/*
* OS specific utility functions
* (C) 2015,2016,2017,2018 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/

#ifndef BOTAN_OS_UTILS_H_
#define BOTAN_OS_UTILS_H_

#include <botan/types.h>
#include <functional>
#include <string>
#include <vector>

#if defined(BOTAN_TARGET_OS_HAS_THREADS)
   #include <thread>
#endif

namespace Botan::OS {

/*
* This header is internal (not installed) and these functions are not
* intended to be called by applications. However they are given public
* visibility (using BOTAN_TEST_API macro) for the tests. This also probably
* allows them to be overridden by the application on ELF systems, but
* this hasn't been tested.
*/

/**
* @return process ID assigned by the operating system.
*
* On Unix and Windows systems, this always returns a result
*
* On systems where there is no processes to speak of (for example on baremetal
* systems or within a unikernel), this function returns zero.
*/
uint32_t BOTAN_TEST_API get_process_id();

/**
* Test if we are currently running with elevated permissions
* eg setuid, setgid, or with POSIX caps set.
*/
bool running_in_privileged_state();

/**
* @return CPU processor clock, if available
*
* On Windows, calls QueryPerformanceCounter.
*
* Under GCC or Clang on supported platforms the hardware cycle counter is queried.
* Currently supported processors are x86, PPC, Alpha, SPARC, IA-64, S/390x, and HP-PA.
* If no CPU cycle counter is available on this system, returns zero.
*/
uint64_t BOTAN_TEST_API get_cpu_cycle_counter();

size_t BOTAN_TEST_API get_cpu_available();

/**
* Return the ELF auxiliary vector cooresponding to the given ID.
* This only makes sense on Unix-like systems and is currently
* only supported on Linux, Android, and FreeBSD.
*
* Returns zero if not supported on the current system or if
* the id provided is not known.
*/
unsigned long get_auxval(unsigned long id);

/*
* @return best resolution timestamp available
*
* The epoch and update rate of this clock is arbitrary and depending
* on the hardware it may not tick at a constant rate.
*
* Uses hardware cycle counter, if available.
* On POSIX platforms clock_gettime is used with a monotonic timer
* As a final fallback std::chrono::high_resolution_clock is used.
*/
uint64_t BOTAN_TEST_API get_high_resolution_clock();

/**
* @return system clock (reflecting wall clock) with best resolution
* available, normalized to nanoseconds resolution.
*/
uint64_t BOTAN_TEST_API get_system_timestamp_ns();

/**
* @return maximum amount of memory (in bytes) Botan could/should
* hyptothetically allocate for the memory poool. Reads environment
* variable "BOTAN_MLOCK_POOL_SIZE", set to "0" to disable pool.
*/
size_t get_memory_locking_limit();

/**
* Return the size of a memory page, if that can be derived on the
* current system. Otherwise returns some default value (eg 4096)
*/
size_t system_page_size();

/**
* Read the value of an environment variable, setting it to value_out if it
* exists.  Returns false and sets value_out to empty string if no such variable
* is set. If the process seems to be running in a privileged state (such as
* setuid) then always returns false and does not examine the environment.
*/
bool read_env_variable(std::string& value_out, std::string_view var_name);

/**
* Read the value of an environment variable and convert it to an
* integer. If not set or conversion fails, returns the default value.
*
* If the process seems to be running in a privileged state (such as setuid)
* then always returns nullptr, similiar to glibc's secure_getenv.
*/
size_t read_env_variable_sz(std::string_view var_name, size_t def_value = 0);

/**
* Request count pages of RAM which are locked into memory using mlock,
* VirtualLock, or some similar OS specific API. Free it with free_locked_pages.
*
* Returns an empty list on failure. This function is allowed to return fewer
* than count pages.
*
* The contents of the allocated pages are undefined.
*
* Each page is preceded by and followed by a page which is marked
* as noaccess, such that accessing it will cause a crash. This turns
* out of bound reads/writes into crash events.
*
* @param count requested number of locked pages
*/
std::vector<void*> allocate_locked_pages(size_t count);

/**
* Free memory allocated by allocate_locked_pages
* @param pages a list of pages returned by allocate_locked_pages
*/
void free_locked_pages(const std::vector<void*>& pages);

/**
* Set the MMU to prohibit access to this page
*/
void page_prohibit_access(void* page);

/**
* Set the MMU to allow R/W access to this page
*/
void page_allow_access(void* page);

/**
* Set a ID to a page's range expressed by size bytes
*/
void page_named(void* page, size_t size);

#if defined(BOTAN_TARGET_OS_HAS_THREADS)
void set_thread_name(std::thread& thread, const std::string& name);
#endif

/**
* Run a probe instruction to test for support for a CPU instruction.
* Runs in system-specific env that catches illegal instructions; this
* function always fails if the OS doesn't provide this.
* Returns value of probe_fn, if it could run.
* If error occurs, returns negative number.
* This allows probe_fn to indicate errors of its own, if it wants.
* For example the instruction might not only be only available on some
* CPUs, but also buggy on some subset of these - the probe function
* can test to make sure the instruction works properly before
* indicating that the instruction is available.
*
* @warning on Unix systems uses signal handling in a way that is not
* thread safe. It should only be called in a single-threaded context
* (ie, at static init time).
*
* If probe_fn throws an exception the result is undefined.
*
* Return codes:
* -1 illegal instruction detected
*/
int BOTAN_TEST_API run_cpu_instruction_probe(const std::function<int()>& probe_fn);

/**
* Represents a terminal state
*/
class BOTAN_UNSTABLE_API Echo_Suppression {
   public:
      /**
      * Reenable echo on this terminal. Can be safely called
      * multiple times. May throw if an error occurs.
      */
      virtual void reenable_echo() = 0;

      /**
      * Implicitly calls reenable_echo, but swallows/ignored all
      * errors which would leave the terminal in an invalid state.
      */
      virtual ~Echo_Suppression() = default;
};

/**
* Suppress echo on the terminal
* Returns null if this operation is not supported on the current system.
*/
std::unique_ptr<Echo_Suppression> BOTAN_UNSTABLE_API suppress_echo_on_terminal();

}  // namespace Botan::OS

#endif
