Revert "Revert "Lose the hand-written futex assembler.""

The problem with the original patch was that using syscall(3) means that
errno can be set, but pthread_create(3) was abusing the TLS errno slot as
a pthread_mutex_t for the thread startup handshake.

There was also a mistake in the check for syscall failures --- it should
have checked against -1 instead of 0 (not just because that's the default
idiom, but also here because futex(2) can legitimately return values > 0).

This patch stops abusing the TLS errno slot and adds a pthread_mutex_t to
pthread_internal_t instead. (Note that for LP64 sizeof(pthread_mutex_t) >
sizeof(uintptr_t), so we could potentially clobber other TLS slots too.)

I've also rewritten the LP32 compatibility stubs to directly reuse the
code from the .h file.

This reverts commit 75c55ff84ebfa686c7ae2cc8ee431c6a33bd46b4.

Bug: 15195455
Change-Id: I6ffb13e5cf6a35d8f59f692d94192aae9ab4593d

24 files changed, 45 insertions, 455 deletions

diff --git a/libc/SYSCALLS.TXT b/libc/SYSCALLS.TXT
index 60cf980..785d191 100644
--- a/libc/SYSCALLS.TXT
+++ b/libc/SYSCALLS.TXT
@@ -305,8 +305,6 @@ int eventfd:eventfd2(unsigned int, int)  all
 void _exit|_Exit:exit_group(int)  all
 void __exit:exit(int)  all
 
