arm: Update _dl_tlsdesc_dynamic to preserve caller-saved registers (BZ 31372)

ARM _dl_tlsdesc_dynamic slow path has two issues:

  * The ip/r12 is defined by AAPCS as a scratch register, and gcc is
    used to save the stack pointer before on some function calls.  So it
    should also be saved/restored as well.  It fixes the tst-gnu2-tls2.

  * None of the possible VFP registers are saved/restored.  ARM has the
    additional complexity to have different VFP bank sizes (depending of
    VFP support by the chip).

The tst-gnu2-tls2 test is extended to check for VFP registers, although
only for hardfp builds.  Different than setcontext, _dl_tlsdesc_dynamic
does not have  HWCAP_ARM_IWMMXT (I don't have a way to properly test
it and it is almost a decade since newer hardware was released).

With this patch there is no need to mark tst-gnu2-tls2 as XFAIL.

Checked on arm-linux-gnueabihf.
Reviewed-by: H.J. Lu <hjl.tools@gmail.com>

(cherry picked from commit 64c7e34428)

config.h.in

@@ -141,6 +141,9 @@
 /* LOONGARCH floating-point ABI for ld.so.  */
 #undef LOONGARCH_ABI_FRLEN
 
+/* Define whether ARM used hard-float and support VFPvX-D32.  */
+#undef HAVE_ARM_PCS_VFP_D32
+
 /* Linux specific: minimum supported kernel version.  */
 #undef	__LINUX_KERNEL_VERSION
 

elf/Makefile

@@ -3056,10 +3056,6 @@ $(objpfx)tst-gnu2-tls2.out: \
   $(objpfx)tst-gnu2-tls2mod2.so
 
 ifeq (yes,$(have-mtls-dialect-gnu2))
-# This test fails if dl_tlsdesc_dynamic doesn't preserve all caller-saved
-# registers.  See https://sourceware.org/bugzilla/show_bug.cgi?id=31372
-test-xfail-tst-gnu2-tls2 = yes
-
 CFLAGS-tst-tlsgap-mod0.c += -mtls-dialect=gnu2
 CFLAGS-tst-tlsgap-mod1.c += -mtls-dialect=gnu2
 CFLAGS-tst-tlsgap-mod2.c += -mtls-dialect=gnu2

elf/tst-gnu2-tls2.h

@@ -27,6 +27,10 @@ extern struct tls *apply_tls (struct tls *);
 
 /* An architecture can define them to verify that clobber caller-saved
    registers aren't changed by the implicit TLSDESC call.  */
+#ifndef INIT_TLSDESC_CALL
+# define INIT_TLSDESC_CALL()
+#endif
+
 #ifndef BEFORE_TLSDESC_CALL
 # define BEFORE_TLSDESC_CALL()
 #endif

elf/tst-gnu2-tls2mod0.c

@@ -16,13 +16,14 @@
    License along with the GNU C Library; if not, see
    <https://www.gnu.org/licenses/>.  */
 
-#include "tst-gnu2-tls2.h"
+#include <tst-gnu2-tls2.h>
 
 __thread struct tls tls_var0 __attribute__ ((visibility ("hidden")));
 
 struct tls *
 apply_tls (struct tls *p)
 {
+  INIT_TLSDESC_CALL ();
   BEFORE_TLSDESC_CALL ();
   tls_var0 = *p;
   struct tls *ret = &tls_var0;

elf/tst-gnu2-tls2mod1.c

@@ -16,13 +16,14 @@
    License along with the GNU C Library; if not, see
    <https://www.gnu.org/licenses/>.  */
 
-#include "tst-gnu2-tls2.h"
+#include <tst-gnu2-tls2.h>
 
 __thread struct tls tls_var1[100] __attribute__ ((visibility ("hidden")));
 
 struct tls *
 apply_tls (struct tls *p)
 {
+  INIT_TLSDESC_CALL ();
   BEFORE_TLSDESC_CALL ();
   tls_var1[1] = *p;
   struct tls *ret = &tls_var1[1];

elf/tst-gnu2-tls2mod2.c

@@ -16,13 +16,14 @@
    License along with the GNU C Library; if not, see
    <https://www.gnu.org/licenses/>.  */
 
