std crate builds with stubs

.gitignore

@@ -4,6 +4,8 @@
 # download cosmo amalgamation
 /libcosmo/*
 !/libcosmo/README.md
+!/libcosmo/compile-stubs.bash
+!/libcosmo/stubs.c
 
 # Generated by Cargo
 # will have compiled files and executables

README.md

@@ -51,63 +51,21 @@ objcopy -SO binary ./target/x86_64-unknown-linux-cosmo/debug/hello_world.com.dbg
 
 ## What about the `std` crate?
 
-The `std` crate compiles successfully, but fails at the linker stage. Here's how
+1. It needs a few stubs functions so the linker doesn't complain. I wrote them
-that can be tested:
+   out in `stubs.c`.
 
-1. Change the source code in `src/main.rs` to use the commented out `main`
+```bash
-   function and `#![restricted_std]`.
+cd ./libcosmo/
-
+# compiling a simple stub file via cosmopolitan.h
-2. In the source code for Rust's `std` crate, change a `cfg_if` in
+./compile-stubs.bash
-   `$HOME/.rustup/toolchains/<your-host-nightly-toolchain>/lib/rustlib/src/rust/library/backtrace/src/backtrace/mod.rs`
-   to use the `noop` trace instead of depending on `libunwind`. 
-
-```diff
---- mod.rs	2022-06-21 12:52:21.724053459 +0530
-+++ mod.rs	2022-06-21 13:05:50.948777093 +0530
-@@ -132,7 +132,7 @@
-         pub(crate) mod miri;
-         use self::miri::trace as trace_imp;
-         pub(crate) use self::miri::Frame as FrameImp;
--    } else if #[cfg(
-+    } /* else if #[cfg(
-         any(
-             all(
-                 unix,
-@@ -154,7 +154,7 @@
-         pub(crate) use self::dbghelp::Frame as FrameImp;
-         #[cfg(target_env = "msvc")] // only used in dbghelp symbolize
-         pub(crate) use self::dbghelp::StackFrame;
--    } else {
-+    } */ else {
-         mod noop;
-         use self::noop::trace as trace_imp;
-         pub(crate) use self::noop::Frame as FrameImp;
 ```
 
-I haven't figured out what config I should give to `cargo` so I don't need to do
+2. The build command now changes to
-this. I find it surprising that `std` cannot be built without relying on
-`libunwind`.
-
-3. The build command now changes to
 
