Add syscall buffering for the new glibc syscall wrapper.

glibc reworked the code for async-cancelable syscalls:
bminor/glibc@89b5307

Author: rocallahan

src/preload/syscall_hook.S

@@ -664,6 +664,11 @@ SYSCALLHOOK_START(_syscall_hook_trampoline_48_89_e5)
         callq __morestack
 SYSCALLHOOK_END(_syscall_hook_trampoline_48_89_e5)
 
+SYSCALLHOOK_START(_syscall_hook_trampoline_48_8b_45_10)
+        mov    0x10(%rbp),%rax
+        callq __morestack
+SYSCALLHOOK_END(_syscall_hook_trampoline_48_8b_45_10)
+
 SYSCALLHOOK_START(_syscall_hook_trampoline_48_89_fb)
         mov %rdi,%rbx
         callq __morestack

src/preload/syscallbuf.c

@@ -829,6 +829,7 @@ static void __attribute__((constructor)) init_process(void) {
   extern RR_HIDDEN void _syscall_hook_trampoline_4c_8b_0d(void);
   extern RR_HIDDEN void _syscall_hook_trampoline_48_89_e5(void);
   extern RR_HIDDEN void _syscall_hook_trampoline_48_89_fb(void);
+  extern RR_HIDDEN void _syscall_hook_trampoline_48_8b_45_10(void);
   extern RR_HIDDEN void _syscall_hook_trampoline_48_8d_b3_f0_08_00_00(void);
   extern RR_HIDDEN void _syscall_hook_trampoline_nops(void);
 
@@ -1060,6 +1061,11 @@ static void __attribute__((constructor)) init_process(void) {
       3,
       { 0x48, 0x89, 0xfb },
       (uintptr_t)_syscall_hook_trampoline_48_89_fb },
+    /* glibc-2.41-5.fc42.x86_64 has 'mov 0x10(%rbp),%rax' followed by 'syscall' */
+    { PATCH_SYSCALL_INSTRUCTION_IS_LAST,
+      4,
+      { 0x48, 0x8b, 0x45, 0x10 },
+      (uintptr_t)_syscall_hook_trampoline_48_8b_45_10 },
     /* Support explicit 5 byte nop (`nopl 0(%ax, %ax, 1)`) before 'rdtsc' or syscall (may ignore interfering branches) */
     { PATCH_SYSCALL_INSTRUCTION_IS_LAST |
       PATCH_IS_NOP_INSTRUCTIONS,

src/test/x86/morestack_unwind.c

@@ -8,6 +8,9 @@ static void breakpoint(void) {
 }
 
 int main(void) {
+  // glibc write() might only be patched after the first time it is executed.
+  atomic_puts("Ensure glibc write() is patched...");
+  // The test requires this write() be buffered:
   atomic_puts("EXIT-SUCCESS");
   breakpoint();
   return 0;