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Rollup merge of #138783 - bjorn3:cache_current_dll_path, r=lqd

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Cache current_dll_path output

Computing the current dll path is somewhat expensive relative to other work when compiling `fn main() {}` as `dladdr` needs to iterate over the symbol table of librustc_driver.so until it finds a match.
This commit is contained in:
Jacob Pratt 2025-03-23 20:44:12 -04:00 • committed by GitHub
commit ab138e6aa8
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1 changed files with 64 additions and 54 deletions
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118
compiler/rustc_session/src/filesearch.rs
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@ -60,66 +60,76 @@ pub fn make_target_bin_path(sysroot: &Path, target_triple: &str) -> PathBuf {
#[cfg(unix)]
fn current_dll_path() -> Result<PathBuf, String> {
use std::ffi::{CStr, OsStr};
use std::os::unix::prelude::*;
use std::sync::OnceLock;
#[cfg(not(target_os = "aix"))]
unsafe {
let addr = current_dll_path as usize as *mut _;
let mut info = std::mem::zeroed();
if libc::dladdr(addr, &mut info) == 0 {
return Err("dladdr failed".into());
}
if info.dli_fname.is_null() {
return Err("dladdr returned null pointer".into());
}
let bytes = CStr::from_ptr(info.dli_fname).to_bytes();
let os = OsStr::from_bytes(bytes);
Ok(PathBuf::from(os))
}
// This is somewhat expensive relative to other work when compiling `fn main() {}` as `dladdr`
// needs to iterate over the symbol table of librustc_driver.so until it finds a match.
// As such cache this to avoid recomputing if we try to get the sysroot in multiple places.
static CURRENT_DLL_PATH: OnceLock<Result<PathBuf, String>> = OnceLock::new();
CURRENT_DLL_PATH
.get_or_init(|| {
use std::ffi::{CStr, OsStr};
use std::os::unix::prelude::*;
#[cfg(target_os = "aix")]
unsafe {
// On AIX, the symbol `current_dll_path` references a function descriptor.
// A function descriptor is consisted of (See https://reviews.llvm.org/D62532)
// * The address of the entry point of the function.
// * The TOC base address for the function.
// * The environment pointer.
// The function descriptor is in the data section.
let addr = current_dll_path as u64;
let mut buffer = vec![std::mem::zeroed::<libc::ld_info>(); 64];
loop {
if libc::loadquery(
libc::L_GETINFO,
buffer.as_mut_ptr() as *mut u8,
(size_of::<libc::ld_info>() * buffer.len()) as u32,
) >= 0
{
break;
} else {
if std::io::Error::last_os_error().raw_os_error().unwrap() != libc::ENOMEM {
return Err("loadquery failed".into());
#[cfg(not(target_os = "aix"))]
unsafe {
let addr = current_dll_path as usize as *mut _;
let mut info = std::mem::zeroed();
if libc::dladdr(addr, &mut info) == 0 {
return Err("dladdr failed".into());
}
buffer.resize(buffer.len() * 2, std::mem::zeroed::<libc::ld_info>());
}
}
let mut current = buffer.as_mut_ptr() as *mut libc::ld_info;
loop {
let data_base = (*current).ldinfo_dataorg as u64;
let data_end = data_base + (*current).ldinfo_datasize;
if (data_base..data_end).contains(&addr) {
let bytes = CStr::from_ptr(&(*current).ldinfo_filename[0]).to_bytes();
if info.dli_fname.is_null() {
return Err("dladdr returned null pointer".into());
}
let bytes = CStr::from_ptr(info.dli_fname).to_bytes();
let os = OsStr::from_bytes(bytes);
return Ok(PathBuf::from(os));
Ok(PathBuf::from(os))
}
if (*current).ldinfo_next == 0 {
break;
#[cfg(target_os = "aix")]
unsafe {
// On AIX, the symbol `current_dll_path` references a function descriptor.
// A function descriptor is consisted of (See https://reviews.llvm.org/D62532)
// * The address of the entry point of the function.
// * The TOC base address for the function.
// * The environment pointer.
// The function descriptor is in the data section.
let addr = current_dll_path as u64;
let mut buffer = vec![std::mem::zeroed::<libc::ld_info>(); 64];
loop {
if libc::loadquery(
libc::L_GETINFO,
buffer.as_mut_ptr() as *mut u8,
(size_of::<libc::ld_info>() * buffer.len()) as u32,
) >= 0
{
break;
} else {
if std::io::Error::last_os_error().raw_os_error().unwrap() != libc::ENOMEM {
return Err("loadquery failed".into());
}
buffer.resize(buffer.len() * 2, std::mem::zeroed::<libc::ld_info>());
}
}
let mut current = buffer.as_mut_ptr() as *mut libc::ld_info;
loop {
let data_base = (*current).ldinfo_dataorg as u64;
let data_end = data_base + (*current).ldinfo_datasize;
if (data_base..data_end).contains(&addr) {
let bytes = CStr::from_ptr(&(*current).ldinfo_filename[0]).to_bytes();
let os = OsStr::from_bytes(bytes);
return Ok(PathBuf::from(os));
}
if (*current).ldinfo_next == 0 {
break;
}
current = (current as *mut i8).offset((*current).ldinfo_next as isize)
as *mut libc::ld_info;
}
return Err(format!("current dll's address {} is not in the load map", addr));
}
current =
(current as *mut i8).offset((*current).ldinfo_next as isize) as *mut libc::ld_info;
}
return Err(format!("current dll's address {} is not in the load map", addr));
}
})
.clone()
}
#[cfg(windows)]