rustc_codegen_ssa/back/
command.rs

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1//! A thin wrapper around `Command` in the standard library which allows us to
2//! read the arguments that are built up.
3
4use std::ffi::{OsStr, OsString};
5use std::process::{self, Output};
6use std::{fmt, io, mem};
7
8use rustc_target::spec::LldFlavor;
9
10#[derive(Clone)]
11pub(crate) struct Command {
12    program: Program,
13    args: Vec<OsString>,
14    env: Vec<(OsString, OsString)>,
15    env_remove: Vec<OsString>,
16    env_clear: bool,
17}
18
19#[derive(Clone)]
20enum Program {
21    Normal(OsString),
22    CmdBatScript(OsString),
23    Lld(OsString, LldFlavor),
24}
25
26impl Command {
27    pub(crate) fn new<P: AsRef<OsStr>>(program: P) -> Command {
28        Command::_new(Program::Normal(program.as_ref().to_owned()))
29    }
30
31    pub(crate) fn bat_script<P: AsRef<OsStr>>(program: P) -> Command {
32        Command::_new(Program::CmdBatScript(program.as_ref().to_owned()))
33    }
34
35    pub(crate) fn lld<P: AsRef<OsStr>>(program: P, flavor: LldFlavor) -> Command {
36        Command::_new(Program::Lld(program.as_ref().to_owned(), flavor))
37    }
38
39    fn _new(program: Program) -> Command {
40        Command {
41            program,
42            args: Vec::new(),
43            env: Vec::new(),
44            env_remove: Vec::new(),
45            env_clear: false,
46        }
47    }
48
49    pub(crate) fn arg<P: AsRef<OsStr>>(&mut self, arg: P) -> &mut Command {
50        self._arg(arg.as_ref());
51        self
52    }
53
54    pub(crate) fn args<I>(&mut self, args: I) -> &mut Command
55    where
56        I: IntoIterator<Item: AsRef<OsStr>>,
57    {
58        for arg in args {
59            self._arg(arg.as_ref());
60        }
61        self
62    }
63
64    fn _arg(&mut self, arg: &OsStr) {
65        self.args.push(arg.to_owned());
66    }
67
68    pub(crate) fn env<K, V>(&mut self, key: K, value: V) -> &mut Command
69    where
70        K: AsRef<OsStr>,
71        V: AsRef<OsStr>,
72    {
73        self._env(key.as_ref(), value.as_ref());
74        self
75    }
76
77    fn _env(&mut self, key: &OsStr, value: &OsStr) {
78        self.env.push((key.to_owned(), value.to_owned()));
79    }
80
81    pub(crate) fn env_remove<K>(&mut self, key: K) -> &mut Command
82    where
83        K: AsRef<OsStr>,
84    {
85        self._env_remove(key.as_ref());
86        self
87    }
88
89    pub(crate) fn env_clear(&mut self) -> &mut Command {
90        self.env_clear = true;
91        self
92    }
93
94    fn _env_remove(&mut self, key: &OsStr) {
95        self.env_remove.push(key.to_owned());
96    }
97
98    pub(crate) fn output(&mut self) -> io::Result<Output> {
99        self.command().output()
100    }
101
102    pub(crate) fn command(&self) -> process::Command {
103        let mut ret = match self.program {
104            Program::Normal(ref p) => process::Command::new(p),
105            Program::CmdBatScript(ref p) => {
106                let mut c = process::Command::new("cmd");
107                c.arg("/c").arg(p);
108                c
109            }
110            Program::Lld(ref p, flavor) => {
111                let mut c = process::Command::new(p);
112                c.arg("-flavor").arg(flavor.as_str());
113                c
114            }
115        };
116        ret.args(&self.args);
117        ret.envs(self.env.clone());
118        for k in &self.env_remove {
119            ret.env_remove(k);
120        }
121        if self.env_clear {
122            ret.env_clear();
123        }
124        ret
125    }
126
127    // extensions
128
129    pub(crate) fn get_args(&self) -> &[OsString] {
130        &self.args
131    }
132
133    pub(crate) fn take_args(&mut self) -> Vec<OsString> {
134        mem::take(&mut self.args)
135    }
136
137    /// Returns a `true` if we're pretty sure that this'll blow OS spawn limits,
138    /// or `false` if we should attempt to spawn and see what the OS says.
139    pub(crate) fn very_likely_to_exceed_some_spawn_limit(&self) -> bool {
140        #[cfg(not(any(windows, unix)))]
141        {
142            return false;
143        }
144
145        // On Unix the limits can be gargantuan anyway so we're pretty
146        // unlikely to hit them, but might still exceed it.
147        // We consult ARG_MAX here to get an estimate.
148        #[cfg(unix)]
149        {
150            let ptr_size = mem::size_of::<usize>();
151            // arg + \0 + pointer
152            let args_size = self.args.iter().fold(0usize, |acc, a| {
153                let arg = a.as_encoded_bytes().len();
154                let nul = 1;
155                acc.saturating_add(arg).saturating_add(nul).saturating_add(ptr_size)
156            });
157            // key + `=` + value + \0 + pointer
158            let envs_size = self.env.iter().fold(0usize, |acc, (k, v)| {
159                let k = k.as_encoded_bytes().len();
160                let eq = 1;
161                let v = v.as_encoded_bytes().len();
162                let nul = 1;
163                acc.saturating_add(k)
164                    .saturating_add(eq)
165                    .saturating_add(v)
166                    .saturating_add(nul)
167                    .saturating_add(ptr_size)
168            });
169            let arg_max = match unsafe { libc::sysconf(libc::_SC_ARG_MAX) } {
170                -1 => return false, // Go to OS anyway.
171                max => max as usize,
172            };
173            return args_size.saturating_add(envs_size) > arg_max;
174        }
175
176        // Ok so on Windows to spawn a process is 32,768 characters in its
177        // command line [1]. Unfortunately we don't actually have access to that
178        // as it's calculated just before spawning. Instead we perform a
179        // poor-man's guess as to how long our command line will be. We're
180        // assuming here that we don't have to escape every character...
181        //
182        // Turns out though that `cmd.exe` has even smaller limits, 8192
183        // characters [2]. Linkers can often be batch scripts (for example
184        // Emscripten, Gecko's current build system) which means that we're
185        // running through batch scripts. These linkers often just forward
186        // arguments elsewhere (and maybe tack on more), so if we blow 8192
187        // bytes we'll typically cause them to blow as well.
188        //
189        // Basically as a result just perform an inflated estimate of what our
190        // command line will look like and test if it's > 8192 (we actually
191        // test against 6k to artificially inflate our estimate). If all else
192        // fails we'll fall back to the normal unix logic of testing the OS
193        // error code if we fail to spawn and automatically re-spawning the
194        // linker with smaller arguments.
195        //
196        // [1]: https://docs.microsoft.com/en-us/windows/win32/api/processthreadsapi/nf-processthreadsapi-createprocessa
197        // [2]: https://devblogs.microsoft.com/oldnewthing/?p=41553
198        #[cfg(windows)]
199        {
200            let estimated_command_line_len = self
201                .args
202                .iter()
203                .fold(0usize, |acc, a| acc.saturating_add(a.as_encoded_bytes().len()));
204            return estimated_command_line_len > 1024 * 6;
205        }
206    }
207}
208
209impl fmt::Debug for Command {
210    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
211        self.command().fmt(f)
212    }
213}
rustc_codegen_ssa/back/command.rs

rustc_codegen_ssa/back/
command.rs
