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Re: [PATCH] power: Fix VSCR position on ucontext

I am sending patch v4 attached in this email with the fixes proposed here. Thank you all for the review on this patch.


Em 10-12-2018 16:38, Tulio Magno Quites Machado Filho escreveu:
"Gabriel F. T. Gomes" <> writes:

On Fri, 07 Dec 2018, Gabriel F. T. Gomes wrote:

On Fri, 07 Dec 2018, Rogerio Alves wrote:

+/* This test is supported only on POWER 5 or higher.  */
+                           PPC_FEATURE_ARCH_2_05 | PPC_FEATURE_ARCH_2_06 | \
+                           PPC_FEATURE2_ARCH_2_07)

Is this actually needed?  Glibc has code to fill all the bits for older
architectures in sysdeps/powerpc/hwcapinfo.c [1].  So, as far as I can
see, you only need to test for AT_HWCAP & PPC_FEATURE_POWER5.


Hrm, that's only true for the hwcap info that is copied into the TCB, not
when accessing it with getauxval, so my comment is wrong (as Rogerio
kindly pointed out to me in a private message...  thanks).

So, nevermind this comment.

On the other hand, on powerpc64 builds configured with --with-cpu set to
power4, power5, and power6, (but not to power8 or power7), I got the
following error message:

../sysdeps/powerpc/powerpc64/tst-ucontext-ppc64-vscr.c: In function ‘do_test’:
../sysdeps/powerpc/powerpc64/tst-ucontext-ppc64-vscr.c:51:3: error: inconsistent operand constraints in an ‘asm’
    asm volatile ("vspltisb %0,0\n"

I guess we didn't get this error message before, because of the
`#ifdef ARCH_PWR8' statement.  So, unless you know a better way to fix
this, you should reintroduce the `#ifdef' statement (now, you could use

You can use:

     .machine push;
     .machine "power7";
     .machine pop

It should be safe to use with the current minimum required Binutils i.e.
support for POWER7 was already available in GNU Binutils 2.25 (even P8 was

Done. Using your suggestion fixed the issue thanks
>From 2fe5a2b78f6818000ef59084098b6d17d8becd0a Mon Sep 17 00:00:00 2001
From: Rogerio Alves <>
Date: Mon, 5 Nov 2018 10:18:38 -0600
Subject: [PATCH v4] powerpc: Fix VSCR position in ucontext.

This patch fix VSCR position on ucontext. VSCR was read in the wrong
position on ucontext structure because it was ignoring the machine

2018-11-05  Rogerio A. Cardoso  <>

	* sysdeps/unix/sysv/linux/powerpc/sys/ucontext.h
    (struct _libc_vscr, vscr_t): Added ifdef to fix read of VSCR.
	* sysdeps/powerpc/powerpc64/Makefile: Add tst-ucontext-ppc64-vscr.c
    to test list.
	* sysdeps/powerpc/powerpc64/tst-ucontext-ppc64-vscr.c: New test file.
 Patch v4: fixed as per Tulio review. Using machine push/pop to generate
 power7 instructions.

 Patch v3: fixed as per Florian and Gabriel review. Using getauxval to get
 if (runtime) the test is supported instead using ifdef. Changed
 vpkudus por vpkuwus since it's supported by POWER 5 or higher.

 Patch v2: fixed as per Gabriel and Segher review. Fix formating and changelog
 Change the assembly inline to a better version. Changed ifdef to POWER8.

