sparc: Move sigreturn stub to assembly

Message ID 20200305192203.30217-1-adhemerval.zanella@linaro.org
State Accepted
Commit b33e946fbb1659d2c5937c4dd756a7c49a132dff
Headers show
Series
  • sparc: Move sigreturn stub to assembly
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Commit Message

Adhemerval Zanella March 5, 2020, 7:22 p.m.
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
---
 sysdeps/unix/sysv/linux/sparc/Makefile        |  8 +++--
 .../unix/sysv/linux/sparc/sparc32/sigaction.c | 26 ++---------------
 .../sysv/linux/sparc/sparc32/sigreturn_stub.S | 29 +++++++++++++++++++
 .../unix/sysv/linux/sparc/sparc64/sigaction.c | 14 ++-------
 .../sysv/linux/sparc/sparc64/sigreturn_stub.S | 24 +++++++++++++++
 5 files changed, 63 insertions(+), 38 deletions(-)
 create mode 100644 sysdeps/unix/sysv/linux/sparc/sparc32/sigreturn_stub.S
 create mode 100644 sysdeps/unix/sysv/linux/sparc/sparc64/sigreturn_stub.S

-- 
2.17.1

Comments

Zack Weinberg March 5, 2020, 9:34 p.m. | #1
On Thu, Mar 5, 2020 at 2:22 PM Adhemerval Zanella
<adhemerval.zanella@linaro.org> wrote:
>

> 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.


Could you add a comment explaining this to each of the new .S files?
"This function must not change the register window or the stack
pointer" would be enough, I think.  Maybe include the URL for [1].

zw
Adhemerval Zanella March 6, 2020, 4:19 p.m. | #2
On 05/03/2020 18:34, Zack Weinberg wrote:
> On Thu, Mar 5, 2020 at 2:22 PM Adhemerval Zanella

> <adhemerval.zanella@linaro.org> wrote:

>>

>> 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.

> 

> Could you add a comment explaining this to each of the new .S files?

> "This function must not change the register window or the stack

> pointer" would be enough, I think.  Maybe include the URL for [1].

> 

> zw

> 


Ack, I pushed with your suggestion plus the URL link.

Patch

diff --git a/sysdeps/unix/sysv/linux/sparc/Makefile b/sysdeps/unix/sysv/linux/sparc/Makefile
index b0d182a439..1475039677 100644
--- a/sysdeps/unix/sysv/linux/sparc/Makefile
+++ b/sysdeps/unix/sysv/linux/sparc/Makefile
@@ -11,8 +11,12 @@  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 6b2f664226..938aa7aa8c 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..347cef1349
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/sparc/sparc32/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>
+
+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 9c0dc2a630..4e26172321 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..6e0825fbf1
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/sparc/sparc64/sigreturn_stub.S
@@ -0,0 +1,24 @@ 
+/* 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>
+
+ENTRY (__rt_sigreturn_stub)
+	mov	__NR_rt_sigreturn, %g1
+	ta	0x6d
+END (__rt_sigreturn_stub)