What happens when I build code in C?
Contents
17. What happens when I build code in C?¶
We came across the term build before.
We sometimes say that compiling takes code from source to executable, but this process is actually multiple stages and compiling is one of those steps.
We will focus on what has to happen more than how it all happens.
CSC301, 402, 501, 502 go into greater detail on how languages work.
Our goal is to:
(where applicable) give you a preview
get enough understanding of what happens to know where to look when debugging
17.1. Setup¶
Let’s setup by creating an empty folder
cd Documents/sysinclass/
mkdir compilec
cd compilec/
and then create a small program in C.
nano hello.c
and then we can look at the file
cat hello.c
#include <stdio.h>
void main () {
printf("Hello world\n");
}
17.2. Preprocessing¶
First we handle the preprocessing which pulls in headers that are included. We will use the compiler gcc
gcc -E hello.c -o hello.i
If it succeeds, we see no output, but we can check the folder
ls
now we have a new file
hello.c hello.i
cat hello.i
This gives us a version with the header file’s contents literally pasted in to replace the original #include statement
# 1 "hello.c"
# 1 "<built-in>" 1
# 1 "<built-in>" 3
# 366 "<built-in>" 3
# 1 "<command line>" 1
# 1 "<built-in>" 2
# 1 "hello.c" 2
# 1 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/stdio.h" 1 3 4
# 64 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/stdio.h" 3 4
# 1 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/_stdio.h" 1 3 4
# 68 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/_stdio.h" 3 4
# 1 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/cdefs.h" 1 3 4
# 630 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/cdefs.h" 3 4
# 1 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_symbol_aliasing.h" 1 3 4
# 631 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/cdefs.h" 2 3 4
# 696 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/cdefs.h" 3 4
# 1 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_posix_availability.h" 1 3 4
# 697 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/cdefs.h" 2 3 4
# 69 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/_stdio.h" 2 3 4
# 1 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/Availability.h" 1 3 4
# 259 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/Availability.h" 3 4
# 1 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/AvailabilityInternal.h" 1 3 4
# 260 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/Availability.h" 2 3 4
# 70 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/_stdio.h" 2 3 4
# 1 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/_types.h" 1 3 4
# 27 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/_types.h" 3 4
# 1 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_types.h" 1 3 4
# 33 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_types.h" 3 4
# 1 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/machine/_types.h" 1 3 4
# 32 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/machine/_types.h" 3 4
# 1 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/i386/_types.h" 1 3 4
# 37 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/i386/_types.h" 3 4
typedef signed char __int8_t;
typedef unsigned char __uint8_t;
typedef short __int16_t;
typedef unsigned short __uint16_t;
typedef int __int32_t;
typedef unsigned int __uint32_t;
typedef long long __int64_t;
typedef unsigned long long __uint64_t;
typedef long __darwin_intptr_t;
typedef unsigned int __darwin_natural_t;
# 70 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/i386/_types.h" 3 4
typedef int __darwin_ct_rune_t;
typedef union {
char __mbstate8[128];
long long _mbstateL;
} __mbstate_t;
typedef __mbstate_t __darwin_mbstate_t;
typedef long int __darwin_ptrdiff_t;
typedef long unsigned int __darwin_size_t;
typedef __builtin_va_list __darwin_va_list;
typedef int __darwin_wchar_t;
typedef __darwin_wchar_t __darwin_rune_t;
typedef int __darwin_wint_t;
typedef unsigned long __darwin_clock_t;
typedef __uint32_t __darwin_socklen_t;
typedef long __darwin_ssize_t;
typedef long __darwin_time_t;
# 33 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/machine/_types.h" 2 3 4
# 34 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_types.h" 2 3 4
# 55 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_types.h" 3 4
typedef __int64_t __darwin_blkcnt_t;
typedef __int32_t __darwin_blksize_t;
