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Make forking off threads reliable on Windows

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This change makes posix_spawn_test no longer flaky on Windows, by (1)
fixing a race condition in wait(), and (2) removing a misguided vfork
implementation which was letting Windows bypass pthread_atfork().
This commit is contained in:
Justine Tunney 2023-07-30 08:55:01 -07:00
parent 2ebc5781a1
commit 58352df0a4
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GPG key ID: BE714B4575D6E328
30 changed files with 230 additions and 187 deletions
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48
libc/runtime/vfork.S
View file

@ -56,8 +56,18 @@
vfork:
.ftrace2
#ifdef __SANITIZE_ADDRESS__
jmp fork
#endif
#ifdef __x86_64__
#if SupportsWindows()
// these platforms disagree with vfork
testb $_HOSTXNU|_HOSTOPENBSD|_HOSTWINDOWS,__hostos(%rip)
jnz fork
#endif
#if !IsTiny()
push %rbp
mov %rsp,%rbp
@ -69,21 +79,6 @@ vfork:
pop %rbp
#endif
mov %fs:0,%r9 // get thread information block
#if SupportsWindows()
testb IsWindows()
jnz 6f // and we're lucky to have that
#endif
#ifdef __SANITIZE_ADDRESS__
jmp 5f // TODO: asan and vfork don't mix?
#endif
#if SupportsXnu()
testb IsXnu()
jnz 5f
#endif
#if SupportsOpenbsd()
testb IsOpenbsd()
jnz 5f // fake vfork plus msyscall issues
#endif
mov 0x3c(%r9),%r8d // avoid question of @vforksafe errno
pop %rsi // saves return address in a register
mov __NR_vfork(%rip),%eax
@ -106,29 +101,6 @@ vfork:
ret
.Lpar: andb $~TIB_FLAG_VFORKED,0x40(%r9)
ret
#if SupportsXnu() || SupportsOpenbsd() || defined(__SANITIZE_ADDRESS__)
5: push %rbp
mov %rsp,%rbp
push %r9
push %r9
call sys_fork
pop %r9
pop %r9
pop %rbp
jmp 1b
#endif
#if SupportsWindows()
6: push %rbp
mov %rsp,%rbp
push %r9
push %r9
xor %edi,%edi // dwCreationFlags
call sys_fork_nt
pop %r9
pop %r9
pop %rbp
jmp 1b
#endif
#elif defined(__aarch64__)