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| author | Roland McGrath <roland@redhat.com> | 2008-06-23 20:41:12 -0700 |
|---|---|---|
| committer | Roland McGrath <roland@redhat.com> | 2008-07-23 17:43:36 -0700 |
| commit | 15e8f348db372dec21229fda5d52ae6ee7e64666 (patch) | |
| tree | 73afc044ef5b4e29a893e98afee2fe794938aeb3 /arch | |
| parent | 20b7997e8abdf338dcc27fb4f1333c4973a7f113 (diff) | |
| download | lwn-15e8f348db372dec21229fda5d52ae6ee7e64666.tar.gz lwn-15e8f348db372dec21229fda5d52ae6ee7e64666.zip | |
x86_64: remove bogus optimization in sysret_signal
This short-circuit path in sysret_signal looks wrong to me.
AFAICT, in practice the branch is never taken--and if it were,
it would go wrong. To wit, try loading a module whose init
function does set_thread_flag(TIF_IRET), and see insmod crash
(presumably with a wrong user stack pointer).
This is because the FIXUP_TOP_OF_STACK work hasn't been done yet
when we jump around the call to ptregscall_common and get to
int_with_check--where it expects the user RSP,SS,CS and EFLAGS to
have been stored by FIXUP_TOP_OF_STACK.
I don't think it's normally possible to get to sysret_signal with no
_TIF_DO_NOTIFY_MASK bits set anyway, so these two instructions are
already superfluous. If it ever did happen, it is harmless to call
do_notify_resume with nothing for it to do.
Signed-off-by: Roland McGrath <roland@redhat.com>
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/x86/kernel/entry_64.S | 6 |
1 files changed, 1 insertions, 5 deletions
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S index 8410e26f4183..a169225869cc 100644 --- a/arch/x86/kernel/entry_64.S +++ b/arch/x86/kernel/entry_64.S @@ -402,16 +402,12 @@ sysret_careful: sysret_signal: TRACE_IRQS_ON ENABLE_INTERRUPTS(CLBR_NONE) - testl $_TIF_DO_NOTIFY_MASK,%edx - jz 1f - - /* Really a signal */ /* edx: work flags (arg3) */ leaq do_notify_resume(%rip),%rax leaq -ARGOFFSET(%rsp),%rdi # &pt_regs -> arg1 xorl %esi,%esi # oldset -> arg2 call ptregscall_common -1: movl $_TIF_WORK_MASK,%edi + movl $_TIF_WORK_MASK,%edi /* Use IRET because user could have changed frame. This works because ptregscall_common has called FIXUP_TOP_OF_STACK. */ DISABLE_INTERRUPTS(CLBR_NONE) |