typedef __int32_t __darwin_dev_t;
typedef unsigned int __darwin_fsblkcnt_t;
typedef unsigned int __darwin_fsfilcnt_t;
typedef __uint32_t __darwin_gid_t;
typedef __uint32_t __darwin_id_t;
typedef __uint64_t __darwin_ino64_t;
typedef __darwin_ino64_t __darwin_ino_t;
typedef __darwin_natural_t __darwin_mach_port_name_t;
typedef __darwin_mach_port_name_t __darwin_mach_port_t;
typedef __uint16_t __darwin_mode_t;
typedef __int64_t __darwin_off_t;
typedef __int32_t __darwin_pid_t;
typedef __uint32_t __darwin_sigset_t;
typedef __int32_t __darwin_suseconds_t;
typedef __uint32_t __darwin_uid_t;
typedef __uint32_t __darwin_useconds_t;
typedef unsigned char __darwin_uuid_t[16];
typedef char __darwin_uuid_string_t[37];
# 1 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_pthread/_pthread_types.h" 1 3 4
# 57 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_pthread/_pthread_types.h" 3 4
struct __darwin_pthread_handler_rec {
void (*__routine)(void *);
void *__arg;
struct __darwin_pthread_handler_rec *__next;
};
struct _opaque_pthread_attr_t {
long __sig;
char __opaque[56];
};
struct _opaque_pthread_cond_t {
long __sig;
char __opaque[40];
};
struct _opaque_pthread_condattr_t {
long __sig;
char __opaque[8];
};
struct _opaque_pthread_mutex_t {
long __sig;
char __opaque[56];
};
struct _opaque_pthread_mutexattr_t {
long __sig;
char __opaque[8];
};
struct _opaque_pthread_once_t {
long __sig;
char __opaque[8];
};
struct _opaque_pthread_rwlock_t {
long __sig;
char __opaque[192];
};
struct _opaque_pthread_rwlockattr_t {
long __sig;
char __opaque[16];
};
struct _opaque_pthread_t {
long __sig;
struct __darwin_pthread_handler_rec *__cleanup_stack;
char __opaque[8176];
};
typedef struct _opaque_pthread_attr_t __darwin_pthread_attr_t;
typedef struct _opaque_pthread_cond_t __darwin_pthread_cond_t;
typedef struct _opaque_pthread_condattr_t __darwin_pthread_condattr_t;
typedef unsigned long __darwin_pthread_key_t;
typedef struct _opaque_pthread_mutex_t __darwin_pthread_mutex_t;
typedef struct _opaque_pthread_mutexattr_t __darwin_pthread_mutexattr_t;
typedef struct _opaque_pthread_once_t __darwin_pthread_once_t;
typedef struct _opaque_pthread_rwlock_t __darwin_pthread_rwlock_t;
typedef struct _opaque_pthread_rwlockattr_t __darwin_pthread_rwlockattr_t;
typedef struct _opaque_pthread_t *__darwin_pthread_t;
# 81 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_types.h" 2 3 4
# 28 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/_types.h" 2 3 4
# 40 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/_types.h" 3 4
typedef int __darwin_nl_item;
typedef int __darwin_wctrans_t;
typedef __uint32_t __darwin_wctype_t;
# 72 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/_stdio.h" 2 3 4
# 1 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_types/_va_list.h" 1 3 4
# 31 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_types/_va_list.h" 3 4
# 1 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/machine/types.h" 1 3 4
# 35 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/machine/types.h" 3 4
# 1 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/i386/types.h" 1 3 4
# 76 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/i386/types.h" 3 4
# 1 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_types/_int8_t.h" 1 3 4
# 30 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_types/_int8_t.h" 3 4
typedef signed char int8_t;
# 77 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/i386/types.h" 2 3 4
# 1 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_types/_int16_t.h" 1 3 4
# 30 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_types/_int16_t.h" 3 4
typedef short int16_t;
# 78 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/i386/types.h" 2 3 4
# 1 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_types/_int32_t.h" 1 3 4
# 30 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_types/_int32_t.h" 3 4
typedef int int32_t;
# 79 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/i386/types.h" 2 3 4
# 1 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_types/_int64_t.h" 1 3 4
# 30 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_types/_int64_t.h" 3 4
typedef long long int64_t;
# 80 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/i386/types.h" 2 3 4
# 1 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_types/_u_int8_t.h" 1 3 4
# 30 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_types/_u_int8_t.h" 3 4
typedef unsigned char u_int8_t;
