rustc_codegen_llvm/back/
archive.rs

1//! A helper class for dealing with static archives
2
3use std::ffi::{CStr, c_char, c_void};
4use std::io;
5
6use rustc_codegen_ssa::back::archive::{
7    ArArchiveBuilder, ArchiveBuilder, ArchiveBuilderBuilder, DEFAULT_OBJECT_READER, ObjectReader,
8};
9use rustc_session::Session;
10
11use crate::llvm;
12
13pub(crate) struct LlvmArchiveBuilderBuilder;
14
15impl ArchiveBuilderBuilder for LlvmArchiveBuilderBuilder {
16    fn new_archive_builder<'a>(&self, sess: &'a Session) -> Box<dyn ArchiveBuilder + 'a> {
17        // Use the `object` crate to build archives, with a little bit of help from LLVM.
18        Box::new(ArArchiveBuilder::new(sess, &LLVM_OBJECT_READER))
19    }
20}
21
22// The object crate doesn't know how to get symbols for LLVM bitcode and COFF bigobj files.
23// As such we need to use LLVM for them.
24
25static LLVM_OBJECT_READER: ObjectReader = ObjectReader {
26    get_symbols: get_llvm_object_symbols,
27    is_64_bit_object_file: llvm_is_64_bit_object_file,
28    is_ec_object_file: llvm_is_ec_object_file,
29    is_any_arm64_coff: llvm_is_any_arm64_coff,
30    get_xcoff_member_alignment: DEFAULT_OBJECT_READER.get_xcoff_member_alignment,
31};
32
33#[deny(unsafe_op_in_unsafe_fn)]
34fn get_llvm_object_symbols(
35    buf: &[u8],
36    f: &mut dyn FnMut(&[u8]) -> io::Result<()>,
37) -> io::Result<bool> {
38    let mut state = Box::new(f);
39
40    let err = unsafe {
41        llvm::LLVMRustGetSymbols(
42            buf.as_ptr(),
43            buf.len(),
44            (&raw mut *state) as *mut c_void,
45            callback,
46            error_callback,
47        )
48    };
49
50    if err.is_null() {
51        return Ok(true);
52    } else {
53        let error = unsafe { *Box::from_raw(err as *mut io::Error) };
54        // These are the magic constants for LLVM bitcode files:
55        // https://github.com/llvm/llvm-project/blob/7eadc1960d199676f04add402bb0aa6f65b7b234/llvm/lib/BinaryFormat/Magic.cpp#L90-L97
56        if buf.starts_with(&[0xDE, 0xCE, 0x17, 0x0B]) || buf.starts_with(&[b'B', b'C', 0xC0, 0xDE])
57        {
58            // For LLVM bitcode, failure to read the symbols is not fatal. The bitcode may have been
59            // produced by a newer LLVM version that the one linked to rustc. This is fine provided
60            // that the linker does use said newer LLVM version. We skip writing the symbols for the
61            // bitcode to the symbol table of the archive. Traditional linkers don't like this, but
62            // newer linkers like lld, mold and wild ignore the symbol table anyway, so if they link
63            // against a new enough LLVM it will work out in the end.
64            // LLVM's archive writer also has this same behavior of only warning about invalid
65            // bitcode since https://github.com/llvm/llvm-project/pull/96848
66
67            // We don't have access to the DiagCtxt here to produce a nice warning in the correct format.
68            eprintln!("warning: Failed to read symbol table from LLVM bitcode: {}", error);
69            return Ok(true);
70        } else {
71            return Err(error);
72        }
73    }
74
75    unsafe extern "C" fn callback(state: *mut c_void, symbol_name: *const c_char) -> *mut c_void {
76        let f = unsafe { &mut *(state as *mut &mut dyn FnMut(&[u8]) -> io::Result<()>) };
77        match f(unsafe { CStr::from_ptr(symbol_name) }.to_bytes()) {
78            Ok(()) => std::ptr::null_mut(),
79            Err(err) => Box::into_raw(Box::new(err) as Box<io::Error>) as *mut c_void,
80        }
81    }
82
83    unsafe extern "C" fn error_callback(error: *const c_char) -> *mut c_void {
84        let error = unsafe { CStr::from_ptr(error) };
85        Box::into_raw(Box::new(io::Error::new(
86            io::ErrorKind::Other,
87            format!("LLVM error: {}", error.to_string_lossy()),
88        )) as Box<io::Error>) as *mut c_void
89    }
90}
91
92fn llvm_is_64_bit_object_file(buf: &[u8]) -> bool {
93    unsafe { llvm::LLVMRustIs64BitSymbolicFile(buf.as_ptr(), buf.len()) }
94}
95
96fn llvm_is_ec_object_file(buf: &[u8]) -> bool {
97    unsafe { llvm::LLVMRustIsECObject(buf.as_ptr(), buf.len()) }
98}
99
100fn llvm_is_any_arm64_coff(buf: &[u8]) -> bool {
101    unsafe { llvm::LLVMRustIsAnyArm64Coff(buf.as_ptr(), buf.len()) }
102}
rustc_codegen_llvm/back/archive.rs

rustc_codegen_llvm/back/
archive.rs