 ```bash
 cargo +nightly build -Zbuild-std=core,alloc,panic_abort,libc,std -Zbuild-std-features=  --target=./x86_64-unknown-linux-cosmo.json
 ```
 
-4. At the linker stage you might find some of the following symbols are missing:
-  
-  - If `Unwind_Backtrace` or similar is missing, you need to check if step 2 is
-    done properly.
-
-  - `open64`, `stat64`, `fstat64`, `__xpg_strerror_r`: these can be added to
-    Cosmopolitan Libc via aliases of the existing functions.
-
-  - `pthread_key_create`,`pthread_setspecific`,`pthread_key_delete`,`pthread_getspecific`
-    -- these functions should not be needed in a single-threaded program, but
-    somehow they are still linked. Support for threads is currently being added
-    to Cosmopolitan Libc, but possibly the related code in the `std` crate can
-    be changed to avoid this issue.
-
 [rust]: https://rust-lang.org
 [cosmo]: https://github.com/jart/cosmopolitan
 [amalg-download]: https://justine.lol/cosmopolitan/download.html

libcosmo/compile-stubs.bash

@@ -0,0 +1,7 @@
+#!/usr/bin/env bash
+set -eux
+
+gcc -g -Os -static -nostdlib -nostdinc \
+  -fno-pie -no-pie -mno-red-zone \
+  -fno-omit-frame-pointer -pg -mnop-mcount \
+  -o ./stubs.o -c ./stubs.c

libcosmo/stubs.c

@@ -0,0 +1,98 @@
+#include "cosmopolitan.h"
+
+typedef enum {
+  _URC_NO_REASON = 0,
+  _URC_FOREIGN_EXCEPTION_CAUGHT = 1,
+  _URC_FATAL_PHASE2_ERROR = 2,
+  _URC_FATAL_PHASE1_ERROR = 3,
+  _URC_NORMAL_STOP = 4,
+  _URC_END_OF_STACK = 5,
+  _URC_HANDLER_FOUND = 6,
+  _URC_INSTALL_CONTEXT = 7,
+  _URC_CONTINUE_UNWIND = 8
+} _Unwind_Reason_Code;
+
+#define UNW_TDEP_CURSOR_LEN 127
+
+typedef uint64_t unw_word_t;
+
+typedef struct unw_cursor {
+  unw_word_t opaque[UNW_TDEP_CURSOR_LEN];
+} unw_cursor_t;
+
+struct _Unwind_Context {
+  unw_cursor_t cursor;
+  int end_of_stack;
+};
+
+typedef _Unwind_Reason_Code (*_Unwind_Trace_Fn)(struct _Unwind_Context *,
+                                                void *);
+
+uintptr_t _Unwind_GetCFA(struct _Unwind_Context *ctx) {
+  return 0;
+}
+
+uintptr_t _Unwind_GetIP(struct _Unwind_Context *ctx) {
+  return 0;
+}
+
+_Unwind_Reason_Code _Unwind_Backtrace(_Unwind_Trace_Fn fn, void *arg) {
+  return _URC_NORMAL_STOP;
+}
+
+void *_Unwind_FindEnclosingFunction(void *arg) {
+  return NULL;
+}
+
+#define MAX_KEYS 64
+
+typedef unsigned pthread_key_t;
+typedef void (*dtor)(void*);
+
+typedef struct {
+    pthread_key_t kval;
+    dtor d;
+    void *value;
+} tls_t;
+
+static tls_t my_tls[MAX_KEYS] = {0};
+static unsigned thread_avail = 0;
+
+int pthread_key_create(pthread_key_t *k, dtor destructor) {
+    for(pthread_key_t i=1; i<MAX_KEYS; i++) {
+        if(my_tls[i].kval == 0) {
+               *k = i;
+               my_tls[i].kval = i;
+               my_tls[i].d = destructor;
+               return 0;
+        }
+    }
+    return -1;
+}
+
+void* pthread_getspecific(pthread_key_t k) {
+    if(k < MAX_KEYS) {
+        return my_tls[k].value;
+    }
+    return NULL;
+}
+
+int pthread_setspecific(pthread_key_t k, const void* value) {
+    if(k < MAX_KEYS) {
+        my_tls[k].value = value;
+        return 0;
+    }
+    return -1;
+}
+
+int pthread_key_delete(pthread_key_t k) {
+    if (k < MAX_KEYS) {
+        my_tls[k].kval = 0;
+        return 0;
+    }
+    return -1;
+}
+
+int __xpg_strerror_r(int a, char *b, size_t c) {
+    return strerror_r(a, b, c);
+}

src/main.rs

@@ -1,3 +1,4 @@
+/*
 #![no_main]
 #![no_std]
 #![feature(rustc_private)]
@@ -20,12 +21,10 @@ pub extern "C" fn main(_argc: isize, _argv: *const *const u8) -> isize {
 fn my_panic(_info: &core::panic::PanicInfo) -> ! {
     loop {}
 }
-
+*/
-/* std crate requires some external changes
 
 #![feature(restricted_std)]
 
 pub fn main() {
     println!("hello pls cosmo rust APE");
 }
-*/

x86_64-unknown-linux-cosmo.json

@@ -49,6 +49,7 @@
           "-fuse-ld=bfd",
           "-Wl,-T,./libcosmo/ape.lds",
           "./libcosmo/crt.o",
+          "./libcosmo/stubs.o",
           "./libcosmo/ape-no-modify-self.o",
           "./libcosmo/cosmopolitan.a"
       ]