-#include "tst-gnu2-tls2.h"
+#include <tst-gnu2-tls2.h>
 
 __thread struct tls tls_var2 __attribute__ ((visibility ("hidden")));
 
 struct tls *
 apply_tls (struct tls *p)
 {
+  INIT_TLSDESC_CALL ();
   BEFORE_TLSDESC_CALL ();
   tls_var2 = *p;
   struct tls *ret = &tls_var2;

sysdeps/arm/configure

@@ -187,6 +187,38 @@ else
 default-abi = soft"
 fi
 
+{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking whether VFP supports 32 registers" >&5
+printf %s "checking whether VFP supports 32 registers... " >&6; }
+if test ${libc_cv_arm_pcs_vfp_d32+y}
+then :
+  printf %s "(cached) " >&6
+else $as_nop
+
+cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+void foo (void)
+{
+  asm volatile ("vldr d16,=17" : : : "d16");
+}
+
+_ACEOF
+if ac_fn_c_try_compile "$LINENO"
+then :
+  libc_cv_arm_pcs_vfp_d32=yes
+else $as_nop
+  libc_cv_arm_pcs_vfp_d32=no
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.beam conftest.$ac_ext
+fi
+{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: $libc_cv_arm_pcs_vfp_d32" >&5
+printf "%s\n" "$libc_cv_arm_pcs_vfp_d32" >&6; }
+if test "$libc_cv_arm_pcs_vfp_d32" = yes ;
+then
+  printf "%s\n" "#define HAVE_ARM_PCS_VFP_D32 1" >>confdefs.h
+
+fi
+
 { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking whether PC-relative relocs in movw/movt work properly" >&5
 printf %s "checking whether PC-relative relocs in movw/movt work properly... " >&6; }
 if test ${libc_cv_arm_pcrel_movw+y}

sysdeps/arm/configure.ac

@@ -21,6 +21,21 @@ else
   LIBC_CONFIG_VAR([default-abi], [soft])
 fi
 
+AC_CACHE_CHECK([whether VFP supports 32 registers],
+		libc_cv_arm_pcs_vfp_d32, [
+AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
+void foo (void)
+{
+  asm volatile ("vldr d16,=17" : : : "d16");
+}
+]])],
+                [libc_cv_arm_pcs_vfp_d32=yes],
+                [libc_cv_arm_pcs_vfp_d32=no])])
+if test "$libc_cv_arm_pcs_vfp_d32" = yes ;
+then
+  AC_DEFINE(HAVE_ARM_PCS_VFP_D32)
+fi
+
 AC_CACHE_CHECK([whether PC-relative relocs in movw/movt work properly],
 	       libc_cv_arm_pcrel_movw, [
 cat > conftest.s <<\EOF

sysdeps/arm/dl-tlsdesc.S

@@ -19,6 +19,7 @@
 #include <sysdep.h>
 #include <arm-features.h>
 #include <tls.h>
+#include <rtld-global-offsets.h>
 #include "tlsdesc.h"
 
