[libc] Add __attribute__((always_inline)) to x86_64 syscall functions.

Summary:
Some syscalls like SYS_clone do not tolerate a return instruction after
the syscall instruction. Marking the syscall functions with the
`always_inline` attribute accommodates such syscalls as inlining
eliminates the return instruction.

Reviewers: abrachet, phosek

Subscribers: MaskRay, tschuett, libc-commits

Tags: #libc-project

Differential Revision: https://reviews.llvm.org/D72102

1 files changed, 14 insertions, 10 deletions

diff --git a/libc/config/linux/x86_64/syscall.h.inc b/libc/config/linux/x86_64/syscall.h.inc
index 944ac99e51a..33f211ca199 100644
--- a/libc/config/linux/x86_64/syscall.h.inc
+++ b/libc/config/linux/x86_64/syscall.h.inc
@@ -1,4 +1,4 @@
-//===------------ inline implementation of x86_64 syscalls --------------*-===//
+//===------------ inline implementation of x86_64 syscalls ----------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -14,7 +14,7 @@
 
 namespace __llvm_libc {
 
-inline long syscall(long __number) {
+__attribute__((always_inline)) inline long syscall(long __number) {
   long retcode;
   LIBC_INLINE_ASM("syscall" :
              "=a"(retcode) :
@@ -23,7 +23,7 @@ inline long syscall(long __number) {
   return retcode;
 }
 
-inline long syscall(long __number, long __arg1) {
+__attribute__((always_inline)) inline long syscall(long __number, long __arg1) {
   long retcode;
   LIBC_INLINE_ASM("syscall" :
              "=a"(retcode) :
@@ -32,7 +32,8 @@ inline long syscall(long __number, long __arg1) {
   return retcode;
 }
 
-inline long syscall(long __number, long __arg1, long __arg2) {
+__attribute__((always_inline)) inline long syscall(
+    long __number, long __arg1, long __arg2) {
   long retcode;
   LIBC_INLINE_ASM("syscall" :
              "=a"(retcode) :
@@ -41,7 +42,8 @@ inline long syscall(long __number, long __arg1, long __arg2) {
   return retcode;
 }
 
-inline long syscall(long __number, long __arg1, long __arg2, long __arg3) {
+__attribute__((always_inline)) inline long syscall(
+    long __number, long __arg1, long __arg2, long __arg3) {
   long retcode;
   LIBC_INLINE_ASM("syscall" :
              "=a"(retcode) :
@@ -50,7 +52,7 @@ inline long syscall(long __number, long __arg1, long __arg2, long __arg3) {
   return retcode;
 }
 
-inline long syscall(
+__attribute__((always_inline)) inline long syscall(
     long __number, long __arg1, long __arg2, long __arg3, long __arg4) {
   long retcode;
   register long r10 __asm__("r10") = __arg4;
@@ -61,8 +63,9 @@ inline long syscall(
   return retcode;
 }
 
-inline long syscall(long __number, long __arg1, long __arg2, long __arg3,
-                    long __arg4, long __arg5) {
+__attribute__((always_inline)) inline long syscall(
+    long __number, long __arg1, long __arg2, long __arg3, long __arg4,
+    long __arg5) {
   long retcode;
   register long r10 __asm__("r10") = __arg4;
   register long r8 __asm__("r8") = __arg5;
@@ -74,8 +77,9 @@ inline long syscall(long __number, long __arg1, long __arg2, long __arg3,
   return retcode;
 }
 
-inline long syscall(long __number, long __arg1, long __arg2, long __arg3,
-                    long __arg4, long __arg5, long __arg6) {
+__attribute__((always_inline)) inline long syscall(
+    long __number, long __arg1, long __arg2, long __arg3, long __arg4,
+    long __arg5, long __arg6) {
   long retcode;
   register long r10 __asm__("r10") = __arg4;
   register long r8 __asm__("r8") = __arg5;