# 82 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/i386/types.h" 2 3 4
# 1 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_types/_u_int16_t.h" 1 3 4
# 30 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_types/_u_int16_t.h" 3 4
typedef unsigned short u_int16_t;
# 83 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/i386/types.h" 2 3 4
# 1 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_types/_u_int32_t.h" 1 3 4
# 30 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_types/_u_int32_t.h" 3 4
typedef unsigned int u_int32_t;
# 84 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/i386/types.h" 2 3 4
# 1 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_types/_u_int64_t.h" 1 3 4
# 30 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_types/_u_int64_t.h" 3 4
typedef unsigned long long u_int64_t;
# 85 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/i386/types.h" 2 3 4
typedef int64_t register_t;
# 1 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_types/_intptr_t.h" 1 3 4
# 30 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_types/_intptr_t.h" 3 4
# 1 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/machine/types.h" 1 3 4
# 31 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_types/_intptr_t.h" 2 3 4
typedef __darwin_intptr_t intptr_t;
# 93 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/i386/types.h" 2 3 4
# 1 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_types/_uintptr_t.h" 1 3 4
# 30 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_types/_uintptr_t.h" 3 4
typedef unsigned long uintptr_t;
# 94 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/i386/types.h" 2 3 4
typedef u_int64_t user_addr_t;
typedef u_int64_t user_size_t;
typedef int64_t user_ssize_t;
typedef int64_t user_long_t;
typedef u_int64_t user_ulong_t;
typedef int64_t user_time_t;
typedef int64_t user_off_t;
typedef u_int64_t syscall_arg_t;
# 36 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/machine/types.h" 2 3 4
# 32 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_types/_va_list.h" 2 3 4
typedef __darwin_va_list va_list;
# 76 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/_stdio.h" 2 3 4
# 1 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_types/_size_t.h" 1 3 4
# 31 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_types/_size_t.h" 3 4
typedef __darwin_size_t size_t;
# 77 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/_stdio.h" 2 3 4
# 1 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_types/_null.h" 1 3 4
# 78 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/_stdio.h" 2 3 4
# 1 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/stdio.h" 1 3 4
# 39 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/stdio.h" 3 4
int renameat(int, const char *, int, const char *) __attribute__((availability(macosx,introduced=10.10)));
int renamex_np(const char *, const char *, unsigned int) __attribute__((availability(macosx,introduced=10.12))) __attribute__((availability(ios,introduced=10.0))) __attribute__((availability(tvos,introduced=10.0))) __attribute__((availability(watchos,introduced=3.0)));
int renameatx_np(int, const char *, int, const char *, unsigned int) __attribute__((availability(macosx,introduced=10.12))) __attribute__((availability(ios,introduced=10.0))) __attribute__((availability(tvos,introduced=10.0))) __attribute__((availability(watchos,introduced=3.0)));
# 80 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/_stdio.h" 2 3 4
typedef __darwin_off_t fpos_t;
# 92 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/_stdio.h" 3 4
struct __sbuf {
unsigned char *_base;
int _size;
};
struct __sFILEX;
# 126 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/_stdio.h" 3 4
typedef struct __sFILE {
unsigned char *_p;
int _r;
int _w;
short _flags;
short _file;
struct __sbuf _bf;
int _lbfsize;
void *_cookie;
int (* _Nullable _close)(void *);
int (* _Nullable _read) (void *, char *, int);
fpos_t (* _Nullable _seek) (void *, fpos_t, int);
int (* _Nullable _write)(void *, const char *, int);
struct __sbuf _ub;
struct __sFILEX *_extra;
int _ur;
unsigned char _ubuf[3];
unsigned char _nbuf[1];
struct __sbuf _lb;
int _blksize;
fpos_t _offset;
} FILE;
# 65 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/stdio.h" 2 3 4
extern FILE *__stdinp;
extern FILE *__stdoutp;
extern FILE *__stderrp;
# 142 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/stdio.h" 3 4
void clearerr(FILE *);