 	.text
@@ -83,14 +84,20 @@ _dl_tlsdesc_dynamic(struct tlsdesc *tdp)
 	.align 2
 _dl_tlsdesc_dynamic:
 	/* Our calling convention is to clobber r0, r1 and the processor
-	   flags.  All others that are modified must be saved */
+	   flags.  All others that are modified must be saved.  r5 is
-	eabi_save ({r2,r3,r4,lr})
+	   used as the hwcap value to avoid reload after __tls_get_addr
-	push	{r2,r3,r4,lr}
+	   call.  If required we will save the vector register on the slow
-	cfi_adjust_cfa_offset (16)
+	   path.  */
+	eabi_save ({r2,r3,r4,r5,ip,lr})
+	push	{r2,r3,r4,r5,ip,lr}
+	cfi_adjust_cfa_offset (24)
 	cfi_rel_offset (r2,0)
 	cfi_rel_offset (r3,4)
 	cfi_rel_offset (r4,8)
-	cfi_rel_offset (lr,12)
+	cfi_rel_offset (r5,12)
+	cfi_rel_offset (ip,16)
+	cfi_rel_offset (lr,20)
+
 	ldr	r1, [r0] /* td */
 	GET_TLS (lr)
 	mov	r4, r0 /* r4 = tp */
@@ -113,22 +120,69 @@ _dl_tlsdesc_dynamic:
 	rsbne	r0, r4, r3
 	bne	2f
 1:	mov	r0, r1
+
+	/* Load the hwcap to check for vector support.  */
+	ldr     r2, 3f
+	ldr     r1, .Lrtld_global_ro
+0:	add     r2, pc, r2
+	ldr     r2, [r2, r1]
+	ldr     r5, [r2, #RTLD_GLOBAL_RO_DL_HWCAP_OFFSET]
+
+#ifdef __SOFTFP__
+	tst     r5, #HWCAP_ARM_VFP
+	beq     .Lno_vfp
+#endif
+
+	/* Store the VFP registers.  Don't use VFP instructions directly
+	   because this code is used in non-VFP multilibs.  */
+#define VFP_STACK_REQ (32*8 + 8)
+	sub	sp, sp, VFP_STACK_REQ
+	cfi_adjust_cfa_offset (VFP_STACK_REQ)
+	mov	r3, sp
+	.inst	0xeca30b20	/* vstmia r3!, {d0-d15} */
+	tst	r5, #HWCAP_ARM_VFPD32
+	beq	4f
+	.inst	0xece30b20	/* vstmia r3!, {d16-d31}  */
+	/* Store the floating-point status register.  */
+4:	.inst	0xeef12a10	/* vmrs	r2, fpscr */
+	str	r2, [r3]
+.Lno_vfp:
 	bl	__tls_get_addr
 	rsb	r0, r4, r0
+#ifdef __SOFTFP__
+	tst     r5, #HWCAP_ARM_VFP
+	beq     2f
+#endif
+	mov	r3, sp
+	.inst	0xecb30b20	/* vldmia r3!, {d0-d15}  */
+	tst	r5, #HWCAP_ARM_VFPD32
+	beq	5f
+	.inst	0xecf30b20	/* vldmia r3!, {d16-d31}  */
+	ldr	r4, [r3]
+5:	.inst	0xeee14a10	/* vmsr	fpscr, r4  */
+	add	sp, sp, VFP_STACK_REQ
+	cfi_adjust_cfa_offset (-VFP_STACK_REQ)
+
 2:
 #if ((defined (__ARM_ARCH_4T__) && defined (__THUMB_INTERWORK__)) \
      || defined (ARM_ALWAYS_BX))
-	pop	{r2,r3,r4, lr}
+	pop	{r2,r3,r4,r5,ip, lr}
-	cfi_adjust_cfa_offset (-16)
+	cfi_adjust_cfa_offset (-20)
 	cfi_restore (lr)
+	cfi_restore (ip)
+	cfi_restore (r5)
 	cfi_restore (r4)
 	cfi_restore (r3)
 	cfi_restore (r2)
 	bx	lr
 #else
-	pop	{r2,r3,r4, pc}
+	pop	{r2,r3,r4,r5,ip, pc}
 #endif
 	eabi_fnend
 	cfi_endproc
 	.size	_dl_tlsdesc_dynamic, .-_dl_tlsdesc_dynamic
+
+3:      .long   _GLOBAL_OFFSET_TABLE_ - 0b - PC_OFS
+.Lrtld_global_ro:
+	.long   C_SYMBOL_NAME(_rtld_global_ro)(GOT)
 #endif /* SHARED */

