update platform-support.md

Author: nyurik

library/std/src/sys/pal/unix/process/process_unix.rs

@@ -24,7 +24,8 @@ use libc::{c_int, pid_t};
 use libc::{gid_t, uid_t};
 
 cfg_if::cfg_if! {
-    if #[cfg(target_os = "nto")] {
+    // This workaround is only needed for QNX 7.0 and 7.1. The bug should have been fixed in 8.0
+    if #[cfg(any(target_env = "nto70", target_env = "nto71"))] {
         use crate::thread;
         use libc::{c_char, posix_spawn_file_actions_t, posix_spawnattr_t};
         use crate::time::Duration;
@@ -191,7 +192,12 @@ impl Command {
 
     // Attempts to fork the process. If successful, returns Ok((0, -1))
     // in the child, and Ok((child_pid, -1)) in the parent.
-    #[cfg(not(any(target_os = "watchos", target_os = "tvos", target_os = "nto")))]
+    #[cfg(not(any(
+        target_os = "watchos",
+        target_os = "tvos",
+        target_env = "nto70",
+        target_env = "nto71"
+    )))]
     unsafe fn do_fork(&mut self) -> Result<pid_t, io::Error> {
         cvt(libc::fork())
     }
@@ -200,7 +206,8 @@ impl Command {
     // or closed a file descriptor while the fork() was occurring".
     // Documentation says "... or try calling fork() again". This is what we do here.
     // See also https://www.qnx.com/developers/docs/7.1/#com.qnx.doc.neutrino.lib_ref/topic/f/fork.html
-    #[cfg(target_os = "nto")]
+    // This workaround is only needed for QNX 7.0 and 7.1. The bug should have been fixed in 8.0
+    #[cfg(any(target_env = "nto70", target_env = "nto71"))]
     unsafe fn do_fork(&mut self) -> Result<pid_t, io::Error> {
         use crate::sys::os::errno;
 

src/doc/rustc/src/platform-support.md

@@ -254,6 +254,7 @@ target | std | host | notes
 [`aarch64-kmc-solid_asp3`](platform-support/kmc-solid.md) | ✓ |  | ARM64 SOLID with TOPPERS/ASP3
 [`aarch64-nintendo-switch-freestanding`](platform-support/aarch64-nintendo-switch-freestanding.md) | * |  | ARM64 Nintendo Switch, Horizon
 [`aarch64-unknown-teeos`](platform-support/aarch64-unknown-teeos.md) | ? |  | ARM64 TEEOS |
+[`aarch64-unknown-nto-qnx700`](platform-support/nto-qnx.md) | ? |  | ARM64 QNX Neutrino 7.0 RTOS |
 [`aarch64-unknown-nto-qnx710`](platform-support/nto-qnx.md) | ✓ |  | ARM64 QNX Neutrino 7.1 RTOS |
 `aarch64-unknown-freebsd` | ✓ | ✓ | ARM64 FreeBSD
 [`aarch64-unknown-hermit`](platform-support/hermit.md) | ✓ |  | ARM64 Hermit

src/doc/rustc/src/platform-support/nto-qnx.md

@@ -24,6 +24,7 @@ Currently, the following QNX Neutrino versions and compilation targets are suppo
 |----------------------|---------------------|:------------:|:----------------:|
 | 7.1 | AArch64 | ✓ | ✓ |
 | 7.1 | x86_64  | ✓ | ✓ |
+| 7.0 | AArch64 | ? | ✓ |
 | 7.0 | x86     |   | ✓ |
 
 Adding other architectures that are supported by QNX Neutrino is possible.
@@ -43,6 +44,23 @@ When linking `no_std` applications, they must link against `libc.so` (see exampl
 required because applications always link against the `crt` library and `crt` depends on `libc.so`.
 This is done automatically when using the standard library.
 
+### Disabling RELocation Read-Only (RELRO)
+
+While not recommended by default, some QNX kernel setups may require the `RELRO` to be disabled with `-C relro_level=off`, e.g. by adding it to the `.cargo/config.toml` file:
+
+```toml
+[target.aarch64-unknown-nto-qnx700]
+rustflags = ["-C", "relro_level=off"]
+```
+
+If your QNX kernel does not allow it, and `relro` is not disabled, running compiled binary would fail with `syntax error: ... unexpected` or similar.  This is due to kernel trying to interpret compiled binary with `/bin/sh`, and obviously failing.  To verify that this is really the case, run your binary with the `DL_DEBUG=all` env var, and look for this output. If you see it, you should disable `relro` as described above.
+
+```text
+Resolution scope for Executable->/bin/sh:
+        Executable->/bin/sh
+        libc.so.4->/usr/lib/ldqnx-64.so.2
+```
+
 ### Small example application
 
 Small `no_std` example is shown below. Applications using the standard library work as well.