while (0);
/* This can't just be an inline function because GCC is too dumb
to inline functions containing inlines themselves. */
# ifdef RTLD_BOOTSTRAP
# define DO_RTLD_BOOTSTRAP 1
# else
# define DO_RTLD_BOOTSTRAP 0
# endif
# define ELF_DYNAMIC_RELOCATE(map, scope, lazy, consider_profile, skip_ifunc) \
do { \
int edr_lazy = elf_machine_runtime_setup ((map), (scope), (lazy), \
(consider_profile)); \
if ((map) != &GL(dl_rtld_map) || DO_RTLD_BOOTSTRAP) \
ELF_DYNAMIC_DO_RELR (map); \
ELF_DYNAMIC_DO_REL ((map), (scope), edr_lazy, skip_ifunc); \
ELF_DYNAMIC_DO_RELA ((map), (scope), edr_lazy, skip_ifunc); \
} while (0)

13
elf/elf.h
View File

@ -443,7 +443,8 @@ typedef struct
#define SHT_PREINIT_ARRAY 16 /* Array of pre-constructors */
#define SHT_GROUP 17 /* Section group */
#define SHT_SYMTAB_SHNDX 18 /* Extended section indices */
#define SHT_NUM 19 /* Number of defined types. */
#define SHT_RELR 19 /* RELR relative relocations */
#define SHT_NUM 20 /* Number of defined types. */
#define SHT_LOOS 0x60000000 /* Start OS-specific. */
#define SHT_GNU_ATTRIBUTES 0x6ffffff5 /* Object attributes. */
#define SHT_GNU_HASH 0x6ffffff6 /* GNU-style hash table. */
@ -662,6 +663,11 @@ typedef struct
Elf64_Sxword r_addend; /* Addend */
} Elf64_Rela;
/* RELR relocation table entry */
typedef Elf32_Word Elf32_Relr;
typedef Elf64_Xword Elf64_Relr;
/* How to extract and insert information held in the r_info field. */
#define ELF32_R_SYM(val) ((val) >> 8)
@ -887,7 +893,10 @@ typedef struct
#define DT_PREINIT_ARRAY 32 /* Array with addresses of preinit fct*/
#define DT_PREINIT_ARRAYSZ 33 /* size in bytes of DT_PREINIT_ARRAY */
#define DT_SYMTAB_SHNDX 34 /* Address of SYMTAB_SHNDX section */
#define DT_NUM 35 /* Number used */
#define DT_RELRSZ 35 /* Total size of RELR relative relocations */
#define DT_RELR 36 /* Address of RELR relative relocations */
#define DT_RELRENT 37 /* Size of one RELR relative relocaction */
#define DT_NUM 38 /* Number used */
#define DT_LOOS 0x6000000d /* Start of OS-specific */
#define DT_HIOS 0x6ffff000 /* End of OS-specific */
#define DT_LOPROC 0x70000000 /* Start of processor-specific */

3
elf/get-dynamic-info.h
View File

@ -89,6 +89,7 @@ elf_get_dynamic_info (struct link_map *l, bool bootstrap,
# if ! ELF_MACHINE_NO_REL
ADJUST_DYN_INFO (DT_REL);
# endif
ADJUST_DYN_INFO (DT_RELR);
ADJUST_DYN_INFO (DT_JMPREL);
ADJUST_DYN_INFO (VERSYMIDX (DT_VERSYM));
ADJUST_DYN_INFO (ADDRIDX (DT_GNU_HASH));
@ -113,6 +114,8 @@ elf_get_dynamic_info (struct link_map *l, bool bootstrap,
if (info[DT_REL] != NULL)
assert (info[DT_RELENT]->d_un.d_val == sizeof (ElfW(Rel)));
#endif
if (info[DT_RELR] != NULL)
assert (info[DT_RELRENT]->d_un.d_val == sizeof (ElfW(Relr)));
if (bootstrap || static_pie_bootstrap)
{
assert (info[DT_RUNPATH] == NULL);

1
elf/tst-relr-no-pie.c Normal file
View File

@ -0,0 +1 @@
#include "tst-relr.c"

45
elf/tst-relr.c Normal file
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@ -0,0 +1,45 @@
#include <link.h>
#include <stdbool.h>
#include <stdio.h>
static int o, x;
#define ELEMS O O O O O O O O X X X X X X X O O X O O X X X E X E E O X O E
#define E 0,
#define O &o,
#define X &x,
void *arr[] = { ELEMS };
#undef O
#undef X
#define O 1,
#define X 2,
static char val[] = { ELEMS };
static int
do_test (void)
{
ElfW(Dyn) *d = _DYNAMIC;
if (d)
{
bool has_relr = false;
for (; d->d_tag != DT_NULL; d++)
if (d->d_tag == DT_RELR)
has_relr = true;
if (!has_relr)
{
fprintf (stderr, "no DT_RELR\n");
return 1;
}
}
for (int i = 0; i < sizeof (arr) / sizeof (arr[0]); i++)
if (!((arr[i] == 0 && val[i] == 0) ||
(arr[i] == &o && val[i] == 1) ||
(arr[i] == &x && val[i] == 2)))
return 1;
return 0;
}
#include <support/test-driver.c>