-int futex(void*, int, int, void*, void*, int)  all
-
 int inotify_init1(int)  all
 int inotify_add_watch(int, const char*, unsigned int)  all
 int inotify_rm_watch(int, unsigned int)  all
diff --git a/libc/arch-arm/arm.mk b/libc/arch-arm/arm.mk
index 3821854..c509b83 100644
--- a/libc/arch-arm/arm.mk
+++ b/libc/arch-arm/arm.mk
@@ -53,7 +53,6 @@ libc_bionic_src_files_arm += \
     arch-arm/bionic/__bionic_clone.S \
     arch-arm/bionic/eabi.c \
     arch-arm/bionic/_exit_with_stack_teardown.S \
-    arch-arm/bionic/futex_arm.S \
     arch-arm/bionic/__get_sp.S \
     arch-arm/bionic/libgcc_compat.c \
     arch-arm/bionic/memcmp16.S \
diff --git a/libc/arch-arm/bionic/futex_arm.S b/libc/arch-arm/bionic/futex_arm.S
deleted file mode 100644
index 89a1e96..0000000
--- a/libc/arch-arm/bionic/futex_arm.S
+++ /dev/null
@@ -1,38 +0,0 @@
-/*
- * Copyright (C) 2008 The Android Open Source Project
- * All rights reserved.
- *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions
- * are met:
- *  * Redistributions of source code must retain the above copyright
- *    notice, this list of conditions and the following disclaimer.
- *  * Redistributions in binary form must reproduce the above copyright
- *    notice, this list of conditions and the following disclaimer in
- *    the documentation and/or other materials provided with the
- *    distribution.
- *
- * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
- * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
- * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
- * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
- * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
- * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
- * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
- * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
- * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
- * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
- * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
- * SUCH DAMAGE.
- */
-
-#include <private/bionic_asm.h>
-
-// int __futex_syscall4(volatile void* ftx, int op, int val, const struct timespec* timeout)
-ENTRY_PRIVATE(__futex_syscall4)
-    mov     ip, r7
-    ldr     r7, =__NR_futex
-    swi     #0
-    mov     r7, ip
-    bx      lr
-END(__futex_syscall4)
diff --git a/libc/arch-arm/syscalls/futex.S b/libc/arch-arm/syscalls/futex.S
deleted file mode 100644
index 1646ca2..0000000
--- a/libc/arch-arm/syscalls/futex.S
+++ /dev/null
@@ -1,22 +0,0 @@
-/* Generated by gensyscalls.py. Do not edit. */
-
-#include <private/bionic_asm.h>
-
-ENTRY(futex)
-    mov     ip, sp
-    stmfd   sp!, {r4, r5, r6, r7}
-    .cfi_def_cfa_offset 16
-    .cfi_rel_offset r4, 0
-    .cfi_rel_offset r5, 4
-    .cfi_rel_offset r6, 8
-    .cfi_rel_offset r7, 12
-    ldmfd   ip, {r4, r5, r6}
-    ldr     r7, =__NR_futex
-    swi     #0
-    ldmfd   sp!, {r4, r5, r6, r7}
-    .cfi_def_cfa_offset 0
-    cmn     r0, #(MAX_ERRNO + 1)
-    bxls    lr
-    neg     r0, r0
-    b       __set_errno
-END(futex)
diff --git a/libc/arch-arm64/arm64.mk b/libc/arch-arm64/arm64.mk
index 7a9eb4e..93b0b0b 100644
--- a/libc/arch-arm64/arm64.mk
+++ b/libc/arch-arm64/arm64.mk
@@ -37,7 +37,6 @@ libc_bionic_src_files_arm64 := \
     arch-arm64/bionic/__bionic_clone.S \
     arch-arm64/bionic/bzero_arm64.c \
     arch-arm64/bionic/_exit_with_stack_teardown.S \
-    arch-arm64/bionic/futex_arm64.S \
     arch-arm64/bionic/__get_sp.S \
     arch-arm64/bionic/__rt_sigreturn.S \
     arch-arm64/bionic/_setjmp.S \
diff --git a/libc/arch-arm64/bionic/futex_arm64.S b/libc/arch-arm64/bionic/futex_arm64.S
deleted file mode 100644
index 9d7465a..0000000
--- a/libc/arch-arm64/bionic/futex_arm64.S
+++ /dev/null
@@ -1,47 +0,0 @@
-/*
- * Copyright (C) 2013 The Android Open Source Project
- * All rights reserved.
- *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions
- * are met:
- *  * Redistributions of source code must retain the above copyright
- *    notice, this list of conditions and the following disclaimer.
- *  * Redistributions in binary form must reproduce the above copyright
- *    notice, this list of conditions and the following disclaimer in
- *    the documentation and/or other materials provided with the
- *    distribution.
- *
- * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
- * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
- * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
- * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
- * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
- * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
- * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
- * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
- * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
- * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
- * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
- * SUCH DAMAGE.
- */
-
-#include <private/bionic_asm.h>
-
-// int __futex_syscall4(volatile void* ftx, int op, int val, const struct timespec* timeout)
-ENTRY_PRIVATE(__futex_syscall4)
-  stp x29, x30, [sp, #-16]!
-  .cfi_def_cfa_offset 16
-  .cfi_rel_offset x29, 0
-  .cfi_rel_offset x30, 8
-  mov x29, sp
-
-  mov x8, __NR_futex
-  svc #0
-
-  ldp x29, x30, [sp], #16
-  .cfi_def_cfa_offset 0
-  .cfi_restore x29
-  .cfi_restore x30
-  ret
-END(__futex_syscall4)
diff --git a/libc/arch-arm64/syscalls/futex.S b/libc/arch-arm64/syscalls/futex.S
deleted file mode 100644
index c14ebbf..0000000
--- a/libc/arch-arm64/syscalls/futex.S
+++ /dev/null
@@ -1,25 +0,0 @@
-/* Generated by gensyscalls.py. Do not edit. */
-
-#include <private/bionic_asm.h>
-
-ENTRY(futex)
-    stp     x29, x30, [sp, #-16]!
-    .cfi_def_cfa_offset 16
-    .cfi_rel_offset x29, 0
-    .cfi_rel_offset x30, 8
-    mov     x29,  sp
-
-    mov     x8, __NR_futex
-    svc     #0
-
-    ldp     x29, x30, [sp], #16
-    .cfi_def_cfa_offset 0
-    .cfi_restore x29
-    .cfi_restore x30
-
-    cmn     x0, #(MAX_ERRNO + 1)
-    cneg    x0, x0, hi
-    b.hi    __set_errno
-
-    ret
-END(futex)
diff --git a/libc/arch-mips/bionic/futex_mips.S b/libc/arch-mips/bionic/futex_mips.S
deleted file mode 100644
index 5a09f32..0000000
--- a/libc/arch-mips/bionic/futex_mips.S
+++ /dev/null
@@ -1,50 +0,0 @@
-/*
- * Copyright (C) 2008 The Android Open Source Project
- * All rights reserved.
- *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions
- * are met:
- *  * Redistributions of source code must retain the above copyright
- *    notice, this list of conditions and the following disclaimer.
- *  * Redistributions in binary form must reproduce the above copyright
- *    notice, this list of conditions and the following disclaimer in
- *    the documentation and/or other materials provided with the
- *    distribution.
- *
- * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
- * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
- * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
- * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
- * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
- * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
- * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
- * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
- * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
- * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
- * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
- * SUCH DAMAGE.
- */
-
-#include <private/bionic_asm.h>
-
-// int __futex_syscall4(volatile void* ftx, int op, int val, const struct timespec* timeout)
-ENTRY_PRIVATE(__futex_syscall4)
-	subu	sp,4*6
-	sw	$0,20(sp)	/* val3 */
-	sw	$0,16(sp)	/* addr2 */
-#	move	a3,a3		/* timespec */
-#	move	a2,a2		/* val */
-#	li	a1,a1		/* op */
-#	move	a0,a0		/* ftx */
-	li	v0,__NR_futex
-	syscall
-	.set noreorder
-	bnez	a3, 1f		/* Check for error */
-         neg	v0		/* Negate error number if it's valid */
-	move	v0,$0		/* Otherwise return 0 */
-1:
-	.set reorder
-	addu	sp,4*6
-	j	ra
-END(__futex_syscall4)
diff --git a/libc/arch-mips/mips.mk b/libc/arch-mips/mips.mk
index d7d1df4..2c87a9e 100644
--- a/libc/arch-mips/mips.mk
+++ b/libc/arch-mips/mips.mk
@@ -58,7 +58,6 @@ libc_bionic_src_files_mips += \
     arch-mips/bionic/bzero.S \
     arch-mips/bionic/cacheflush.cpp \
     arch-mips/bionic/_exit_with_stack_teardown.S \
-    arch-mips/bionic/futex_mips.S \
     arch-mips/bionic/__get_sp.S \
     arch-mips/bionic/memcmp16.S \
     arch-mips/bionic/_setjmp.S \
diff --git a/libc/arch-mips/syscalls/futex.S b/libc/arch-mips/syscalls/futex.S
deleted file mode 100644
index a865fea..0000000
--- a/libc/arch-mips/syscalls/futex.S
+++ /dev/null
@@ -1,19 +0,0 @@
-/* Generated by gensyscalls.py. Do not edit. */
-
-#include <private/bionic_asm.h>
