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//! TLS utilities.
//!
//! # Safety
//!
//! This file contains code that reads the raw phdr array pointed to by the
//! kernel-provided AUXV values.
#![allow(unsafe_code)]
use crate::backend::c;
use crate::backend::param::auxv::exe_phdrs;
use core::arch::global_asm;
use core::ptr::{null, NonNull};
use linux_raw_sys::elf::*;
/// For use with [`set_thread_area`].
///
/// [`set_thread_area`]: crate::runtime::set_thread_area
#[cfg(target_arch = "x86")]
pub type UserDesc = linux_raw_sys::general::user_desc;
pub(crate) fn startup_tls_info() -> StartupTlsInfo {
let mut base = null();
let mut tls_phdr = null();
let mut stack_size = 0;
let (first_phdr, phent, phnum) = exe_phdrs();
let mut current_phdr = first_phdr.cast::<Elf_Phdr>();
// The dynamic address of the dynamic section, which we can compare with
// the `PT_DYNAMIC` header's static address, if present.
let dynamic_addr: *const c::c_void = unsafe { &_DYNAMIC };
// SAFETY: We assume the phdr array pointer and length the kernel provided
// to the process describe a valid phdr array.
unsafe {
let phdrs_end = current_phdr.cast::<u8>().add(phnum * phent).cast();
while current_phdr != phdrs_end {
let phdr = &*current_phdr;
current_phdr = current_phdr.cast::<u8>().add(phent).cast();
match phdr.p_type {
// Compute the offset from the static virtual addresses
// in the `p_vaddr` fields to the dynamic addresses. We don't
// always get a `PT_PHDR` or `PT_DYNAMIC` header, so use
// whichever one we get.
PT_PHDR => base = first_phdr.cast::<u8>().wrapping_sub(phdr.p_vaddr),
PT_DYNAMIC => base = dynamic_addr.cast::<u8>().wrapping_sub(phdr.p_vaddr),
PT_TLS => tls_phdr = phdr,
PT_GNU_STACK => stack_size = phdr.p_memsz,
_ => {}
}
}
if tls_phdr.is_null() {
StartupTlsInfo {
addr: NonNull::dangling().as_ptr(),
mem_size: 0,
file_size: 0,
align: 1,
stack_size: 0,
}
} else {
StartupTlsInfo {
addr: base.cast::<u8>().wrapping_add((*tls_phdr).p_vaddr).cast(),
mem_size: (*tls_phdr).p_memsz,
file_size: (*tls_phdr).p_filesz,
align: (*tls_phdr).p_align,
stack_size,
}
}
}
}
extern "C" {
/// Declare the `_DYNAMIC` symbol so that we can compare its address with
/// the static address in the `PT_DYNAMIC` header to learn our offset. Use
/// a weak symbol because `_DYNAMIC` is not always present.
static _DYNAMIC: c::c_void;
}
// Rust has `extern_weak` but it isn't stable, so use a `global_asm`.
global_asm!(".weak _DYNAMIC");
/// The values returned from [`startup_tls_info`].
///
/// [`startup_tls_info`]: crate::runtime::startup_tls_info
pub struct StartupTlsInfo {
/// The base address of the TLS segment.
pub addr: *const c::c_void,
/// The size of the memory region.
pub mem_size: usize,
/// The size beyond which all memory is zero-initialized.
pub file_size: usize,
/// The required alignment for the TLS segment.
pub align: usize,
/// The requested minimum size for stacks.
pub stack_size: usize,
}
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