Track whether a thread is currently vforked.
Our various fd debugging facilities get extremely confused by a vforked
process closing file descriptors in preparation to exec: fdsan can
abort, and fdtrack will delete backtraces for any file descriptors that
get closed. Keep track of whether we're in a vforked child in order to
be able to detect this.
Bug: http://b/153926671
Test: 32/64-bit bionic-unit-tests on blueline, x86_64 emulator
Change-Id: I8a082fd06bfdfef0e2a88dbce350b6f667f7df9f
diff --git a/libc/arch-x86/bionic/vfork.S b/libc/arch-x86/bionic/vfork.S
index 663169c..231a36e 100644
--- a/libc/arch-x86/bionic/vfork.S
+++ b/libc/arch-x86/bionic/vfork.S
@@ -37,13 +37,25 @@
.cfi_adjust_cfa_offset 4
.cfi_rel_offset ecx, 0
- // __get_tls()[TLS_SLOT_THREAD_ID]->cached_pid_ = 0
+ // Set cached_pid_ to 0, vforked_ to 1, and stash the previous value.
movl %gs:0, %eax
movl (TLS_SLOT_THREAD_ID * 4)(%eax), %eax
- movl $0, 12(%eax)
+ movl 12(%eax), %edx
+ movl $0x80000000, 12(%eax)
movl $__NR_vfork, %eax
int $0x80
+
+ test %eax, %eax
+ jz 1f
+
+ // rc != 0: restore the previous cached_pid_/vforked_ values.
+ pushl %ecx
+ movl %gs:0, %ecx
+ movl (TLS_SLOT_THREAD_ID * 4)(%ecx), %ecx
+ movl %edx, 12(%ecx)
+ popl %ecx
+
cmpl $-MAX_ERRNO, %eax
jb 1f
negl %eax