library/std/src/sys/common/alloc.rs

   1 use crate::alloc::{GlobalAlloc, Layout, System};
   2 use crate::cmp;
   3 use crate::ptr;
   4
   5 // The minimum alignment guaranteed by the architecture. This value is used to
   6 // add fast paths for low alignment values.
   7 #[cfg(all(any(
   8     target_arch = "x86",
   9     target_arch = "arm",
  10     target_arch = "mips",
  11     target_arch = "powerpc",
  12     target_arch = "powerpc64",
  13     target_arch = "sparc",
  14     target_arch = "asmjs",
  15     target_arch = "wasm32",
  16     target_arch = "hexagon",
  17     all(target_arch = "riscv32", not(target_os = "espidf")),
  18     all(target_arch = "xtensa", not(target_os = "espidf")),
  19 )))]
  20 pub const MIN_ALIGN: usize = 8;
  21 #[cfg(all(any(
  22     target_arch = "x86_64",
  23     target_arch = "aarch64",
  24     target_arch = "mips64",
  25     target_arch = "s390x",
  26     target_arch = "sparc64",
  27     target_arch = "riscv64",
  28     target_arch = "wasm64",
  29 )))]
  30 pub const MIN_ALIGN: usize = 16;
  31 // The allocator on the esp-idf platform guarantees 4 byte alignment.
  32 #[cfg(all(any(
  33     all(target_arch = "riscv32", target_os = "espidf"),
  34     all(target_arch = "xtensa", target_os = "espidf"),
  35 )))]
  36 pub const MIN_ALIGN: usize = 4;
  37
  38 pub unsafe fn realloc_fallback(
  39     alloc: &System,
  40     ptr: *mut u8,
  41     old_layout: Layout,
  42     new_size: usize,
  43 ) -> *mut u8 {
  44     // Docs for GlobalAlloc::realloc require this to be valid:
  45     let new_layout = Layout::from_size_align_unchecked(new_size, old_layout.align());
  46
  47     let new_ptr = GlobalAlloc::alloc(alloc, new_layout);
  48     if !new_ptr.is_null() {
  49         let size = cmp::min(old_layout.size(), new_size);
  50         ptr::copy_nonoverlapping(ptr, new_ptr, size);
  51         GlobalAlloc::dealloc(alloc, ptr, old_layout);
  52     }
  53     new_ptr
  54 }