[glibc/release/2.30/master] sparc: Move sigreturn stub to assembly

Adhemerval Zanella azanella@sourceware.org
Tue Mar 24 11:51:05 GMT 2020


https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=b3778c01b74fe4d42fad9841576ecca0c1698556

commit b3778c01b74fe4d42fad9841576ecca0c1698556
Author: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Date:   Thu Mar 5 13:38:24 2020 -0300

    sparc: Move sigreturn stub to assembly
    
    It seems that some gcc versions might generates a stack frame for the
    sigreturn stub requires on sparc signal handling.  For instance:
    
      $ cat test.c
      #define _GNU_SOURCE
      #include <sys/syscall.h>
    
      __attribute__ ((__optimize__ ("-fno-stack-protector")))
      void
      __sigreturn_stub (void)
      {
        __asm__ ("mov %0, %%g1\n\t"
                "ta  0x10\n\t"
                : /* no outputs */
                : "i" (SYS_rt_sigreturn));
      }
      $ gcc -v
      [...]
      gcc version 9.2.1 20200224 (Debian 9.2.1-30)
      $ gcc -O2 -m64 test.c -S -o -
      [...]
        __sigreturn_stub:
              save    %sp, -176, %sp
      #APP
      ! 9 "t.c" 1
              mov 101, %g1
              ta  0x10
    
      ! 0 "" 2
      #NO_APP
              .size   __sigreturn_stub, .-__sigreturn_stub
    
    As indicated by kernel developers [1], the sigreturn stub can not change
    the register window or the stack pointer since the kernel has setup the
    restore frame at a precise location relative to the stack pointer when
    the stub is invoked.
    
    I tried to play with some compiler flags and even with _Noreturn and
    __builtin_unreachable after the asm does not help (and Sparc does not
    support naked functions).
    
    To avoid similar issues, as the stack-protector support also have
    stumbled, this patch moves the implementation of the sigreturn stubs to
    assembly.
    
    Checked on sparcv9-linux-gnu and sparc64-linux-gnu with gcc 9.2.1
    and gcc 7.5.0.
    
    [1] https://lkml.org/lkml/2016/5/27/465
    
    (cherry picked from commit b33e946fbb1659d2c5937c4dd756a7c49a132dff)

Diff:
---
 sysdeps/unix/sysv/linux/sparc/Makefile             |  8 +++--
 sysdeps/unix/sysv/linux/sparc/sparc32/sigaction.c  | 26 ++---------------
 .../unix/sysv/linux/sparc/sparc32/sigreturn_stub.S | 34 ++++++++++++++++++++++
 sysdeps/unix/sysv/linux/sparc/sparc64/sigaction.c  | 14 ++-------
 .../unix/sysv/linux/sparc/sparc64/sigreturn_stub.S | 29 ++++++++++++++++++
 5 files changed, 73 insertions(+), 38 deletions(-)

diff --git a/sysdeps/unix/sysv/linux/sparc/Makefile b/sysdeps/unix/sysv/linux/sparc/Makefile
index fb3ee5b8a1..7b91ff1824 100644
--- a/sysdeps/unix/sysv/linux/sparc/Makefile
+++ b/sysdeps/unix/sysv/linux/sparc/Makefile
@@ -15,8 +15,12 @@ ifeq ($(subdir),sysvipc)
 sysdep_routines += getshmlba
 endif
 
+ifeq ($(subdir),signal)
+sysdep_routines += sigreturn_stub
+endif
+
 ifeq ($(subdir),nptl)
 # pull in __syscall_error routine
-libpthread-routines += sysdep
-libpthread-shared-only-routines += sysdep
+libpthread-routines += sysdep sigreturn_stub
+libpthread-shared-only-routines += sysdep sigreturn_stub
 endif
diff --git a/sysdeps/unix/sysv/linux/sparc/sparc32/sigaction.c b/sysdeps/unix/sysv/linux/sparc/sparc32/sigaction.c
index de7ef6f151..f36e924af4 100644
--- a/sysdeps/unix/sysv/linux/sparc/sparc32/sigaction.c
+++ b/sysdeps/unix/sysv/linux/sparc/sparc32/sigaction.c
@@ -24,8 +24,8 @@
 #include <kernel_sigaction.h>
 #include <sysdep.h>
 
