docs: doc that signal-unsafe fns can be called after execve

Author: SteveLauC

src/pty.rs

@@ -334,9 +334,9 @@ feature! {
 /// # Safety
 ///
 /// In a multithreaded program, only [async-signal-safe] functions like `pause`
-/// and `_exit` may be called by the child (the parent isn't restricted). Note
-/// that memory allocation may **not** be async-signal-safe and thus must be
-/// prevented.
+/// and `_exit` may be called by the child (the parent isn't restricted) until
+/// a call of `execve(2)`. Note that memory allocation may **not** be 
+/// async-signal-safe and thus must be prevented.
 ///
 /// Those functions are only a small subset of your operating system's API, so
 /// special care must be taken to only invoke code you can control and audit.

src/unistd.rs

@@ -265,9 +265,9 @@ impl ForkResult {
 /// # Safety
 ///
 /// In a multithreaded program, only [async-signal-safe] functions like `pause`
-/// and `_exit` may be called by the child (the parent isn't restricted). Note
-/// that memory allocation may **not** be async-signal-safe and thus must be
-/// prevented.
+/// and `_exit` may be called by the child (the parent isn't restricted) until
+/// a call of `execve(2)`. Note that memory allocation may **not** be
+/// async-signal-safe and thus must be prevented.
 ///
 /// Those functions are only a small subset of your operating system's API, so
 /// special care must be taken to only invoke code you can control and audit.