[RFC PATCH 2/2] x86_64: Check for AST when exiting a syscall

[Sergey Bugaev]

...like it's already done when exiting a trap. This is required, since
handing a syscall can result in an AST; in particular this happens when
the current thread is being terminated, which sets AST_TERMINATE and
expects the thread to never return to userspace.

Fixes a kernel crash upon calling exit () or pthread_exit () in glibc.
---
 x86_64/locore.S | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/x86_64/locore.S b/x86_64/locore.S
index 366ef292..577a9096 100644
--- a/x86_64/locore.S
+++ b/x86_64/locore.S
@@ -1428,10 +1428,17 @@ _syscall64_args_stack:
 
 _syscall64_call:
        call    *EXT(mach_trap_table)+8(%rax)  /* call procedure */
-       // XXX: check ast on exit?
 
-       /* Restore thread state and return to user using sysret. */
+_syscall64_check_for_ast:
+       /* Check for ast. */
        CPU_NUMBER(%r11)
+       cmpl    $0,CX(EXT(need_ast),%r11)
+       jz      _syscall64_restore_state
+       call    EXT(i386_astintr)
+       jmp     _syscall64_check_for_ast        /* check again */
+
+_syscall64_restore_state:
+       /* Restore thread state and return to user using sysret. */
        movq    CX(EXT(active_threads),%r11),%r11 /* point to current thread */
        movq    TH_PCB(%r11),%r11               /* point to pcb */
        addq    $ PCB_ISS,%r11                  /* point to saved state */
-- 
2.40.1