-
-ENTRY(futex)
-    .set noreorder
-    .cpload t9
-    li v0, __NR_futex
-    syscall
-    bnez a3, 1f
-    move a0, v0
-    j ra
-    nop
-1:
-    la t9,__set_errno
-    j t9
-    nop
-    .set reorder
-END(futex)
diff --git a/libc/arch-mips64/bionic/futex_mips.S b/libc/arch-mips64/bionic/futex_mips.S
deleted file mode 100644
index 60c218c..0000000
--- a/libc/arch-mips64/bionic/futex_mips.S
+++ /dev/null
@@ -1,64 +0,0 @@
-/*
- * Copyright (C) 2008 The Android Open Source Project
- * All rights reserved.
- *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions
- * are met:
- *  * Redistributions of source code must retain the above copyright
- *    notice, this list of conditions and the following disclaimer.
- *  * Redistributions in binary form must reproduce the above copyright
- *    notice, this list of conditions and the following disclaimer in
- *    the documentation and/or other materials provided with the
- *    distribution.
- *
- * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
- * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
- * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
- * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
- * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
- * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
- * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
- * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
- * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
- * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
- * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
- * SUCH DAMAGE.
- */
-
-#include <private/bionic_asm.h>
-
-#if (_MIPS_SIM == _ABIO32) || (_MIPS_SIM == _ABI32)
-FRAMESZ		=	MKFSIZ(NARGSAVE+2,0)
-FRAME_A4	=	4*REGSZ
-FRAME_A5	=	5*REGSZ
-#else
-FRAMESZ		=	0
-#endif
-
-// int __futex_syscall4(volatile void* ftx, int op, int val, const struct timespec* timeout)
-LEAF(__futex_syscall4,FRAMESZ)
-#if (_MIPS_SIM == _ABIO32) || (_MIPS_SIM == _ABI32)
-	PTR_SUBU sp, FRAMESZ
-	REG_S	$0,FRAME_A5(sp)	/* val3 */
-	REG_S	$0,FRAME_A4(sp)	/* addr2 */
-#else
-	move	a5,$0		/* val3 */
-	move	a4,$0		/* addr2 */
-#endif
-#	move	a3,a3		/* timespec */
-#	move	a2,a2		/* val */
-#	move	a1,a1		/* op */
-#	move	a0,a0		/* ftx */
-	LI	v0,__NR_futex
-	syscall
-	neg	v0		/* Negate errno */
-	bnez	a3,1f		/* Check for error */
-	move	v0,$0		/* Return 0 if no error */
-1:
-#if (_MIPS_SIM == _ABIO32) || (_MIPS_SIM == _ABI32)
-	PTR_ADDU sp,FRAMESZ
-#endif
-	j	ra
-	END(__futex_syscall4)
-.hidden __futex_syscall4
diff --git a/libc/arch-mips64/mips64.mk b/libc/arch-mips64/mips64.mk
index b6e0209..26390a6 100644
--- a/libc/arch-mips64/mips64.mk
+++ b/libc/arch-mips64/mips64.mk
@@ -43,7 +43,6 @@ libc_bionic_src_files_mips64 := \
     arch-mips64/bionic/__bionic_clone.S \
     arch-mips64/bionic/bzero.S \
     arch-mips64/bionic/_exit_with_stack_teardown.S \
-    arch-mips64/bionic/futex_mips.S \
     arch-mips64/bionic/__get_sp.S \
     arch-mips64/bionic/getdents.cpp \
     arch-mips64/bionic/memcmp16.S \
diff --git a/libc/arch-mips64/syscalls/futex.S b/libc/arch-mips64/syscalls/futex.S
deleted file mode 100644
index dc7dcc6..0000000
--- a/libc/arch-mips64/syscalls/futex.S
+++ /dev/null
@@ -1,25 +0,0 @@
-/* Generated by gensyscalls.py. Do not edit. */
-
-#include <private/bionic_asm.h>
-
-ENTRY(futex)
-    .set push
-    .set noreorder
-    li v0, __NR_futex
-    syscall
-    bnez a3, 1f
-    move a0, v0
-    j ra
-    nop
-1:
-    move t0, ra
-    bal     2f
-    nop
-2:
-    .cpsetup ra, t1, 2b
-    LA t9,__set_errno
-    .cpreturn
-    j t9
-    move ra, t0
-    .set pop
-END(futex)
diff --git a/libc/arch-x86/bionic/futex_x86.S b/libc/arch-x86/bionic/futex_x86.S
deleted file mode 100644
index 94647ca..0000000
--- a/libc/arch-x86/bionic/futex_x86.S
+++ /dev/null
@@ -1,16 +0,0 @@
-#include <private/bionic_asm.h>
-
-// int __futex_syscall4(volatile void* ftx, int op, int val, const struct timespec* timeout)
-ENTRY_PRIVATE(__futex_syscall4)
-    pushl   %ebx
-    pushl   %esi
-    movl    12(%esp), %ebx      /* ftx */
-    movl    16(%esp), %ecx      /* op */
-    movl    20(%esp), %edx      /* val */
-    movl    24(%esp), %esi      /* timeout */
-    movl    $__NR_futex, %eax
-    int     $0x80
-    popl    %esi
-    popl    %ebx
-    ret
-END(__futex_syscall4)
diff --git a/libc/arch-x86/syscalls/futex.S b/libc/arch-x86/syscalls/futex.S
