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authorFangrui Song <maskray@google.com>2022-03-08 17:17:05 -0800
committerFangrui Song <maskray@google.com>2022-03-08 17:17:05 -0800
commit1c6cc29baf9a4c7129ab2e94b0d4022bfa4f3299 (patch)
tree008312335cd84ecfcc73c38b72ba836d06e3ca2f
parentedc696a73a7cb07b1aa68792a845a98d036ee7eb (diff)
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glibc-maskray/relr.tar.gz
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elf: Support DT_RELR relative relocation format [BZ #27924]maskray/relr
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.
-rwxr-xr-xconfigure37
-rw-r--r--configure.ac4
-rw-r--r--elf/Makefile7
-rw-r--r--elf/dynamic-link.h34
-rw-r--r--elf/elf.h13
-rw-r--r--elf/get-dynamic-info.h3
-rw-r--r--elf/tst-relr-no-pie.c1
-rw-r--r--elf/tst-relr.c45
8 files changed, 142 insertions, 2 deletions
diff --git a/configure b/configure
index 8e5bee7..c4e0d9e 100755
--- a/configure
+++ b/configure
@@ -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
$as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
libc_linker_feature=no
diff --git a/configure.ac b/configure.ac
index 87f67d2..d6bb323 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1367,6 +1367,10 @@ LIBC_LINKER_FEATURE([--depaudit], [-Wl,--depaudit,x],
[libc_cv_depaudit=yes], [libc_cv_depaudit=no])
LIBC_CONFIG_VAR([have-depaudit], [$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], [$libc_cv_relr])
+
LIBC_LINKER_FEATURE([--no-dynamic-linker],
[-Wl,--no-dynamic-linker],
[libc_cv_no_dynamic_linker=yes],
diff --git a/elf/Makefile b/elf/Makefile
index c96924e..d75353e 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -541,6 +541,13 @@ tests-special += \
# tests-special
endif
endif
+ifeq ($(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)
diff --git a/elf/dynamic-link.h b/elf/dynamic-link.h
index 25dd7ca..169745f 100644
--- a/elf/dynamic-link.h
+++ b/elf/dynamic-link.h
@@ -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)
diff --git a/elf/elf.h b/elf/elf.h
index 0735f6b..0195029 100644
--- a/elf/elf.h
+++ b/elf/elf.h
@@ -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 */
diff --git a/elf/get-dynamic-info.h b/elf/get-dynamic-info.h
index 6c2ccd6..6c2a3a1 100644
--- a/elf/get-dynamic-info.h
+++ b/elf/get-dynamic-info.h
@@ -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);
diff --git a/elf/tst-relr-no-pie.c b/elf/tst-relr-no-pie.c
new file mode 100644
index 0000000..7df0cdb
--- /dev/null
+++ b/elf/tst-relr-no-pie.c
@@ -0,0 +1 @@
+#include "tst-relr.c"
diff --git a/elf/tst-relr.c b/elf/tst-relr.c
new file mode 100644
index 0000000..0b0fe5e
--- /dev/null
+++ b/elf/tst-relr.c
@@ -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>