[RFC 23/30] x86/entry/32: Open-code return tracking from fork and kthreads

From: Andy Lutomirski
Date: Tue Sep 01 2015 - 18:44:37 EST


syscall_exit is going away, and return tracing is just a function
call now, so open-code the two non-syscall 32-bit users.

While we're at it, update the big register layout comment.

Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
---
arch/x86/entry/entry_32.S | 18 +++++++++++++++---
1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index a08ded481aba..36b6beb181f6 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -3,7 +3,7 @@
*
* entry_32.S contains the system-call and low-level fault and trap handling routines.
*
- * Stack layout in 'syscall_exit':
+ * Stack layout while running C code:
* ptrace needs to have all registers on the stack.
* If the order here is changed, it needs to be
* updated in fork.c:copy_process(), signal.c:do_signal(),
@@ -211,7 +211,11 @@ ENTRY(ret_from_fork)
popl %eax
pushl $0x0202 # Reset kernel eflags
popfl
- jmp syscall_exit
+
+ /* When we fork, we trace the syscall return in the child, too. */
+ movl %esp, %eax
+ call syscall_return_slowpath
+ jmp restore_all
END(ret_from_fork)

ENTRY(ret_from_kernel_thread)
@@ -224,7 +228,15 @@ ENTRY(ret_from_kernel_thread)
movl PT_EBP(%esp), %eax
call *PT_EBX(%esp)
movl $0, PT_EAX(%esp)
- jmp syscall_exit
+
+ /*
+ * Kernel threads return to userspace as if returning from a syscall.
+ * We should check whether anything actually uses this path and, if so,
+ * consider switching it over to ret_from_fork.
+ */
+ movl %esp, %eax
+ call syscall_return_slowpath
+ jmp restore_all
ENDPROC(ret_from_kernel_thread)

/*
--
2.4.3

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