deleted file mode 100644
index 7a52913..0000000
--- a/libc/arch-x86/syscalls/futex.S
+++ /dev/null
@@ -1,42 +0,0 @@
-/* Generated by gensyscalls.py. Do not edit. */
-
-#include <private/bionic_asm.h>
-
-ENTRY(futex)
-    pushl   %ebx
-    pushl   %ecx
-    pushl   %edx
-    pushl   %esi
-    pushl   %edi
-    pushl   %ebp
-    .cfi_def_cfa_offset 24
-    .cfi_rel_offset ebx, 0
-    .cfi_rel_offset ecx, 4
-    .cfi_rel_offset edx, 8
-    .cfi_rel_offset esi, 12
-    .cfi_rel_offset edi, 16
-    .cfi_rel_offset ebp, 20
-    mov     28(%esp), %ebx
-    mov     32(%esp), %ecx
-    mov     36(%esp), %edx
-    mov     40(%esp), %esi
-    mov     44(%esp), %edi
-    mov     48(%esp), %ebp
-    movl    $__NR_futex, %eax
-    int     $0x80
-    cmpl    $-MAX_ERRNO, %eax
-    jb      1f
-    negl    %eax
-    pushl   %eax
-    call    __set_errno
-    addl    $4, %esp
-    orl     $-1, %eax
-1:
-    popl    %ebp
-    popl    %edi
-    popl    %esi
-    popl    %edx
-    popl    %ecx
-    popl    %ebx
-    ret
-END(futex)
diff --git a/libc/arch-x86/x86.mk b/libc/arch-x86/x86.mk
index 34da0ce..aa183cb 100644
--- a/libc/arch-x86/x86.mk
+++ b/libc/arch-x86/x86.mk
@@ -23,7 +23,6 @@ libc_bionic_src_files_x86 := \
 libc_bionic_src_files_x86 += \
     arch-x86/bionic/__bionic_clone.S \
     arch-x86/bionic/_exit_with_stack_teardown.S \
-    arch-x86/bionic/futex_x86.S \
     arch-x86/bionic/__get_sp.S \
     arch-x86/bionic/_setjmp.S \
     arch-x86/bionic/setjmp.S \
diff --git a/libc/arch-x86_64/bionic/futex_x86_64.S b/libc/arch-x86_64/bionic/futex_x86_64.S
deleted file mode 100644
index c248439..0000000
--- a/libc/arch-x86_64/bionic/futex_x86_64.S
+++ /dev/null
@@ -1,37 +0,0 @@
-/*
- * Copyright (C) 2013 The Android Open Source Project
- * All rights reserved.
- *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions
- * are met:
- *  * Redistributions of source code must retain the above copyright
- *    notice, this list of conditions and the following disclaimer.
- *  * Redistributions in binary form must reproduce the above copyright
- *    notice, this list of conditions and the following disclaimer in
- *    the documentation and/or other materials provided with the
- *    distribution.
- *
- * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
- * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
- * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
- * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
- * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
- * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
- * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
- * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
- * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
- * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
- * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
- * SUCH DAMAGE.
- */
-
-#include <private/bionic_asm.h>
-
-// int __futex_syscall4(volatile void* ftx, int op, int val, const struct timespec* timeout)
-ENTRY_PRIVATE(__futex_syscall4)
-    mov     %rcx, %r10      /* timeout */
-    mov     $__NR_futex, %eax
-    syscall
-    ret
-END(__futex_syscall4)
diff --git a/libc/arch-x86_64/syscalls/futex.S b/libc/arch-x86_64/syscalls/futex.S
deleted file mode 100644
index 62f64bd..0000000
--- a/libc/arch-x86_64/syscalls/futex.S
+++ /dev/null
@@ -1,17 +0,0 @@
-/* Generated by gensyscalls.py. Do not edit. */
-
-#include <private/bionic_asm.h>
-
-ENTRY(futex)
-    movq    %rcx, %r10
-    movl    $__NR_futex, %eax
-    syscall
-    cmpq    $-MAX_ERRNO, %rax
-    jb      1f
-    negl    %eax
-    movl    %eax, %edi
-    call    __set_errno
-    orq     $-1, %rax
-1:
-    ret
-END(futex)
diff --git a/libc/arch-x86_64/x86_64.mk b/libc/arch-x86_64/x86_64.mk
index 2bcf432..e3c2562 100644
--- a/libc/arch-x86_64/x86_64.mk
+++ b/libc/arch-x86_64/x86_64.mk
@@ -30,7 +30,6 @@ libc_common_src_files_x86_64 += \
 libc_bionic_src_files_x86_64 := \
     arch-x86_64/bionic/__bionic_clone.S \
     arch-x86_64/bionic/_exit_with_stack_teardown.S \
-    arch-x86_64/bionic/futex_x86_64.S \
     arch-x86_64/bionic/__get_sp.S \
     arch-x86_64/bionic/__rt_sigreturn.S \
     arch-x86_64/bionic/_setjmp.S \
diff --git a/libc/bionic/ndk_cruft.cpp b/libc/bionic/ndk_cruft.cpp
index 4900a8a..1284b9a 100644
--- a/libc/bionic/ndk_cruft.cpp
+++ b/libc/bionic/ndk_cruft.cpp
@@ -31,7 +31,6 @@
 
