path: root/src/thread/x86_64
diff options
authorRich Felker <>2011-04-17 15:30:08 -0400
committerRich Felker <>2011-04-17 15:30:08 -0400
commit09dae2b7b66f741b30aa7ce95ab395239da20762 (patch)
treeda94ed95c914ec60663aec3368e3642d8c41cfeb /src/thread/x86_64
parentebf82447be4b30bedc19ad868c3a0662b1ba596d (diff)
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.
Diffstat (limited to 'src/thread/x86_64')
1 files changed, 6 insertions, 5 deletions
diff --git a/src/thread/x86_64/syscall_cp.s b/src/thread/x86_64/syscall_cp.s
index a36e8d1d..8b250488 100644
--- 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)
-2: xor %edi,%edi
- mov %rdi,8(%r10)
- mov %rdi,(%r10)
- dec %rdi
- jmp __cancel
+2: call __cancel