[glibc] Implement _Unwind_Resume in libc on top of <unwind-link.h>

[glibc] Implement _Unwind_Resume in libc on top of <unwind-link.h>

[Florian Weimer]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=6b7efa3d8703cfd020281706f8110bc4a41b1525

commit 6b7efa3d8703cfd020281706f8110bc4a41b1525
Author: Florian Weimer <fweimer@redhat.com>
Date:   Mon Mar 1 15:56:36 2021 +0100

    Implement _Unwind_Resume in libc on top of <unwind-link.h>
    
    Temporarily move the arm _Unwind_Resume implementation to the file
    used by libpthread.  It will be ported to <unwind-link.h> along with
    the rest of nptl.
    
    Reviewed-by: Carlos O'Donell <carlos@redhat.com>

Diff:
---
 sysdeps/arm/arm-unwind-resume.S    | 26 +++++++++---------
 sysdeps/arm/pt-arm-unwind-resume.S | 48 +++++++++++++++++++++++++++++++--
 sysdeps/arm/unwind-arch.h          |  4 +++
 sysdeps/arm/unwind-resume.c        | 25 +++++++++++++++++
 sysdeps/generic/unwind-resume.c    | 55 +++++++-------------------------------
 5 files changed, 97 insertions(+), 61 deletions(-)

diff --git a/sysdeps/arm/arm-unwind-resume.S b/sysdeps/arm/arm-unwind-resume.S
index 22525f4db0..92c171fe0f 100644
--- a/sysdeps/arm/arm-unwind-resume.S
+++ b/sysdeps/arm/arm-unwind-resume.S
@@ -18,29 +18,29 @@
 
 #include <sysdep.h>
 
-/* This is just implementing exactly what the C version does.
+/* This is equivalent to the following C implementation:
+
+   void
+   _Unwind_Resume (struct _Unwind_Exception *exc)
+   {
+     __unwind_link_get_resume () (exc);
+   }
+
    We do it in assembly just to ensure that we get an unmolested tail
    call to the libgcc function, which is necessary for the ARM unwinder.  */
 
 ENTRY (_Unwind_Resume)
-	LDR_HIDDEN (ip, ip, __libgcc_s_resume, 0)
-	cmp	ip, #0
-	beq	1f
-0:	PTR_DEMANGLE (ip, ip, r2, r3)
-	bx	ip
-
 	/* We need to save and restore LR (for our own return address)
 	   and R0 (for the argument to _Unwind_Resume) around the call.  */
-1:	push	{r0, lr}
+	push	{r0, lr}
 	cfi_adjust_cfa_offset (8)
 	cfi_rel_offset (r0, 0)
 	cfi_rel_offset (lr, 4)
-	bl	__libgcc_s_init
+	bl	__unwind_link_get_resume
+	mov	r3, r0
 	pop	{r0, lr}
 	cfi_adjust_cfa_offset (-8)
-	cfi_restore (r0)
+	cfi_restore (r4)
 	cfi_restore (lr)
-
-	LDR_HIDDEN (ip, ip, __libgcc_s_resume, 0)
-	b	0b
+	bx	r3
 END (_Unwind_Resume)
diff --git a/sysdeps/arm/pt-arm-unwind-resume.S b/sysdeps/arm/pt-arm-unwind-resume.S
index 7cb555c02b..d579848696 100644
--- a/sysdeps/arm/pt-arm-unwind-resume.S
+++ b/sysdeps/arm/pt-arm-unwind-resume.S
@@ -1,2 +1,46 @@
-#define __libgcc_s_init	pthread_cancel_init
-#include <arm-unwind-resume.S>
+/* _Unwind_Resume wrapper for ARM EABI.
+   Copyright (C) 2015-2021 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 <sysdep.h>
+
+/* This is just implementing exactly what the C version does.
+   We do it in assembly just to ensure that we get an unmolested tail
+   call to the libgcc function, which is necessary for the ARM unwinder.  */
+
+ENTRY (_Unwind_Resume)
+	LDR_HIDDEN (ip, ip, __libgcc_s_resume, 0)
+	cmp	ip, #0
+	beq	1f
+0:	PTR_DEMANGLE (ip, ip, r2, r3)
+	bx	ip
+
+	/* We need to save and restore LR (for our own return address)
+	   and R0 (for the argument to _Unwind_Resume) around the call.  */
+1:	push	{r0, lr}
+	cfi_adjust_cfa_offset (8)
+	cfi_rel_offset (r0, 0)
+	cfi_rel_offset (lr, 4)
+	bl	pthread_cancel_init
+	pop	{r0, lr}
+	cfi_adjust_cfa_offset (-8)
+	cfi_restore (r0)
+	cfi_restore (lr)
+
+	LDR_HIDDEN (ip, ip, __libgcc_s_resume, 0)
+	b	0b
+END (_Unwind_Resume)
diff --git a/sysdeps/arm/unwind-arch.h b/sysdeps/arm/unwind-arch.h
index fcf889b3c7..62f643b221 100644
--- a/sysdeps/arm/unwind-arch.h
+++ b/sysdeps/arm/unwind-arch.h
@@ -32,4 +32,8 @@
   assert (local.ptr__Unwind_VRS_Get != NULL);                 \
   PTR_MANGLE (local.ptr__Unwind_VRS_Get);
 