 #include <ctype.h>
 #include <inttypes.h>
-#include <linux/futex.h>
 #include <pthread.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -201,25 +200,20 @@ extern "C" int vfdprintf(int fd, const char* fmt, va_list ap) {
   return vdprintf(fd, fmt, ap);
 }
 
-static inline int __futex(volatile void* ftx, int op, int value, const struct timespec* timeout) {
-  // Our generated syscall assembler sets errno, but our callers (pthread functions) don't want to.
-  int saved_errno = errno;
-  if (syscall(__NR_futex, ftx, op, value, timeout) == 0) {
-    return 0;
-  }
-  int result = -errno;
-  errno = saved_errno;
-  return result;
-}
+#define __futex_wake __real_futex_wake
+#define __futex_wait __real_futex_wait
+#include "private/bionic_futex.h"
+#undef __futex_wake
+#undef __futex_wait
 
 // This used to be in <sys/atomics.h>.
 extern "C" int __futex_wake(volatile void* ftx, int count) {
-  return __futex(ftx, FUTEX_WAKE, count, NULL);
+  return __real_futex_wake(ftx, count);
 }
 
 // This used to be in <sys/atomics.h>.
 extern "C" int __futex_wait(volatile void* ftx, int value, const struct timespec* timeout) {
-  return __futex(ftx, FUTEX_WAIT, value, timeout);
+  return __real_futex_wait(ftx, value, timeout);
 }
 
 // Unity's libmono uses this.
diff --git a/libc/bionic/pthread_create.cpp b/libc/bionic/pthread_create.cpp
index 303af81..c4cb262 100644
--- a/libc/bionic/pthread_create.cpp
+++ b/libc/bionic/pthread_create.cpp
@@ -144,10 +144,8 @@ static int __pthread_start(void* arg) {
   // notify gdb about this thread before we start doing anything.
   // This also provides the memory barrier needed to ensure that all memory
   // accesses previously made by the creating thread are visible to us.
-  pthread_mutex_t* start_mutex = (pthread_mutex_t*) &thread->tls[TLS_SLOT_START_MUTEX];
-  pthread_mutex_lock(start_mutex);
-  pthread_mutex_destroy(start_mutex);
-  thread->tls[TLS_SLOT_START_MUTEX] = NULL;
+  pthread_mutex_lock(&thread->startup_handshake_mutex);
+  pthread_mutex_destroy(&thread->startup_handshake_mutex);
 
   __init_alternate_signal_stack(thread);
 
@@ -204,7 +202,8 @@ int pthread_create(pthread_t* thread_out, pthread_attr_t const* attr,
   // The child stack is the same address, just growing in the opposite direction.
   // At offsets >= 0, we have the TLS slots.
   // At offsets < 0, we have the child stack.
-  thread->tls = (void**)((uint8_t*)(thread->attr.stack_base) + thread->attr.stack_size - BIONIC_TLS_SLOTS * sizeof(void*));
+  thread->tls = reinterpret_cast<void**>(reinterpret_cast<uint8_t*>(thread->attr.stack_base) +
+                                         thread->attr.stack_size - BIONIC_TLS_SLOTS * sizeof(void*));
   void* child_stack = thread->tls;
   __init_tls(thread);
 
