From 3d4352200e3e98a6d8855e6f3a39b6d33d84e36b Mon Sep 17 00:00:00 2001 From: Tom de Vries Date: Tue, 24 Sep 2019 23:38:49 +0200 Subject: [PATCH] [gdb/tdep] Handle mxcsr kernel bug on Intel Skylake CPUs 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. 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/ChangeLog | 6 ++++++ gdb/amd64-linux-nat.c | 6 ++++++ gdb/testsuite/ChangeLog | 5 +++++ .../gdb.arch/amd64-init-x87-values.exp | 19 +++++++++++++++++-- 4 files changed, 34 insertions(+), 2 deletions(-) diff --git a/gdb/ChangeLog b/gdb/ChangeLog index 77aab764924..ee53e9c00a5 100644 --- a/gdb/ChangeLog +++ b/gdb/ChangeLog @@ -1,3 +1,9 @@ +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. + 2019-09-23 Dimitar Dimitrov * NEWS: Mention new simulator port for PRU. diff --git a/gdb/amd64-linux-nat.c b/gdb/amd64-linux-nat.c index 4f1c98a0d1e..d0328b677d5 100644 --- a/gdb/amd64-linux-nat.c +++ b/gdb/amd64-linux-nat.c @@ -238,6 +238,12 @@ amd64_linux_nat_target::fetch_registers (struct regcache *regcache, int regnum) char xstateregs[X86_XSTATE_MAX_SIZE]; struct iovec iov; + /* 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 sometimes causes the mxcsr location in + xstateregs not to be copied by PTRACE_GETREGSET. Make sure that + the location is at least initialized with a defined value. */ + memset (xstateregs, 0, sizeof (xstateregs)); iov.iov_base = xstateregs; iov.iov_len = sizeof (xstateregs); if (ptrace (PTRACE_GETREGSET, tid, diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog index 37e323f747c..706c5da420a 100644 --- a/gdb/testsuite/ChangeLog +++ b/gdb/testsuite/ChangeLog @@ -1,3 +1,8 @@ +2019-09-24 Tom de Vries + + PR gdb/24598 + * gdb.arch/amd64-init-x87-values.exp: Add xfail. + 2019-09-22 Tom de Vries * gdb.base/restore.exp: Allow register variables to be optimized out at diff --git a/gdb/testsuite/gdb.arch/amd64-init-x87-values.exp b/gdb/testsuite/gdb.arch/amd64-init-x87-values.exp index cdf92dcd377..5fd18dbb794 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 -- 2.30.2