From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 2514 invoked by alias); 24 Sep 2019 13:16:26 -0000 Mailing-List: contact gdb-patches-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-patches-owner@sourceware.org Received: (qmail 127211 invoked by uid 89); 24 Sep 2019 13:16:21 -0000 Authentication-Results: sourceware.org; auth=none X-Spam-SWARE-Status: No, score=-25.6 required=5.0 tests=AWL,BAYES_00,GIT_PATCH_0,GIT_PATCH_1,GIT_PATCH_2,GIT_PATCH_3,SPF_PASS autolearn=ham version=3.3.1 spammy=iov, explains X-HELO: mx1.suse.de Received: from mx2.suse.de (HELO mx1.suse.de) (195.135.220.15) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with ESMTP; Tue, 24 Sep 2019 13:16:18 +0000 Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id E34B4AD79 for ; Tue, 24 Sep 2019 13:16:15 +0000 (UTC) Date: Tue, 24 Sep 2019 13:16:00 -0000 From: Tom de Vries To: gdb-patches@sourceware.org Subject: [PATCH][gdb/tdep] Handle mxcsr kernel bug on Intel Skylake CPUs Message-ID: <20190924131612.GA24708@delia> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.10.1 (2018-07-13) X-IsSubscribed: yes X-SW-Source: 2019-09/txt/msg00462.txt.bz2 Hi, On my openSUSE Leap 15.1 x86_64 Skylake system with the default (4.12) kernel, I run into: ... FAIL: gdb.base/gcore.exp: corefile restored all registers ... The problem is that there's a difference in the mxcsr register value before and after the gcore command: ... - mxcsr 0x0 [ ] + mxcsr 0x400440 [ DAZ OM ] ... This can be traced back to amd64_linux_nat_target::fetch_registers, where xstateregs is partially initialized by the ptrace call: ... char xstateregs[X86_XSTATE_MAX_SIZE]; struct iovec iov; amd64_collect_xsave (regcache, -1, xstateregs, 0); iov.iov_base = xstateregs; iov.iov_len = sizeof (xstateregs); if (ptrace (PTRACE_GETREGSET, tid, (unsigned int) NT_X86_XSTATE, (long) &iov) < 0) perror_with_name (_("Couldn't get extended state status")); amd64_supply_xsave (regcache, -1, xstateregs); ... after which amd64_supply_xsave is called. The amd64_supply_xsave call is supposed to only use initialized parts of xstateregs, but due to a kernel bug on intel skylake (fixed from 4.14 onwards by commit 0852b374173b "x86/fpu: Add FPU state copying quirk to handle XRSTOR failure on Intel Skylake CPUs") it can happen that the mxcsr part of xstateregs is not initialized, while amd64_supply_xsave expects it to be initialized, which explains the FAIL mentioned above. Fix the undetermined behaviour by initializing xstateregs before calling ptrace, which makes sure we get a 0x0 for mxcsr when this kernel bug occurs, and which also happens to fix the FAIL. Furthermore, add an xfail for this FAIL which triggers the same kernel bug: ... FAIL: gdb.arch/amd64-init-x87-values.exp: check_setting_mxcsr_before_enable: \ check new value of MXCSR is still in place ... Both FAILs pass when using a 5.3 kernel instead on the system mentioned above. Tested on x86_64-linux. OK for trunk? Thanks, - Tom [gdb/tdep] Handle mxcsr kernel bug on Intel Skylake CPUs gdb/ChangeLog: 2019-09-24 Tom de Vries PR gdb/23815 * amd64-linux-nat.c (amd64_linux_nat_target::fetch_registers): Initialize xstateregs before ptrace PTRACE_GETREGSET call. gdb/testsuite/ChangeLog: 2019-09-24 Tom de Vries PR gdb/24598 * gdb.arch/amd64-init-x87-values.exp: Add xfail. --- gdb/amd64-linux-nat.c | 1 + gdb/testsuite/gdb.arch/amd64-init-x87-values.exp | 19 +++++++++++++++++-- 2 files changed, 18 insertions(+), 2 deletions(-) diff --git a/gdb/amd64-linux-nat.c b/gdb/amd64-linux-nat.c index 4f1c98a0d1..984b3d7c0f 100644 --- a/gdb/amd64-linux-nat.c +++ b/gdb/amd64-linux-nat.c @@ -238,6 +238,7 @@ amd64_linux_nat_target::fetch_registers (struct regcache *regcache, int regnum) char xstateregs[X86_XSTATE_MAX_SIZE]; struct iovec iov; + memset (xstateregs, 0, sizeof (xstateregs)); iov.iov_base = xstateregs; iov.iov_len = sizeof (xstateregs); if (ptrace (PTRACE_GETREGSET, tid, diff --git a/gdb/testsuite/gdb.arch/amd64-init-x87-values.exp b/gdb/testsuite/gdb.arch/amd64-init-x87-values.exp index cdf92dcd37..5fd18dbb79 100644 --- a/gdb/testsuite/gdb.arch/amd64-init-x87-values.exp +++ b/gdb/testsuite/gdb.arch/amd64-init-x87-values.exp @@ -116,7 +116,7 @@ proc_with_prefix check_x87_regs_around_init {} { # nop that does not enable any FP features). Finally check that the # mxcsr register still has the value we set. proc_with_prefix check_setting_mxcsr_before_enable {} { - global binfile + global binfile gdb_prompt clean_restart ${binfile} @@ -127,7 +127,22 @@ proc_with_prefix check_setting_mxcsr_before_enable {} { gdb_test_no_output "set \$mxcsr=0x9f80" "set a new value for MXCSR" gdb_test "stepi" "fwait" "step forward one instruction for mxcsr test" - gdb_test "p/x \$mxcsr" " = 0x9f80" "check new value of MXCSR is still in place" + + set test "check new value of MXCSR is still in place" + set pass_pattern " = 0x9f80" + # Pre-4.14 kernels have a bug (fixed by commit 0852b374173b "x86/fpu: + # Add FPU state copying quirk to handle XRSTOR failure on Intel Skylake + # CPUs") that causes mxcsr not to be copied, in which case we get 0 instead of + # the just saved value. + set xfail_pattern " = 0x0" + gdb_test_multiple "p/x \$mxcsr" $test { + -re "\[\r\n\]*(?:$pass_pattern)\[\r\n\]+$gdb_prompt $" { + pass $test + } + -re "\[\r\n\]*(?:$xfail_pattern)\[\r\n\]+$gdb_prompt $" { + xfail $test + } + } } # Start the test file, all FP features will be disabled. Set new