@@ -214,9 +213,8 @@ int pthread_create(pthread_t* thread_out, pthread_attr_t const* attr,
   // This also provides the memory barrier we need to ensure that all
   // memory accesses previously performed by this thread are visible to
   // the new thread.
-  pthread_mutex_t* start_mutex = (pthread_mutex_t*) &thread->tls[TLS_SLOT_START_MUTEX];
-  pthread_mutex_init(start_mutex, NULL);
-  pthread_mutex_lock(start_mutex);
+  pthread_mutex_init(&thread->startup_handshake_mutex, NULL);
+  pthread_mutex_lock(&thread->startup_handshake_mutex);
 
   thread->start_routine = start_routine;
   thread->start_routine_arg = arg;
@@ -237,7 +235,7 @@ int pthread_create(pthread_t* thread_out, pthread_attr_t const* attr,
     // We don't have to unlock the mutex at all because clone(2) failed so there's no child waiting to
     // be unblocked, but we're about to unmap the memory the mutex is stored in, so this serves as a
     // reminder that you can't rewrite this function to use a ScopedPthreadMutexLocker.
-    pthread_mutex_unlock(start_mutex);
+    pthread_mutex_unlock(&thread->startup_handshake_mutex);
     if ((thread->attr.flags & PTHREAD_ATTR_FLAG_USER_ALLOCATED_STACK) == 0) {
       munmap(thread->attr.stack_base, thread->attr.stack_size);
     }
@@ -252,7 +250,7 @@ int pthread_create(pthread_t* thread_out, pthread_attr_t const* attr,
     // Letting the thread run is the easiest way to clean up its resources.
     thread->attr.flags |= PTHREAD_ATTR_FLAG_DETACHED;
     thread->start_routine = __do_nothing;
-    pthread_mutex_unlock(start_mutex);
+    pthread_mutex_unlock(&thread->startup_handshake_mutex);
     return init_errno;
   }
 
@@ -264,7 +262,7 @@ int pthread_create(pthread_t* thread_out, pthread_attr_t const* attr,
 
   // Publish the pthread_t and unlock the mutex to let the new thread start running.
   *thread_out = reinterpret_cast<pthread_t>(thread);
-  pthread_mutex_unlock(start_mutex);
+  pthread_mutex_unlock(&thread->startup_handshake_mutex);
 
   return 0;
 }
diff --git a/libc/bionic/pthread_internal.h b/libc/bionic/pthread_internal.h
index 295d9d6..490ae86 100644
--- a/libc/bionic/pthread_internal.h
+++ b/libc/bionic/pthread_internal.h
@@ -48,6 +48,8 @@ struct pthread_internal_t {
 
   void* alternate_signal_stack;
 
+  pthread_mutex_t startup_handshake_mutex;
+
   /*
    * The dynamic linker implements dlerror(3), which makes it hard for us to implement this
    * per-thread buffer by simply using malloc(3) and free(3).
diff --git a/libc/private/bionic_futex.h b/libc/private/bionic_futex.h
index 11699ce..35d33d0 100644
--- a/libc/private/bionic_futex.h
+++ b/libc/private/bionic_futex.h
@@ -28,31 +28,42 @@
 #ifndef _BIONIC_FUTEX_H
 #define _BIONIC_FUTEX_H
 
+#include <errno.h>
 #include <linux/futex.h>
-#include <sys/cdefs.h>
 #include <stdbool.h>
 #include <stddef.h>
+#include <sys/cdefs.h>
+#include <sys/syscall.h>
 
 __BEGIN_DECLS
 
 struct timespec;
 
