libc/config/linux/app.h

   1 //===-- Classes to capture properites of linux applications -----*- C++ -*-===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #ifndef LLVM_LIBC_CONFIG_LINUX_APP_H
  10 #define LLVM_LIBC_CONFIG_LINUX_APP_H
  11
  12 #include "src/__support/macros/config.h"
  13 #include "src/__support/macros/properties/architectures.h"
  14
  15 #include <stdint.h>
  16
  17 namespace LIBC_NAMESPACE_DECL {
  18
  19 // Data structure to capture properties of the linux/ELF TLS image.
  20 struct TLSImage {
  21   // The load address of the TLS.
  22   uintptr_t address;
  23
  24   // The byte size of the TLS image consisting of both initialized and
  25   // uninitialized memory. In ELF executables, it is size of .tdata + size of
  26   // .tbss. Put in another way, it is the memsz field of the PT_TLS header.
  27   uintptr_t size;
  28
  29   // The byte size of initialized memory in the TLS image. In ELF exectubles,
  30   // this is the size of .tdata. Put in another way, it is the filesz of the
  31   // PT_TLS header.
  32   uintptr_t init_size;
  33
  34   // The alignment of the TLS layout. It assumed that the alignment
  35   // value is a power of 2.
  36   uintptr_t align;
  37 };
  38
  39 // Linux manpage on `proc(5)` says that the aux vector is an array of
  40 // unsigned long pairs.
  41 // (see: https://man7.org/linux/man-pages/man5/proc.5.html)
  42 using AuxEntryType = unsigned long;
  43 // Using the naming convention from `proc(5)`.
  44 // TODO: Would be nice to use the aux entry structure from elf.h when available.
  45 struct AuxEntry {
  46   AuxEntryType id;
  47   AuxEntryType value;
  48 };
  49
  50 struct Args {
  51   uintptr_t argc;
  52
  53   // A flexible length array would be more suitable here, but C++ doesn't have
  54   // flexible arrays: P1039 proposes to fix this. So, for now we just fake it.
  55   // Even if argc is zero, "argv[argc] shall be a null pointer"
  56   // (ISO C 5.1.2.2.1) so one is fine. Also, length of 1 is not really wrong as
  57   // |argc| is guaranteed to be atleast 1, and there is an 8-byte null entry at
  58   // the end of the argv array.
  59   uintptr_t argv[1];
  60 };
  61
  62 // Data structure which captures properties of a linux application.
  63 struct AppProperties {
  64   // Page size used for the application.
  65   uintptr_t page_size;
  66
  67   Args *args;
  68
  69   // The properties of an application's TLS image.
  70   TLSImage tls;
  71
  72   // Environment data.
  73   uintptr_t *env_ptr;
  74
  75   // Auxiliary vector data.
  76   AuxEntry *auxv_ptr;
  77 };
  78
  79 [[gnu::weak]] extern AppProperties app;
  80
  81 // The descriptor of a thread's TLS area.
  82 struct TLSDescriptor {
  83   // The size of the TLS area.
  84   uintptr_t size = 0;
  85
  86   // The address of the TLS area. This address can be passed to cleanup
  87   // functions like munmap.
  88   uintptr_t addr = 0;
  89
  90   // The value the thread pointer register should be initialized to.
  91   // Note that, dependending the target architecture ABI, it can be the
  92   // same as |addr| or something else.
  93   uintptr_t tp = 0;
  94
  95   constexpr TLSDescriptor() = default;
  96 };
  97
  98 // Create and initialize the TLS area for the current thread. Should not
  99 // be called before app.tls has been initialized.
 100 void init_tls(TLSDescriptor &tls);
 101
 102 // Cleanup the TLS area as described in |tls_descriptor|.
 103 void cleanup_tls(uintptr_t tls_addr, uintptr_t tls_size);
 104
 105 // Set the thread pointer for the current thread.
 106 bool set_thread_ptr(uintptr_t val);
 107
 108 } // namespace LIBC_NAMESPACE_DECL
 109
 110 #endif // LLVM_LIBC_CONFIG_LINUX_APP_H