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| author | Ingo Molnar <mingo@elte.hu> | 2008-11-27 14:41:21 +0100 |
|---|---|---|
| committer | Ingo Molnar <mingo@elte.hu> | 2008-11-28 15:01:46 +0100 |
| commit | 5b3eec0c80038c8739ccd465b897a35c0dff1cc4 (patch) | |
| tree | 52a4625c34af62dc41233ecdf21e2d5262683e8f /arch/x86/kernel | |
| parent | 3bdae4f46445ea7cc9ee031d7ff106fdc6228669 (diff) | |
| download | blackbird-obmc-linux-5b3eec0c80038c8739ccd465b897a35c0dff1cc4.tar.gz blackbird-obmc-linux-5b3eec0c80038c8739ccd465b897a35c0dff1cc4.zip | |
x86: ret_from_fork - get rid of jump back
Impact: remove dead code
If we take a closer look at the rff_trace/rff_action ret_from_fork code,
we have to realize that it does all the wrong things: for example it
checks the TIF flag - while later on jumping back to the ret-from-syscall
path - duplicating the check needlessly.
But checking for _TIF_SYSCALL_TRACE is completely unnecessary here because
we clear that flag for every freshly forked task. So the whole "tracing"
code here, for which there is a out of line jump optimization that makes
it even harder to read, is in reality completely dead code ...
Reported-by: Cyrill Gorcunov <gorcunov@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Tested-by: Cyrill Gorcunov <gorcunov@gmail.com>
Diffstat (limited to 'arch/x86/kernel')
| -rw-r--r-- | arch/x86/kernel/entry_64.S | 31 |
1 files changed, 16 insertions, 15 deletions
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S index e41734a537bd..3194636a4293 100644 --- a/arch/x86/kernel/entry_64.S +++ b/arch/x86/kernel/entry_64.S @@ -361,34 +361,35 @@ ENTRY(save_paranoid) END(save_paranoid) /* - * A newly forked process directly context switches into this. + * A newly forked process directly context switches into this address. + * + * rdi: prev task we switched from */ -/* rdi: prev */ ENTRY(ret_from_fork) DEFAULT_FRAME + push kernel_eflags(%rip) CFI_ADJUST_CFA_OFFSET 8 - popf # reset kernel eflags + popf # reset kernel eflags CFI_ADJUST_CFA_OFFSET -8 - call schedule_tail + + call schedule_tail # rdi: 'prev' task parameter + GET_THREAD_INFO(%rcx) - testl $(_TIF_SYSCALL_TRACE|_TIF_SYSCALL_AUDIT),TI_flags(%rcx) + CFI_REMEMBER_STATE - jnz rff_trace -rff_action: RESTORE_REST - testl $3,CS-ARGOFFSET(%rsp) # from kernel_thread? + + testl $3, CS-ARGOFFSET(%rsp) # from kernel_thread? je int_ret_from_sys_call - testl $_TIF_IA32,TI_flags(%rcx) + + testl $_TIF_IA32, TI_flags(%rcx) # 32-bit compat task needs IRET jnz int_ret_from_sys_call + RESTORE_TOP_OF_STACK %rdi, -ARGOFFSET - jmp ret_from_sys_call + jmp ret_from_sys_call # go to the SYSRET fastpath + CFI_RESTORE_STATE -rff_trace: - movq %rsp,%rdi - call syscall_trace_leave - GET_THREAD_INFO(%rcx) - jmp rff_action CFI_ENDPROC END(ret_from_fork) |
