Merge of #704: Add cygwin support

There is no `OsString::from_wide` on Cygwin because Cygwin is a "Unix"
so use Cygwin APIs for the conversion.

* Add cygwin support
* Use correct name buffer size
* Convert path to posix
* Update libc to 0.2.171 to meet cygwin's requirement
* Use mystd instead of std
* Add docs for `cygwin_conv_path`
* Adjust signature of `cygwin_conv_path`
* Fix windows-targets dep in as-if-std
* Use `Vec::with_capacity` to alloc buffer
* Update safety comments

Author: workingjubilee

Cargo.lock

@@ -38,7 +38,7 @@ cpp_demangle = { default-features = false, version = "0.4.0", optional = true, f
   "alloc",
 ] }
 
-[target.'cfg(windows)'.dependencies]
+[target.'cfg(any(windows, target_os = "cygwin"))'.dependencies]
 windows-targets = "0.52.6"
 
 [target.'cfg(not(all(windows, target_env = "msvc", not(target_vendor = "uwp"))))'.dependencies]

Cargo.toml

@@ -27,7 +27,7 @@ default-features = false
 optional = true
 features = ['read_core', 'elf', 'macho', 'pe', 'xcoff', 'unaligned', 'archive']
 
-[target.'cfg(windows)'.dependencies]
+[target.'cfg(any(windows, target_os = "cygwin"))'.dependencies]
 windows-targets = "0.52.6"
 
 [features]

crates/as-if-std/Cargo.toml

@@ -247,5 +247,5 @@ mod lock {
 ))]
 mod dbghelp;
 // Auto-generated by windows-bindgen/riddle
-#[cfg(windows)]
+#[cfg(any(windows, target_os = "cygwin"))]
 mod windows_sys;

src/lib.rs

@@ -43,6 +43,7 @@ cfg_if::cfg_if! {
         target_os = "solaris",
         target_os = "illumos",
         target_os = "aix",
+        target_os = "cygwin",
     ))] {
         #[path = "gimli/mmap_unix.rs"]
         mod mmap;
@@ -193,7 +194,7 @@ fn mmap(path: &Path) -> Option<Mmap> {
 }
 
 cfg_if::cfg_if! {
-    if #[cfg(windows)] {
+    if #[cfg(any(windows, target_os = "cygwin"))] {
         mod coff;
         use self::coff::{handle_split_dwarf, Object};
     } else if #[cfg(any(target_vendor = "apple"))] {
@@ -209,7 +210,7 @@ cfg_if::cfg_if! {
 }
 
 cfg_if::cfg_if! {
-    if #[cfg(windows)] {
+    if #[cfg(any(windows, target_os = "cygwin"))] {
         mod libs_windows;
         use libs_windows::native_libraries;
     } else if #[cfg(target_vendor = "apple")] {

src/symbolize/gimli.rs

@@ -1,6 +1,5 @@
 use super::super::super::windows_sys::*;
 use super::mystd::ffi::OsString;
-use super::mystd::os::windows::prelude::*;
 use super::{coff, mmap, Library, LibrarySegment};
 use alloc::vec;
 use alloc::vec::Vec;
@@ -43,13 +42,79 @@ unsafe fn add_loaded_images(ret: &mut Vec<Library>) {
     }
 }
 
+// Safety: long_path should be null-terminated
+#[cfg(target_os = "cygwin")]
+unsafe fn get_posix_path(long_path: &[u16]) -> Option<OsString> {
+    use super::mystd::os::unix::ffi::OsStringExt;
+
+    unsafe extern "C" {
+        // Doc: https://cygwin.com/cygwin-api/func-cygwin-conv-path.html
+        // Src: https://github.com/cygwin/cygwin/blob/718a15ba50e0d01c79800bd658c2477f9a603540/winsup/cygwin/path.cc#L3902
+        // Safety:
+        // * `what` should be `CCP_WIN_W_TO_POSIX` here
+        // * `from` is null-terminated UTF-16 path
+        // * `to` is buffer, the buffer size is `size`.
+        fn cygwin_conv_path(
+            what: libc::c_uint,
+            from: *const u16,
+            to: *mut u8,
+            size: libc::size_t,
+        ) -> libc::ssize_t;
+    }
+    const CCP_WIN_W_TO_POSIX: libc::c_uint = 3;
+
+    // If `size` is 0, returns needed buffer size, including null terminator;
+    // or -1 if error.
+    // Safety: if `size` is 0, `to` is not used.
+    let name_len = unsafe {
+        cygwin_conv_path(
+            CCP_WIN_W_TO_POSIX,
+            long_path.as_ptr(),
+            core::ptr::null_mut(),
+            0,
+        )
+    };
+    // Expect at least 1 for null terminator.
+    // It's not likely to return error here.
+    if name_len < 1 {
+        return None;
+    }
+    let name_len = name_len as usize;
+    let mut name_buffer = Vec::with_capacity(name_len);
+    // Safety: `name_buffer` is large enough.
+    let res = unsafe {
+        cygwin_conv_path(
+            CCP_WIN_W_TO_POSIX,
+            long_path.as_ptr(),
+            name_buffer.as_mut_ptr(),
+            name_len,
+        )
+    };
+    // It's not likely to return error here.
+    if res != 0 {
+        return None;
+    }
+    // Remove the null terminator.
+    unsafe { name_buffer.set_len(name_len - 1) };
+    let name = OsString::from_vec(name_buffer);
+    Some(name)
+}
+
 unsafe fn load_library(me: &MODULEENTRY32W) -> Option<Library> {
-    let pos = me
-        .szExePath
-        .iter()
-        .position(|i| *i == 0)
-        .unwrap_or(me.szExePath.len());
-    let name = OsString::from_wide(&me.szExePath[..pos]);
+    #[cfg(windows)]
+    let name = {
+        use super::mystd::os::windows::prelude::*;
+        let pos = me
+            .szExePath
+            .iter()
+            .position(|i| *i == 0)
+            .unwrap_or(me.szExePath.len());
+        OsString::from_wide(&me.szExePath[..pos])
+    };
+    #[cfg(target_os = "cygwin")]
+    // Safety: the path with max length MAX_PATH always contains a null
+    // terminator. Don't slice it.
+    let name = unsafe { get_posix_path(&me.szExePath[..])? };
 
     // MinGW libraries currently don't support ASLR
     // (rust-lang/rust#16514), but DLLs can still be relocated around in