From b992e37559221faba58abef5e3662ef2a1b4b4ea Mon Sep 17 00:00:00 2001
From: Dan Gohman <dev@sunfishcode.online>
Date: Sat, 9 Sep 2023 12:22:17 -0700
Subject: [PATCH] Add more comments and make the src/arch/* files more
 consistent.

---
 src/arch/aarch64.rs | 14 ++++++++++----
 src/arch/arm.rs     | 12 +++++++++---
 src/arch/riscv64.rs | 14 ++++++++++----
 src/arch/x86.rs     | 12 +++++++++---
 src/lib.rs          |  6 +++---
 5 files changed, 41 insertions(+), 17 deletions(-)

diff --git a/src/arch/aarch64.rs b/src/arch/aarch64.rs
index c9f38a5..97d3b95 100644
--- a/src/arch/aarch64.rs
+++ b/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
 }
diff --git a/src/arch/arm.rs b/src/arch/arm.rs
index e41963b..3f972e4 100644
--- a/src/arch/arm.rs
+++ b/src/arch/arm.rs
@@ -51,7 +51,10 @@ 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) {
     rustix::runtime::arm_set_tls(ptr).expect("arm_set_tls");
@@ -59,12 +62,15 @@ 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!("mrc p15,0,{0},c13,c0,3", out(reg) ptr);
+        asm!("mrc p15,0,{},c13,c0,3", out(reg) ptr);
     }
     ptr
 }
diff --git a/src/arch/riscv64.rs b/src/arch/riscv64.rs
index d1118f3..8dbbd0a 100644
--- a/src/arch/riscv64.rs
+++ b/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
 }
diff --git a/src/arch/x86.rs b/src/arch/x86.rs
index 99acec8..03876bf 100644
--- a/src/arch/x86.rs
+++ b/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
 }
diff --git a/src/lib.rs b/src/lib.rs
index c465394..62f1b5a 100644
--- a/src/lib.rs
+++ b/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`.