sysdeps/arm/tst-gnu2-tls2.h

@@ -0,0 +1,128 @@
+/* Test TLSDESC relocation.  ARM version.
+   Copyright (C) 2024 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/>.  */
+
+#include <config.h>
+#include <sys/auxv.h>
+#include <string.h>
+#include <stdlib.h>
+#include <endian.h>
+
+#ifndef __SOFTFP__
+
+# ifdef HAVE_ARM_PCS_VFP_D32
+#  define SAVE_VFP_D32					\
+      asm volatile ("vldr d16,=17" : : : "d16");	\
+      asm volatile ("vldr d17,=18" : : : "d17");	\
+      asm volatile ("vldr d18,=19" : : : "d18");	\
+      asm volatile ("vldr d19,=20" : : : "d19");	\
+      asm volatile ("vldr d20,=21" : : : "d20");	\
+      asm volatile ("vldr d21,=22" : : : "d21");	\
+      asm volatile ("vldr d22,=23" : : : "d22");	\
+      asm volatile ("vldr d23,=24" : : : "d23");	\
+      asm volatile ("vldr d24,=25" : : : "d24");	\
+      asm volatile ("vldr d25,=26" : : : "d25");	\
+      asm volatile ("vldr d26,=27" : : : "d26");	\
+      asm volatile ("vldr d27,=28" : : : "d27");	\
+      asm volatile ("vldr d28,=29" : : : "d28");	\
+      asm volatile ("vldr d29,=30" : : : "d29");	\
+      asm volatile ("vldr d30,=31" : : : "d30");	\
+      asm volatile ("vldr d31,=32" : : : "d31");
+# else
+#  define SAVE_VFP_D32
+# endif
+
+# define INIT_TLSDESC_CALL()				\
+  unsigned long hwcap = getauxval (AT_HWCAP)
+
+/* Set each vector register to a value from 1 to 32 before the TLS access,
+   dump to memory after TLS access, and compare with the expected values.  */
+
+# define BEFORE_TLSDESC_CALL()				\
+  if (hwcap & HWCAP_ARM_VFP)				\
+    {							\
+      asm volatile ("vldr  d0,=1" : : : "d0");		\
+      asm volatile ("vldr  d1,=2" : : : "d1");		\
+      asm volatile ("vldr  d2,=3" : : : "d1");		\
+      asm volatile ("vldr  d3,=4" : : : "d3");		\
+      asm volatile ("vldr  d4,=5" : : : "d4");		\
+      asm volatile ("vldr  d5,=6" : : : "d5");		\
+      asm volatile ("vldr  d6,=7" : : : "d6");		\
+      asm volatile ("vldr  d7,=8" : : : "d7");		\
+      asm volatile ("vldr  d8,=9" : : : "d8");		\
+      asm volatile ("vldr  d9,=10" : : : "d9");		\
+      asm volatile ("vldr d10,=11" : : : "d10");	\
+      asm volatile ("vldr d11,=12" : : : "d11");	\
+      asm volatile ("vldr d12,=13" : : : "d12");	\
+      asm volatile ("vldr d13,=14" : : : "d13");	\
+      asm volatile ("vldr d14,=15" : : : "d14");	\
+      asm volatile ("vldr d15,=16" : : : "d15");	\
+    }							\
+  if (hwcap & HWCAP_ARM_VFPD32)				\
+    {							\
+      SAVE_VFP_D32					\
+    }
+
+# define VFP_STACK_REQ (16*8)
+# if __BYTE_ORDER == __BIG_ENDIAN
+#  define DISP 7
+# else
+#  define DISP 0
+# endif
+
+# ifdef HAVE_ARM_PCS_VFP_D32
+#  define CHECK_VFP_D32							\
+      char vfp[VFP_STACK_REQ];						\
+      asm volatile ("vstmia %0, {d16-d31}\n"				\
+		    :							\
+		    : "r" (vfp)						\
+		    : "memory");					\
+									\
+      char expected[VFP_STACK_REQ] = { 0 };				\
+      for (int i = 0; i < 16; ++i)					\
+	expected[i * 8 + DISP] = i + 17;				\
+									\
+      if (memcmp (vfp, expected, VFP_STACK_REQ) != 0)			\
+        abort ();
+# else
+#  define CHECK_VFP_D32
+# endif
+
+# define AFTER_TLSDESC_CALL()						\
+  if (hwcap & HWCAP_ARM_VFP)						\
+    {									\
+      char vfp[VFP_STACK_REQ];						\
+      asm volatile ("vstmia %0, {d0-d15}\n"				\
+		    :							\
+		    : "r" (vfp)						\
+		    : "memory");					\
+									\
+      char expected[VFP_STACK_REQ] = { 0 };				\
+      for (int i = 0; i < 16; ++i)					\
+	expected[i * 8 + DISP] = i + 1;					\
+									\
+      if (memcmp (vfp, expected, VFP_STACK_REQ) != 0)			\
+        abort ();							\
+    }									\
+  if (hwcap & HWCAP_ARM_VFPD32)						\
+    {									\
+      CHECK_VFP_D32							\
+    }
+
+#endif /* __SOFTFP__ */
+
+#include_next <tst-gnu2-tls2.h>