-static void __rt_sigreturn_stub (void);
-static void __sigreturn_stub (void);
+void __rt_sigreturn_stub (void);
+void __sigreturn_stub (void);
 
 #define STUB(act, sigsetsize) \
   (act) ? ((unsigned long)((act->sa_flags & SA_SIGINFO)	\
@@ -35,25 +35,3 @@ static void __sigreturn_stub (void);
   (sigsetsize)
 
 #include <sysdeps/unix/sysv/linux/sigaction.c>
-
-static
-inhibit_stack_protector
-void
-__rt_sigreturn_stub (void)
-{
-  __asm__ ("mov %0, %%g1\n\t"
-	   "ta	0x10\n\t"
-	   : /* no outputs */
-	   : "i" (__NR_rt_sigreturn));
-}
-
-static
-inhibit_stack_protector
-void
-__sigreturn_stub (void)
-{
-  __asm__ ("mov %0, %%g1\n\t"
-	   "ta	0x10\n\t"
-	   : /* no outputs */
-	   : "i" (__NR_sigreturn));
-}
diff --git a/sysdeps/unix/sysv/linux/sparc/sparc32/sigreturn_stub.S b/sysdeps/unix/sysv/linux/sparc/sparc32/sigreturn_stub.S
new file mode 100644
index 0000000000..727cc94737
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/sparc/sparc32/sigreturn_stub.S
@@ -0,0 +1,34 @@
+/* Sigreturn stub function used on sa_restore field.
+   Copyright (C) 2020 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>
+
+/* These functions must not change the register window or the stack
+   pointer [1].
+
+   [1] https://lkml.org/lkml/2016/5/27/465  */
+
+ENTRY (__rt_sigreturn_stub)
+	mov	__NR_rt_sigreturn, %g1
+	ta	0x10
+END (__rt_sigreturn_stub)
+
+ENTRY (__sigreturn_stub)
+	mov	__NR_sigreturn, %g1
+	ta	0x10
+END (__sigreturn_stub)
diff --git a/sysdeps/unix/sysv/linux/sparc/sparc64/sigaction.c b/sysdeps/unix/sysv/linux/sparc/sparc64/sigaction.c
index 3b8be43c07..4772ec2553 100644
--- a/sysdeps/unix/sysv/linux/sparc/sparc64/sigaction.c
+++ b/sysdeps/unix/sysv/linux/sparc/sparc64/sigaction.c
@@ -22,21 +22,11 @@
 #include <syscall.h>
 #include <sysdep.h>
 
-static void __rt_sigreturn_stub (void);
+/* Defined on sigreturn_stub.S.  */
+void __rt_sigreturn_stub (void);
 
 #define STUB(act, sigsetsize) \
   (((unsigned long) &__rt_sigreturn_stub) - 8),	\
   (sigsetsize)
 
 #include <sysdeps/unix/sysv/linux/sigaction.c>
-
-static
-inhibit_stack_protector
-void
-__rt_sigreturn_stub (void)
-{
-  __asm__ ("mov %0, %%g1\n\t"
-	   "ta	0x6d\n\t"
-	   : /* no outputs */
-	   : "i" (__NR_rt_sigreturn));
-}
diff --git a/sysdeps/unix/sysv/linux/sparc/sparc64/sigreturn_stub.S b/sysdeps/unix/sysv/linux/sparc/sparc64/sigreturn_stub.S
new file mode 100644
index 0000000000..add4766831
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/sparc/sparc64/sigreturn_stub.S
@@ -0,0 +1,29 @@
+/* Sigreturn stub function used on sa_restore field.
+   Copyright (C) 2020 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 function must not change the register window or the stack
+   pointer [1].
+
+   [1] https://lkml.org/lkml/2016/5/27/465  */
+
+ENTRY (__rt_sigreturn_stub)
+	mov	__NR_rt_sigreturn, %g1
+	ta	0x6d
+END (__rt_sigreturn_stub)


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