int fclose(FILE *);
int feof(FILE *);
int ferror(FILE *);
int fflush(FILE *);
int fgetc(FILE *);
int fgetpos(FILE * restrict, fpos_t *);
char *fgets(char * restrict, int, FILE *);
FILE *fopen(const char * restrict __filename, const char * restrict __mode) __asm("_" "fopen" );
int fprintf(FILE * restrict, const char * restrict, ...) __attribute__((__format__ (__printf__, 2, 3)));
int fputc(int, FILE *);
int fputs(const char * restrict, FILE * restrict) __asm("_" "fputs" );
size_t fread(void * restrict __ptr, size_t __size, size_t __nitems, FILE * restrict __stream);
FILE *freopen(const char * restrict, const char * restrict,
FILE * restrict) __asm("_" "freopen" );
int fscanf(FILE * restrict, const char * restrict, ...) __attribute__((__format__ (__scanf__, 2, 3)));
int fseek(FILE *, long, int);
int fsetpos(FILE *, const fpos_t *);
long ftell(FILE *);
size_t fwrite(const void * restrict __ptr, size_t __size, size_t __nitems, FILE * restrict __stream) __asm("_" "fwrite" );
int getc(FILE *);
int getchar(void);
char *gets(char *);
void perror(const char *) __attribute__((__cold__));
int printf(const char * restrict, ...) __attribute__((__format__ (__printf__, 1, 2)));
int putc(int, FILE *);
int putchar(int);
int puts(const char *);
int remove(const char *);
int rename (const char *__old, const char *__new);
void rewind(FILE *);
int scanf(const char * restrict, ...) __attribute__((__format__ (__scanf__, 1, 2)));
void setbuf(FILE * restrict, char * restrict);
int setvbuf(FILE * restrict, char * restrict, int, size_t);
int sprintf(char * restrict, const char * restrict, ...) __attribute__((__format__ (__printf__, 2, 3))) __attribute__((__availability__(swift, unavailable, message="Use snprintf instead.")));
int sscanf(const char * restrict, const char * restrict, ...) __attribute__((__format__ (__scanf__, 2, 3)));
FILE *tmpfile(void);
__attribute__((__availability__(swift, unavailable, message="Use mkstemp(3) instead.")))
__attribute__((__deprecated__("This function is provided for compatibility reasons only. Due to security concerns inherent in the design of tmpnam(3), it is highly recommended that you use mkstemp(3) instead.")))
char *tmpnam(char *);
int ungetc(int, FILE *);
int vfprintf(FILE * restrict, const char * restrict, va_list) __attribute__((__format__ (__printf__, 2, 0)));
int vprintf(const char * restrict, va_list) __attribute__((__format__ (__printf__, 1, 0)));
int vsprintf(char * restrict, const char * restrict, va_list) __attribute__((__format__ (__printf__, 2, 0))) __attribute__((__availability__(swift, unavailable, message="Use vsnprintf instead.")));
# 205 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/stdio.h" 3 4
# 1 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/_ctermid.h" 1 3 4
# 26 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/_ctermid.h" 3 4
char *ctermid(char *);
# 206 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/stdio.h" 2 3 4
FILE *fdopen(int, const char *) __asm("_" "fdopen" );
int fileno(FILE *);
# 228 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/stdio.h" 3 4
int pclose(FILE *) __attribute__((__availability__(swift, unavailable, message="Use posix_spawn APIs or NSTask instead.")));
FILE *popen(const char *, const char *) __asm("_" "popen" ) __attribute__((__availability__(swift, unavailable, message="Use posix_spawn APIs or NSTask instead.")));
# 249 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/stdio.h" 3 4
int __srget(FILE *);
int __svfscanf(FILE *, const char *, va_list) __attribute__((__format__ (__scanf__, 2, 0)));
int __swbuf(int, FILE *);
# 260 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/stdio.h" 3 4
inline __attribute__ ((__always_inline__)) int __sputc(int _c, FILE *_p) {
if (--_p->_w >= 0 || (_p->_w >= _p->_lbfsize && (char)_c != '\n'))
return (*_p->_p++ = _c);
else
return (__swbuf(_c, _p));
}
# 286 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/stdio.h" 3 4
void flockfile(FILE *);
int ftrylockfile(FILE *);
void funlockfile(FILE *);
int getc_unlocked(FILE *);
int getchar_unlocked(void);
int putc_unlocked(int, FILE *);
int putchar_unlocked(int);
int getw(FILE *);
int putw(int, FILE *);
__attribute__((__availability__(swift, unavailable, message="Use mkstemp(3) instead.")))
__attribute__((__deprecated__("This function is provided for compatibility reasons only. Due to security concerns inherent in the design of tempnam(3), it is highly recommended that you use mkstemp(3) instead.")))
