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authorIngo Molnar <mingo@elte.hu>2008-11-27 14:41:21 +0100
committerIngo Molnar <mingo@elte.hu>2008-11-28 15:01:46 +0100
commit5b3eec0c80038c8739ccd465b897a35c0dff1cc4 (patch)
tree52a4625c34af62dc41233ecdf21e2d5262683e8f /arch/x86/kernel/entry_64.S
parent3bdae4f46445ea7cc9ee031d7ff106fdc6228669 (diff)
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/entry_64.S')
-rw-r--r--arch/x86/kernel/entry_64.S31
1 files changed, 16 insertions, 15 deletions
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index e41734a537b..3194636a429 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)