-extern int __futex_syscall4(volatile void* ftx, int op, int value, const struct timespec* timeout);
+static inline __always_inline int __futex(volatile void* ftx, int op, int value, const struct timespec* timeout) {
+  // Our generated syscall assembler sets errno, but our callers (pthread functions) don't want to.
+  int saved_errno = errno;
+  if (__predict_false(syscall(__NR_futex, ftx, op, value, timeout) == -1)) {
+    int result = -errno;
+    errno = saved_errno;
+    return result;
+  }
+  return 0;
+}
 
 static inline int __futex_wake(volatile void* ftx, int count) {
-  return __futex_syscall4(ftx, FUTEX_WAKE, count, NULL);
+  return __futex(ftx, FUTEX_WAKE, count, NULL);
 }
 
 static inline int __futex_wake_ex(volatile void* ftx, bool shared, int count) {
-  return __futex_syscall4(ftx, shared ? FUTEX_WAKE : FUTEX_WAKE_PRIVATE, count, NULL);
+  return __futex(ftx, shared ? FUTEX_WAKE : FUTEX_WAKE_PRIVATE, count, NULL);
 }
 
 static inline int __futex_wait(volatile void* ftx, int value, const struct timespec* timeout) {
-  return __futex_syscall4(ftx, FUTEX_WAIT, value, timeout);
+  return __futex(ftx, FUTEX_WAIT, value, timeout);
 }
 
 static inline int __futex_wait_ex(volatile void* ftx, bool shared, int value, const struct timespec* timeout) {
-  return __futex_syscall4(ftx, shared ? FUTEX_WAIT : FUTEX_WAIT_PRIVATE, value, timeout);
+  return __futex(ftx, shared ? FUTEX_WAIT : FUTEX_WAIT_PRIVATE, value, timeout);
 }
 
 __END_DECLS
diff --git a/libc/private/bionic_tls.h b/libc/private/bionic_tls.h
index c2cf196..b52013f 100644
--- a/libc/private/bionic_tls.h
+++ b/libc/private/bionic_tls.h
@@ -46,32 +46,27 @@ __BEGIN_DECLS
  ** pre-allocated slot directly for performance reason).
  **/
 
-/* Well-known TLS slots. What data goes in which slot is arbitrary unless otherwise noted. */
+// Well-known TLS slots. What data goes in which slot is arbitrary unless otherwise noted.
 enum {
-  TLS_SLOT_SELF = 0, /* The kernel requires this specific slot for x86. */
+  TLS_SLOT_SELF = 0, // The kernel requires this specific slot for x86.
   TLS_SLOT_THREAD_ID,
   TLS_SLOT_ERRNO,
 
-  /* This slot in the child's TLS is used to synchronize the parent and child
-   * during thread initialization. The child finishes with this mutex before
-   * running any code that can set errno, so we can reuse the errno slot. */
-  TLS_SLOT_START_MUTEX = TLS_SLOT_ERRNO,
-
-  /* These two aren't used by bionic itself, but allow the graphics code to
-   * access TLS directly rather than using the pthread API. */
+  // These two aren't used by bionic itself, but allow the graphics code to
+  // access TLS directly rather than using the pthread API.
   TLS_SLOT_OPENGL_API = 3,
   TLS_SLOT_OPENGL = 4,
 
-  /* This slot is only used to pass information from the dynamic linker to
-   * libc.so when the C library is loaded in to memory. The C runtime init
-   * function will then clear it. Since its use is extremely temporary,
-   * we reuse an existing location that isn't needed during libc startup. */
+  // This slot is only used to pass information from the dynamic linker to
+  // libc.so when the C library is loaded in to memory. The C runtime init
+  // function will then clear it. Since its use is extremely temporary,
+  // we reuse an existing location that isn't needed during libc startup.
   TLS_SLOT_BIONIC_PREINIT = TLS_SLOT_OPENGL_API,
 
-  TLS_SLOT_STACK_GUARD = 5, /* GCC requires this specific slot for x86. */
+  TLS_SLOT_STACK_GUARD = 5, // GCC requires this specific slot for x86.
   TLS_SLOT_DLERROR,
 
-  TLS_SLOT_FIRST_USER_SLOT /* Must come last! */
+  TLS_SLOT_FIRST_USER_SLOT // Must come last!
 };
 
 /*