 sysdeps/powerpc/powerpc64/Makefile                 |  5 ++
 .../powerpc/powerpc64/tst-ucontext-ppc64-vscr.c    | 85 ++++++++++++++++++++++
 sysdeps/unix/sysv/linux/powerpc/sys/ucontext.h     |  5 ++
 3 files changed, 95 insertions(+)
 create mode 100644 sysdeps/powerpc/powerpc64/tst-ucontext-ppc64-vscr.c

diff --git a/sysdeps/powerpc/powerpc64/Makefile b/sysdeps/powerpc/powerpc64/Makefile
index a0bd0c9..6e88df1 100644
--- a/sysdeps/powerpc/powerpc64/Makefile
+++ b/sysdeps/powerpc/powerpc64/Makefile
@@ -59,3 +59,8 @@ $(objpfx)tst-setjmp-bug21895-static.out: $(objpfx)
 tst-setjmp-bug21895-static-ENV = \
+ifeq ($(subdir),stdlib)
+CFLAGS-tst-ucontext-ppc64-vscr.c += -maltivec
+tests += tst-ucontext-ppc64-vscr
diff --git a/sysdeps/powerpc/powerpc64/tst-ucontext-ppc64-vscr.c b/sysdeps/powerpc/powerpc64/tst-ucontext-ppc64-vscr.c
new file mode 100644
index 0000000..02c06cb
--- /dev/null
+++ b/sysdeps/powerpc/powerpc64/tst-ucontext-ppc64-vscr.c
@@ -0,0 +1,85 @@
+/* Test if POWER vscr read by ucontext.
+   Copyright (C) 2018 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
+   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 <support/check.h>
+#include <sys/auxv.h>
+#include <ucontext.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <stdint.h>
+#include <altivec.h>
+#define SAT 0x1
+/* This test is supported only on POWER 5 or higher.  */
+                           PPC_FEATURE_ARCH_2_05 | PPC_FEATURE_ARCH_2_06 | \
+                           PPC_FEATURE2_ARCH_2_07)
+static int
+do_test (void)
+  if (!(getauxval(AT_HWCAP2) & PPC_CPU_SUPPORTED))
+    {
+      if (!(getauxval(AT_HWCAP) & PPC_CPU_SUPPORTED))
+      FAIL_UNSUPPORTED("This test is unsupported on POWER < 5\n");
+    }
+  uint32_t vscr[4] __attribute__ ((aligned (16)));
+  uint32_t* vscr_ptr = vscr;
+  uint32_t vscr_word;
+  ucontext_t ucp;
+  __vector __int128_t v0 = {0};
+  __vector __int128_t v1 = {0};
+  /* Set SAT bit in VSCR register.  */
+  asm volatile (".machine push;\n"
+                ".machine \"power7\";\n"
+                "vspltisb %0,0;\n"
+                "vspltisb %1,-1;\n"
+                "vpkuwus %0,%0,%1;\n"
+                "mfvscr %0;\n"
+                "stvx %0,0,%2;\n"
+                ".machine pop;"
+       : "=v" (v0), "=v" (v1)
+       : "r" (vscr_ptr)
+       : "memory"
+       );
+  vscr_word = vscr[0];
+  vscr_word = vscr[3];
+  if ((vscr_word & SAT) != SAT)
+    {
+      FAIL_EXIT1("FAIL: SAT bit is not set.\n");
+    }
+  if (getcontext (&ucp))
+    {
+      FAIL_EXIT1("FAIL: getcontext error\n");
+    }
+  if (ucp.uc_mcontext.v_regs->vscr.vscr_word != vscr_word)
+    {
+      FAIL_EXIT1("FAIL: ucontext vscr does not match with vscr\n");
+    }
+  return 0;
+#include <support/test-driver.c>
diff --git a/sysdeps/unix/sysv/linux/powerpc/sys/ucontext.h b/sysdeps/unix/sysv/linux/powerpc/sys/ucontext.h
index 1bb6e4c..49a92c5 100644
--- a/sysdeps/unix/sysv/linux/powerpc/sys/ucontext.h
+++ b/sysdeps/unix/sysv/linux/powerpc/sys/ucontext.h
@@ -98,8 +98,13 @@ typedef double fpregset_t[__NFPREG];
    a whole quadword speedup save/restore.  */
 typedef struct _libc_vscr
 	unsigned int __pad[3];
 	unsigned int __ctx(vscr_word);
+	unsigned int __ctx(vscr_word);
+	unsigned int __pad[3];
 } vscr_t;
 /* Container for Altivec/VMX registers and status.

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