+/* This is used by the _Unwind_Resume assembler implementation to
+   obtain the address to jump to.  */
+void *__unwind_link_get_resume (void) attribute_hidden;
+
 #endif /* _ARCH_UNWIND_LINK_H */
diff --git a/sysdeps/arm/unwind-resume.c b/sysdeps/arm/unwind-resume.c
new file mode 100644
index 0000000000..169d5c30e6
--- /dev/null
+++ b/sysdeps/arm/unwind-resume.c
@@ -0,0 +1,25 @@
+/* Unwinder function forwarders for libc.  Arm version.
+   Copyright (C) 2021 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; see the file COPYING.LIB.  If
+   not, see <https://www.gnu.org/licenses/>.  */
+
+#include <sysdeps/generic/unwind-resume.c>
+
+void *
+__unwind_link_get_resume (void)
+{
+  return UNWIND_LINK_PTR (link (), _Unwind_Resume);
+}
diff --git a/sysdeps/generic/unwind-resume.c b/sysdeps/generic/unwind-resume.c
index 09533d6992..9e63762bf1 100644
--- a/sysdeps/generic/unwind-resume.c
+++ b/sysdeps/generic/unwind-resume.c
@@ -16,68 +16,31 @@
    License along with the GNU C Library; see the file COPYING.LIB.  If
    not, see <https://www.gnu.org/licenses/>.  */
 
-#include <dlfcn.h>
 #include <stdio.h>
-#include <unwind.h>
 #include <gnu/lib-names.h>
+#include <unwind-link.h>
 #include <sysdep.h>
 #include <unwind-resume.h>
 
-
-void (*__libgcc_s_resume) (struct _Unwind_Exception *exc)
-  attribute_hidden __attribute__ ((noreturn));
-
-static _Unwind_Reason_Code (*libgcc_s_personality) PERSONALITY_PROTO;
-
-void attribute_hidden __attribute__ ((cold))
-__libgcc_s_init (void)
+static struct unwind_link *
+link (void)
 {
-  void *resume, *personality;
-  void *handle;
-
-  /* See include/dlfcn.h. Use of __libc_dlopen requires RTLD_NOW.  */
-  handle = __libc_dlopen (LIBGCC_S_SO);
-
-  if (handle == NULL
-      || (resume = __libc_dlsym (handle, "_Unwind_Resume")) == NULL
-      || (personality = __libc_dlsym (handle, "__gcc_personality_v0")) == NULL)
-    __libc_fatal (LIBGCC_S_SO
-                  " must be installed for unwinding to work\n");
-
-#ifdef PTR_MANGLE
-  PTR_MANGLE (resume);
-#endif
-  __libgcc_s_resume = resume;
-#ifdef PTR_MANGLE
-  PTR_MANGLE (personality);
-#endif
-  libgcc_s_personality = personality;
+  struct unwind_link *unwind_link = __libc_unwind_link_get ();
+  if (unwind_link == NULL)
+    __libc_fatal (LIBGCC_S_SO " must be installed for unwinding to work\n");
+  return unwind_link;
 }
 
 #if !HAVE_ARCH_UNWIND_RESUME
 void
 _Unwind_Resume (struct _Unwind_Exception *exc)
 {
-  if (__glibc_unlikely (__libgcc_s_resume == NULL))
-    __libgcc_s_init ();
-
-  __typeof (__libgcc_s_resume) resume = __libgcc_s_resume;
-#ifdef PTR_DEMANGLE
-  PTR_DEMANGLE (resume);
-#endif
-  (*resume) (exc);
+  UNWIND_LINK_PTR (link (), _Unwind_Resume) (exc);
 }
 #endif
 
 _Unwind_Reason_Code
 __gcc_personality_v0 PERSONALITY_PROTO
 {
-  if (__glibc_unlikely (libgcc_s_personality == NULL))
-    __libgcc_s_init ();
-
-  __typeof (libgcc_s_personality) personality = libgcc_s_personality;
-#ifdef PTR_DEMANGLE
-  PTR_DEMANGLE (personality);
-#endif
-  return (*personality) PERSONALITY_ARGS;
+  return UNWIND_LINK_PTR (link (), personality) PERSONALITY_ARGS;
 }