char *tempnam(const char *__dir, const char *__prefix) __asm("_" "tempnam" );
# 324 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/stdio.h" 3 4
# 1 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_types/_off_t.h" 1 3 4
# 31 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_types/_off_t.h" 3 4
typedef __darwin_off_t off_t;
# 325 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/stdio.h" 2 3 4
int fseeko(FILE * __stream, off_t __offset, int __whence);
off_t ftello(FILE * __stream);
int snprintf(char * restrict __str, size_t __size, const char * restrict __format, ...) __attribute__((__format__ (__printf__, 3, 4)));
int vfscanf(FILE * restrict __stream, const char * restrict __format, va_list) __attribute__((__format__ (__scanf__, 2, 0)));
int vscanf(const char * restrict __format, va_list) __attribute__((__format__ (__scanf__, 1, 0)));
int vsnprintf(char * restrict __str, size_t __size, const char * restrict __format, va_list) __attribute__((__format__ (__printf__, 3, 0)));
int vsscanf(const char * restrict __str, const char * restrict __format, va_list) __attribute__((__format__ (__scanf__, 2, 0)));
# 349 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/stdio.h" 3 4
# 1 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_types/_ssize_t.h" 1 3 4
# 31 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_types/_ssize_t.h" 3 4
typedef __darwin_ssize_t ssize_t;
# 350 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/stdio.h" 2 3 4
int dprintf(int, const char * restrict, ...) __attribute__((__format__ (__printf__, 2, 3))) __attribute__((availability(macosx,introduced=10.7)));
int vdprintf(int, const char * restrict, va_list) __attribute__((__format__ (__printf__, 2, 0))) __attribute__((availability(macosx,introduced=10.7)));
ssize_t getdelim(char ** restrict __linep, size_t * restrict __linecapp, int __delimiter, FILE * restrict __stream) __attribute__((availability(macosx,introduced=10.7)));
ssize_t getline(char ** restrict __linep, size_t * restrict __linecapp, FILE * restrict __stream) __attribute__((availability(macosx,introduced=10.7)));
FILE *fmemopen(void * restrict __buf, size_t __size, const char * restrict __mode) __attribute__((availability(macos,introduced=10.13))) __attribute__((availability(ios,introduced=11.0))) __attribute__((availability(tvos,introduced=11.0))) __attribute__((availability(watchos,introduced=4.0)));
FILE *open_memstream(char **__bufp, size_t *__sizep) __attribute__((availability(macos,introduced=10.13))) __attribute__((availability(ios,introduced=11.0))) __attribute__((availability(tvos,introduced=11.0))) __attribute__((availability(watchos,introduced=4.0)));
# 367 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/stdio.h" 3 4
extern const int sys_nerr;
extern const char *const sys_errlist[];
int asprintf(char ** restrict, const char * restrict, ...) __attribute__((__format__ (__printf__, 2, 3)));
char *ctermid_r(char *);
char *fgetln(FILE *, size_t *);
const char *fmtcheck(const char *, const char *);
int fpurge(FILE *);
void setbuffer(FILE *, char *, int);
int setlinebuf(FILE *);
int vasprintf(char ** restrict, const char * restrict, va_list) __attribute__((__format__ (__printf__, 2, 0)));
FILE *zopen(const char *, const char *, int);
FILE *funopen(const void *,
int (* _Nullable)(void *, char *, int),
int (* _Nullable)(void *, const char *, int),
fpos_t (* _Nullable)(void *, fpos_t, int),
int (* _Nullable)(void *));
# 407 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/stdio.h" 3 4
# 1 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/secure/_stdio.h" 1 3 4
# 31 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/secure/_stdio.h" 3 4
# 1 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/secure/_common.h" 1 3 4
# 32 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/secure/_stdio.h" 2 3 4
# 42 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/secure/_stdio.h" 3 4
extern int __sprintf_chk (char * restrict, int, size_t,
const char * restrict, ...);
# 52 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/secure/_stdio.h" 3 4
extern int __snprintf_chk (char * restrict, size_t, int, size_t,
const char * restrict, ...);
extern int __vsprintf_chk (char * restrict, int, size_t,
const char * restrict, va_list);
extern int __vsnprintf_chk (char * restrict, size_t, int, size_t,
const char * restrict, va_list);
# 408 "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/stdio.h" 2 3 4
# 2 "hello.c" 2
void main () {
printf("Hello world\n");
}
At the bottom of the file, we see the orignal code with an extra bit of informaiton that helps the compiler write better error messages, by saying where contents came from.
