Add more comments and make the src/arch/* files more consistent. (#43)

Author: sunfishcode

src/arch/aarch64.rs

@@ -50,20 +50,26 @@ pub(super) unsafe fn clone(
 }
 
 /// Write a value to the platform thread-pointer register.
-#[cfg(feature = "origin-thread")]
+#[cfg(all(
+    feature = "origin-thread",
+    any(feature = "origin-start", feature = "external-start")
+))]
 #[inline]
 pub(super) unsafe fn set_thread_pointer(ptr: *mut c_void) {
-    asm!("msr tpidr_el0,{0}", in(reg) ptr);
+    asm!("msr tpidr_el0,{}", in(reg) ptr);
     debug_assert_eq!(get_thread_pointer(), ptr);
 }
 
 /// Read the value of the platform thread-pointer register.
-#[cfg(feature = "origin-thread")]
+#[cfg(all(
+    feature = "origin-thread",
+    any(feature = "origin-start", feature = "external-start")
+))]
 #[inline]
 pub(super) fn get_thread_pointer() -> *mut c_void {
     let ptr;
     unsafe {
-        asm!("mrs {0},tpidr_el0", out(reg) ptr, options(nostack, preserves_flags, readonly));
+        asm!("mrs {},tpidr_el0", out(reg) ptr, options(nostack, preserves_flags, readonly));
     }
     ptr
 }

src/arch/arm.rs

@@ -51,20 +51,26 @@ pub(super) unsafe fn clone(
 }
 
 /// Write a value to the platform thread-pointer register.
-#[cfg(feature = "origin-thread")]
+#[cfg(all(
+    feature = "origin-thread",
+    any(feature = "origin-start", feature = "external-start")
+))]
 #[inline]
 pub(super) unsafe fn set_thread_pointer(ptr: *mut c_void) {
     rustix::runtime::arm_set_tls(ptr).expect("arm_set_tls");
     debug_assert_eq!(get_thread_pointer(), ptr);
 }
 
 /// Read the value of the platform thread-pointer register.
-#[cfg(feature = "origin-thread")]
+#[cfg(all(
+    feature = "origin-thread",
+    any(feature = "origin-start", feature = "external-start")
+))]
 #[inline]
 pub(super) fn get_thread_pointer() -> *mut c_void {
     let ptr;
     unsafe {
-        asm!("mrc p15,0,{0},c13,c0,3", out(reg) ptr);
+        asm!("mrc p15,0,{},c13,c0,3", out(reg) ptr);
     }
     ptr
 }

src/arch/riscv64.rs

@@ -47,20 +47,26 @@ pub(super) unsafe fn clone(
 }
 
 /// Write a value to the platform thread-pointer register.
-#[cfg(feature = "origin-thread")]
+#[cfg(all(
+    feature = "origin-thread",
+    any(feature = "origin-start", feature = "external-start")
+))]
 #[inline]
 pub(super) unsafe fn set_thread_pointer(ptr: *mut c_void) {
-    asm!("mv tp,{0}", in(reg) ptr);
+    asm!("mv tp,{}", in(reg) ptr);
     debug_assert_eq!(get_thread_pointer(), ptr);
 }
 
 /// Read the value of the platform thread-pointer register.
-#[cfg(feature = "origin-thread")]
+#[cfg(all(
+    feature = "origin-thread",
+    any(feature = "origin-start", feature = "external-start")
+))]
 #[inline]
 pub(super) fn get_thread_pointer() -> *mut c_void {
     let ptr;
     unsafe {
-        asm!("mv {0},tp", out(reg) ptr, options(nostack, preserves_flags, readonly));
+        asm!("mv {},tp", out(reg) ptr, options(nostack, preserves_flags, readonly));
     }
     ptr
 }

src/arch/x86.rs

@@ -89,7 +89,10 @@ pub(super) unsafe fn clone(
 }
 
 /// Write a value to the platform thread-pointer register.
-#[cfg(feature = "origin-thread")]
+#[cfg(all(
+    feature = "origin-thread",
+    any(feature = "origin-start", feature = "external-start")
+))]
 #[inline]
 pub(super) unsafe fn set_thread_pointer(ptr: *mut c_void) {
     let mut user_desc = rustix::runtime::UserDesc {
@@ -113,12 +116,15 @@ pub(super) unsafe fn set_thread_pointer(ptr: *mut c_void) {
 }
 
 /// Read the value of the platform thread-pointer register.
-#[cfg(feature = "origin-thread")]
+#[cfg(all(
+    feature = "origin-thread",
+    any(feature = "origin-start", feature = "external-start")
+))]
 #[inline]
 pub(super) fn get_thread_pointer() -> *mut c_void {
     let ptr;
     unsafe {
-        asm!("mov {0},DWORD PTR gs:0", out(reg) ptr, options(nostack, preserves_flags, readonly));
+        asm!("mov {},DWORD PTR gs:0", out(reg) ptr, options(nostack, preserves_flags, readonly));
     }
     ptr
 }

src/lib.rs

@@ -100,9 +100,9 @@ unsafe extern "C" fn _start() -> ! {
     #[cfg(target_arch = "x86")]
     asm!(
         "mov eax, esp", // Save the incoming `esp` value.
-        "push ebp",     // Pad for alignment.
-        "push ebp",     // Pad for alignment.
-        "push ebp",     // Pad for alignment.
+        "push ebp",     // Pad for stack pointer alignment.
+        "push ebp",     // Pad for stack pointer alignment.
+        "push ebp",     // Pad for stack pointer alignment.
         "push eax",     // Pass saved the incoming `esp` as the arg to `entry`.
         "push ebp",     // Set the return address to zero.
         "jmp {entry}",  // Jump to `entry`.