Make sure that VDSO patch code is properly aligned

The code that is injected into the tracee processes' VDSO needs to be 8
byte aligned in order to satisfy conditions imposed by the ptrace
interface on 64 bit architectures. There have been reproducible reports
of that not always being the case:
facebookexperimental/hermit#41. Use an
explicitly aligned data structure to enforce this.

Signed-off-by: Bjoern Doebel <[email protected]>

reverie-ptrace/src/vdso.rs

@@ -27,35 +27,48 @@ use tracing::debug;
 mod vdso_syms {
     #![allow(non_upper_case_globals)]
 
-    pub const time: &[u8; 8] = &[
+    #[repr(align(64))]
+    struct CodeAligned([u8;8]);
+
+    const time_code: CodeAligned = CodeAligned([
         0xb8, 0xc9, 0x00, 0x00, 0x00, // mov %SYS_time, %eax
         0x0f, 0x05, // syscall
         0xc3, // retq
-    ];
+    ]);
+
+    pub const time: &[u8; 8] = &time_code.0;
 
-    pub const clock_gettime: &[u8; 8] = &[
+    const clock_gettime_code: CodeAligned = CodeAligned([
         0xb8, 0xe4, 0x00, 0x00, 0x00, // mov SYS_clock_gettime, %eax
         0x0f, 0x05, // syscall
         0xc3, // retq
-    ];
+    ]);
+
+    pub const clock_gettime: &[u8; 8] = &clock_gettime_code.0;
 
-    pub const getcpu: &[u8; 8] = &[
+    const getcpu_code: CodeAligned = CodeAligned([
         0xb8, 0x35, 0x01, 0x00, 0x00, // mov SYS_getcpu, %eax
         0x0f, 0x05, // syscall
         0xc3, // retq
-    ];
+    ]);
 
-    pub const gettimeofday: &[u8; 8] = &[
+    pub const getcpu: &[u8; 8] = &getcpu_code.0;
+
+    const gettimeofday_code: CodeAligned = CodeAligned([
         0xb8, 0x60, 0x00, 0x00, 0x00, // mov SYS_gettimeofday, %eax
         0x0f, 0x05, // syscall
         0xc3, // retq
-    ];
+    ]);
+
+    pub const gettimeofday: &[u8; 8] = &gettimeofday_code.0;
 
-    pub const clock_getres: &[u8; 8] = &[
+    const clock_getres_code: CodeAligned = CodeAligned([
         0xb8, 0xe5, 0x00, 0x00, 0x00, // mov SYS_clock_getres, %eax
         0x0f, 0x05, // syscall
         0xc3, // retq
-    ];
+    ]);
+
+    pub const clock_getres: &[u8; 8] = &clock_getres_code.0;
 }
 
 #[cfg(target_arch = "aarch64")]