std now builds with latest nightly of cosmo

README.md

@@ -13,7 +13,10 @@ use `rustc` or equivalent compiler to generate `.o` files, and then write a
 shell script that does the linking with the expected flags. I have not tried
 this method.
 
-## Build steps
+> a previous attempt at a Rust APE was done without using the `std` crate. You
+can view that in the [`without-std` branch of this repo][without-std-branch].
+
+## Building a Rust APE with the `std` crate
 
 1. Download the Cosmopolitan Libc [amalgamation][amalg-download] into the `libcosmo` folder:
 
@@ -24,10 +27,13 @@ unzip cosmopolitan.zip
 cd ../
 ```
 
-2. Download the necessary *host* toolchain and source code for Rust:
+For reference, I used the nightly version of `cosmopolitan.a` from June 22 2022,
+which can be built from source if needed from [this commit][cosmo-nightly].
+
+2. Download the necessary host toolchain and source code for Rust:
 
 ```bash
-# I was on Debian, so I did this
+# I was on Debian 11, so I did this
 rustup toolchain install nightly-x86_64-unknown-linux-gnu
 rustup component add rust-src --toolchain nightly-x86_64-unknown-linux-gnu
 # on Alpine Linux, you may need to do
@@ -35,39 +41,71 @@ rustup toolchain install nightly-x86_64-unknown-linux-musl
 rustup component add rust-src --toolchain nightly-x86_64-unknown-linux-musl
 ```
 
+For reference, I used the nightly version of Rust from June 22 2022.
+
 3. run `cargo build` to get the debug executable. This uses a bash script that
    removes unnecessary linker arguments. A recent version of `gcc` and `ld.bfd`
    is required.
 
 ```bash
-cargo +nightly build -Zbuild-std=core,libc --target=./x86_64-unknown-linux-cosmo.json
+cargo +nightly build -Zbuild-std=panic_abort,std -Zbuild-std-features=""  --target=./x86_64-unknown-linux-cosmo.json
+```
+
+For reference, I used the below versions of `gcc` and `ld.bfd`
+
+```
+gcc (Debian 10.2.1-6) 10.2.1 20210110
+Copyright (C) 2020 Free Software Foundation, Inc.
+This is free software; see the source for copying conditions.  There is NO
+warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+```
+
+```
+GNU ld (GNU Binutils for Debian) 2.35.2
+Copyright (C) 2020 Free Software Foundation, Inc.
+This program is free software; you may redistribute it under the terms of
+the GNU General Public License version 3 or (at your option) a later version.
+This program has absolutely no warranty.
 ```
 
 4. run `objcopy` on the debug binary to obtain the APE:
 
 ```bash
+# objcopy is the same version as ld.bfd above
 objcopy -SO binary ./target/x86_64-unknown-linux-cosmo/debug/hello_world.com.dbg ./hello_world.com
+# run the APE
+./hello_world.com
+# see syscalls made by the APE
+./hello_world.com --strace
 ```
 
-## What about the `std` crate?
+Now we have an Actually Portable Executable built with Rust! There might some
+edge cases that I haven't noticed, so clone/fork the repo and try it out!  The
+[`without-std` branch][without-std-branch] of this repo might be useful.
 
-1. It needs a few stubs functions so the linker doesn't complain. I wrote them
-   out in `stubs.c`.
+## TODOs
 
-```bash
-cd ./libcosmo/
-# compiling a simple stub file via cosmopolitan.h
-./compile-stubs.bash
-```
+- [ ] figure out build config to avoid using `libunwind`
 
-2. The build command now changes to
+The `std` crate relies on
+[`backtrace`](https://github.com/rust-lang/backtrace-rs), which depends on
+[`libunwind`](https://github.com/libunwind/libunwind) in the default builds for
+unix. To work around this, `cosmopolitan.a` currently has stubs for the
+functions that `backtrace` relies on. However, it might be easier to provide a
+build flag in `Cargo.toml` to use the `noop` module of `backtrace`. 
 
-```bash
-cargo +nightly build -Zbuild-std=core,alloc,panic_abort,libc,std -Zbuild-std-features=  --target=./x86_64-unknown-linux-cosmo.json
-```
+A small change needs to be submitted to the source code of `backtrace` (in the
+`cfg_if!`
+[here](https://github.com/rust-lang/backtrace-rs/blob/4e5a3f72929f152752d5659e95bb15c8f6b41eff/src/backtrace/mod.rs#L128))
+to allow choosing `noop` when building as part of the `std` crate. This
+conditional compilation flag should be accessible when building the `std` crate
+either via `Cargo.toml` or something like `-Z use-std-backtrace-noop` in the
+build command.
 
+[without-std-branch]: https://github.com/ahgamut/rust-ape-example/tree/without-std
 [rust]: https://rust-lang.org
 [cosmo]: https://github.com/jart/cosmopolitan
+[cosmo-nightly]: https://github.com/jart/cosmopolitan
 [amalg-download]: https://justine.lol/cosmopolitan/download.html
 [custom-target]: https://doc.rust-lang.org/rustc/targets/custom.html
 [custom-embed]: https://docs.rust-embedded.org/embedonomicon/custom-target.html

libcosmo/compile-stubs.bash

@@ -1,7 +0,0 @@
-#!/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

@@ -1,98 +0,0 @@
-#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

@@ -26,5 +26,5 @@ fn my_panic(_info: &core::panic::PanicInfo) -> ! {
 #![feature(restricted_std)]
 
 pub fn main() {
-    println!("hello pls cosmo rust APE");
+    println!("Hello World! This is an APE built with Rust.");
 }

x86_64-unknown-linux-cosmo.json

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