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Fill FPU init state if it's not provided by kernel.

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Apparently Skylake uses init-optimization when saving FPU state, and ptrace()
returns XSTATE_BV[0] = 0 meaning FPU was not used by a task (in init state).
Since CRIU restore uses sigreturn to restore registers, FPU state is always
restored. Fill the state with default values on dump to make restore happy.

Signed-off-by: Michał Mirosław <emmir@google.com>
This commit is contained in:
Michał Mirosław 2021-10-13 06:32:43 +02:00 • committed by Andrei Vagin
parent 93ad8d40de
commit 4c1409b8f6
1 changed files with 19 additions and 8 deletions
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27
compel/arch/x86/src/lib/infect.c
View file

@ -220,6 +220,16 @@ int sigreturn_prep_fpu_frame_plain(struct rt_sigframe *sigframe, struct rt_sigfr
#define get_signed_user_reg(pregs, name) \
((user_regs_native(pregs)) ? (int64_t)((pregs)->native.name) : (int32_t)((pregs)->compat.name))
static int get_task_fpregs(pid_t pid, user_fpregs_struct_t *xsave)
{
if (ptrace(PTRACE_GETFPREGS, pid, NULL, xsave)) {
pr_perror("Can't obtain FPU registers for %d", pid);
return -1;
}
return 0;
}
static int get_task_xsave(pid_t pid, user_fpregs_struct_t *xsave)
{
struct iovec iov;
@ -232,14 +242,15 @@ static int get_task_xsave(pid_t pid, user_fpregs_struct_t *xsave)
return -1;
}
return 0;
}
static int get_task_fpregs(pid_t pid, user_fpregs_struct_t *xsave)
{
if (ptrace(PTRACE_GETFPREGS, pid, NULL, xsave)) {
pr_perror("Can't obtain FPU registers for %d", pid);
return -1;
if ((xsave->xsave_hdr.xstate_bv & 3) != 3) {
// Due to init-optimisation [1] x87 FPU or SSE state may not be filled in.
// Since those are restored unconditionally, make sure the init values are
// filled by retrying with old PTRACE_GETFPREGS.
//
// [1] Intel® 64 and IA-32 Architectures Software Developer's
// Manual Volume 1: Basic Architecture
// Section 13.6: Processor tracking of XSAVE-managed state
return get_task_fpregs(pid, xsave);
}
return 0;