cregit-Linux how code gets into the kernel

Release 4.10 tools/testing/selftests/size/get_size.c

/*
 * Copyright 2014 Sony Mobile Communications Inc.
 *
 * Licensed under the terms of the GNU GPL License version 2
 *
 * Selftest for runtime system size
 *
 * Prints the amount of RAM that the currently running system is using.
 *
 * This program tries to be as small as possible itself, to
 * avoid perturbing the system memory utilization with its
 * own execution.  It also attempts to have as few dependencies
 * on kernel features as possible.
 *
 * It should be statically linked, with startup libs avoided.
 * It uses no library calls, and only the following 3 syscalls:
 *   sysinfo(), write(), and _exit()
 *
 * For output, it avoids printf (which in some C libraries
 * has large external dependencies) by  implementing it's own
 * number output and print routines, and using __builtin_strlen()
 */

#include <sys/sysinfo.h>
#include <unistd.h>


#define STDOUT_FILENO 1


static int print(const char *s) { return write(STDOUT_FILENO, s, __builtin_strlen(s)); }

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static inline char *num_to_str(unsigned long num, char *buf, int len) { unsigned int digit; /* put digits in buffer from back to front */ buf += len - 1; *buf = 0; do { digit = num % 10; *(--buf) = digit + '0'; num /= 10; } while (num > 0); return buf; }

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static int print_num(unsigned long num) { char num_buf[30]; return print(num_to_str(num, num_buf, sizeof(num_buf))); }

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static int print_k_value(const char *s, unsigned long num, unsigned long units) { unsigned long long temp; int ccode; print(s); temp = num; temp = (temp * units)/1024; num = temp; ccode = print_num(num); print("\n"); return ccode; }

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/* this program has no main(), as startup libraries are not used */
void _start(void) { int ccode; struct sysinfo info; unsigned long used; print("Testing system size.\n"); print("1..1\n"); ccode = sysinfo(&info); if (ccode < 0) { print("not ok 1 get runtime memory use\n"); print("# could not get sysinfo\n"); _exit(ccode); } /* ignore cache complexities for now */ used = info.totalram - info.freeram - info.bufferram; print_k_value("ok 1 get runtime memory use # size = ", used, info.mem_unit); print("# System runtime memory report (units in Kilobytes):\n"); print_k_value("# Total: ", info.totalram, info.mem_unit); print_k_value("# Free: ", info.freeram, info.mem_unit); print_k_value("# Buffer: ", info.bufferram, info.mem_unit); print_k_value("# In use: ", used, info.mem_unit); _exit(0); }

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