fix bugs in cancellable syscall asm

x86_64 was just plain wrong in the cancel-flag-already-set path, and
crashing.

the more subtle error was not clearing the saved stack pointer before
returning to c code. this could result in the signal handler
misidentifying c code as the pre-syscall part of the asm, and acting
on cancellation at the wrong time, and thus resource leak race
conditions.

also, now __cancel (in the c code) is responsible for clearing the
saved sp in the already-cancelled branch. this means we have to use
call rather than jmp to ensure the stack pointer in the c will never
match what the asm saved.

diff --git a/src/thread/cancel_impl.c b/src/thread/cancel_impl.c
index 7bcfaef..2d2bb57 100644 (file)
--- a/src/thread/cancel_impl.c
+++ b/src/thread/cancel_impl.c
@@ -3,6 +3,7 @@
 void __cancel()
 {
        pthread_t self = __pthread_self();
+       self->cp_sp = 0;
        self->canceldisable = 1;
        self->cancelasync = 0;
        pthread_exit(PTHREAD_CANCELED);
@@ -24,8 +25,8 @@ long (__syscall_cp)(long nr, long u, long v, long w, long x, long y, long z)
        self->cp_sp = 0;
        self->cp_ip = 0;
        r = __syscall_cp_asm(&self->cp_sp, nr, u, v, w, x, y, z);
-       self->cp_sp = old_sp;
        self->cp_ip = old_ip;
+       self->cp_sp = old_sp;
        if (r == -EINTR && self->cancel) __cancel();
        return r;
 }

diff --git a/src/thread/i386/syscall_cp.s b/src/thread/i386/syscall_cp.s
index 6d8c354..5190513 100644 (file)
--- a/src/thread/i386/syscall_cp.s
+++ b/src/thread/i386/syscall_cp.s
@@ -28,9 +28,8 @@ __syscall_cp_asm:
        popl %edi
        popl %esi
        popl %ebx
+       xorl %edx,%edx
+       movl 4(%esp),%ecx
+       movl %edx,(%ecx)
        ret
-2:     xorl %eax,%eax
-       movl %eax,4(%ecx)
-       movl %eax,(%ecx)
-       pushl $-1
-       call __cancel
+2:     call __cancel

diff --git a/src/thread/x86_64/syscall_cp.s b/src/thread/x86_64/syscall_cp.s
index a36e8d1..8b25048 100644 (file)
--- a/src/thread/x86_64/syscall_cp.s
+++ b/src/thread/x86_64/syscall_cp.s
@@ -8,6 +8,7 @@ __syscall_cp_asm:
        mov 16(%rdi),%eax
        test %eax,%eax
        jnz 2f
+       mov %rdi,%r11
        mov %rsi,%rax
        mov %rdx,%rdi
        mov %rcx,%rsi
@@ -15,10 +16,10 @@ __syscall_cp_asm:
        mov %r9,%r10
        mov 8(%rsp),%r8
        mov 16(%rsp),%r9
+       mov %r11,8(%rsp)
 1:     syscall
+       xor %ecx,%ecx
+       mov 8(%rsp),%edi
+       mov %rcx,(%rdi)
        ret
-2:     xor %edi,%edi
-       mov %rdi,8(%r10)
-       mov %rdi,(%r10)
-       dec %rdi
-       jmp __cancel
+2:     call __cancel