diff --git a/sysdeps/aarch64/Makefile b/sysdeps/aarch64/Makefile
index 141d7d9cc2..74479604f2 100644
--- a/sysdeps/aarch64/Makefile
+++ b/sysdeps/aarch64/Makefile
@@ -9,7 +9,9 @@ LDFLAGS-rtld += -Wl,-z,force-bti,--fatal-warnings
endif
ifeq ($(subdir),elf)
-sysdep-dl-routines += dl-bti
+sysdep-dl-routines += \
+ dl-bti \
+ dl-gcs
tests += tst-audit26 \
tst-audit27
@@ -35,7 +37,9 @@ endif
ifeq ($(subdir),elf)
sysdep-rtld-routines += dl-start
sysdep-dl-routines += tlsdesc dl-tlsdesc
-gen-as-const-headers += dl-link.sym
+gen-as-const-headers += \
+ dl-link.sym \
+ rtld-global-offsets.sym
tests-internal += tst-ifunc-arg-1 tst-ifunc-arg-2
diff --git a/sysdeps/aarch64/dl-gcs.c b/sysdeps/aarch64/dl-gcs.c
new file mode 100644
index 0000000000..870336f2bb
--- /dev/null
+++ b/sysdeps/aarch64/dl-gcs.c
@@ -0,0 +1,25 @@
+/* AArch64 GCS functions.
+ Copyright (C) 2024-2025 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
+ 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
+ . */
+
+#include
+
+/* Used to report error when prctl system call to enabled GCS fails. */
+
+void _dl_gcs_enable_failed (int code)
+{
+ _dl_fatal_printf ("failed to enable GCS: %d\n", -code);
+}
diff --git a/sysdeps/aarch64/dl-start.S b/sysdeps/aarch64/dl-start.S
index 3b8eff0acd..a249fda21c 100644
--- a/sysdeps/aarch64/dl-start.S
+++ b/sysdeps/aarch64/dl-start.S
@@ -18,6 +18,7 @@
. */
#include
+#include
ENTRY (_start)
/* Create an initial frame with 0 LR and FP */
@@ -25,11 +26,33 @@ ENTRY (_start)
mov x29, #0
mov x30, #0
+ /* Load and relocate all library dependencies. */
mov x0, sp
PTR_ARG (0)
bl _dl_start
/* Returns user entry point in x0. */
mov PTR_REG (21), PTR_REG (0)
+
+ /* Use GL(dl_aarch64_gcs) to set the shadow stack status. */
+ adrp x16, _rtld_local
+ add PTR_REG (16), PTR_REG (16), :lo12:_rtld_local
+ ldr x1, [x16, GL_DL_AARCH64_GCS_OFFSET]
+ cbz x1, L(skip_gcs_enable)
+
+ /* Enable GCS before user code runs. Note that IFUNC resolvers and
+ LD_AUDIT hooks may run before, but should not create threads. */
+#define PR_SET_SHADOW_STACK_STATUS 75
+#define PR_SHADOW_STACK_ENABLE (1UL << 0)
+ mov x0, PR_SET_SHADOW_STACK_STATUS
+ mov x1, PR_SHADOW_STACK_ENABLE
+ mov x2, 0
+ mov x3, 0
+ mov x4, 0
+ mov x8, #SYS_ify(prctl)
+ svc 0x0
+ cbnz w0, L(failed_gcs_enable)
+L(skip_gcs_enable):
+
.globl _dl_start_user
.type _dl_start_user, %function
_dl_start_user:
@@ -40,14 +63,17 @@ _dl_start_user:
/* Compute envp. */
add PTR_REG (3), PTR_REG (2), PTR_REG (1), lsl PTR_LOG_SIZE
add PTR_REG (3), PTR_REG (3), PTR_SIZE
- adrp x16, _rtld_local
- add PTR_REG (16), PTR_REG (16), :lo12:_rtld_local
+ /* Run the init functions of the loaded modules. */
ldr PTR_REG (0), [x16]
bl _dl_init
/* Load the finalizer function. */
adrp x0, _dl_fini
add PTR_REG (0), PTR_REG (0), :lo12:_dl_fini
/* Jump to the user's entry point. */
- mov x16, x21
- br x16
+ mov x16, x21
+ br x16
+
+L(failed_gcs_enable):
+ b _dl_gcs_enable_failed
+
END (_start)
diff --git a/sysdeps/aarch64/rtld-global-offsets.sym b/sysdeps/aarch64/rtld-global-offsets.sym
index 23cdaf7d9e..6c0690bb95 100644
--- a/sysdeps/aarch64/rtld-global-offsets.sym
+++ b/sysdeps/aarch64/rtld-global-offsets.sym
@@ -3,8 +3,13 @@
#include
#define GLRO_offsetof(name) offsetof (struct rtld_global_ro, _##name)
+#define GL_offsetof(name) offsetof (struct rtld_global, _##name)
-- Offsets of _rtld_global_ro in libc.so
GLRO_DL_HWCAP_OFFSET GLRO_offsetof (dl_hwcap)
GLRO_DL_HWCAP2_OFFSET GLRO_offsetof (dl_hwcap2)
+
+-- Offsets of _rtld_global in libc.so
+
+GL_DL_AARCH64_GCS_OFFSET GL_offsetof (dl_aarch64_gcs)