17.3. Compiling¶
Next we take our preprocessed file and compile it to get assembly code.
gcc -S -c hello.i
hello.c:3:1: warning: return type of 'main' is not 'int' [-Wmain-return-type]
void main () {
^
hello.c:3:1: note: change return type to 'int'
void main () {
^~~~
int
1 warning generated.
ls
hello.c hello.i hello.s
cat hello.s
.section __TEXT,__text,regular,pure_instructions
.build_version macos, 10, 15, 6 sdk_version 10, 15, 6
.globl _main ## -- Begin function main
.p2align 4, 0x90
_main: ## @main
.cfi_startproc
## %bb.0:
pushq %rbp
.cfi_def_cfa_offset 16
.cfi_offset %rbp, -16
movq %rsp, %rbp
.cfi_def_cfa_register %rbp
leaq L_.str(%rip), %rdi
movb $0, %al
callq _printf
popq %rbp
retq
.cfi_endproc
## -- End function
.section __TEXT,__cstring,cstring_literals
L_.str: ## @.str
.asciz "Hello world\n"
.subsections_via_symbols
17.4. Assembling¶
gcc -c hello.s -o hello.o
ls
now we see a new file, the .o
hello.c hello.i hello.o hello.s
let’s look at it
cat hello.o
This is not machine readable, though
<__compact_unwind__LD( P?__eh_frame__TEXTH@p
h2
??
PUH??H?= ??]?Hello world
zRx
-_main_printf```
MacOS tried to help a little but it’s still not very readable.
17.5. Linking¶
Now we can link it all together; in this program there are not a lot of other depdencies, but this fills in anything from libraries and outputs an executble
gcc -o hello hello.o -lm
the -o flag specifie the name for output and -lm tells it t link from the.o file.
again we can look at the directory
ls
we have a new executable file
hello hello.c hello.i hello.o hello.s
Finally we can run our program
./hello
and see that it works!
Hello world
17.6. Putting it all together¶
We can also do all of it at once, to see how it’s different let’s clean up the directory:
rm hello.i hello.s hello.o
and now we can tell it to compile and link
gcc -Wall -g -o hello hello.c -lm
hello.c:3:1: warning: return type of 'main' is not 'int' [-Wmain-return-type]
void main () {
^
hello.c:3:1: note: change return type to 'int'
void main () {
^~~~
int
1 warning generated.
ls
hello hello.c hello.dSYM
17.7. Working with multiple files¶
nano main.c
nano help.c
cat main.c
/* Used to illustrate separate compilation.
Created: Joe Zachary, October 22, 1992
Modified:
*/
#include <stdio.h>
void main () {
int n;
printf("Please enter a small positive integer: ");
scanf("%d", &n);
printf("The sum of the first n integers is %d\n", sum(n));
printf("The product of the first n integers is %d\n", product(n));
}
cat help.c
/* Used to illustrate separate compilation
Created: Joe Zachary, October 22, 1992
Modified:
*/
/* Requires that "n" be positive. Returns the sum of the
first "n" integers. */
int sum (int n) {
int i;
int total = 0;
for (i = 1; i <= n; i++)
total += i;
return(total);
}
/* Requires that "n" be positive. Returns the product of the
first "n" integers. */
int product (int n) {
int i;
int total = 1;
for (i = 1; i <= n; i++)
total *= i;
return(total);
}
We can first compile to object the helper functions:
gcc -Wall -g -c help.c
and then main
gcc -Wall -g -c main.c
but here we get an error:
main.c:10:1: warning: return type of 'main' is not 'int' [-Wmain-return-type]
void main () {
^
main.c:10:1: note: change return type to 'int'
void main () {
^~~~
int
main.c:14:52: error: implicit declaration of function 'sum' is invalid in C99
[-Werror,-Wimplicit-function-declaration]
printf("The sum of the first n integers is %d\n", sum(n));
^
main.c:15:56: error: implicit declaration of function 'product' is invalid in C99
[-Werror,-Wimplicit-function-declaration]
printf("The product of the first n integers is %d\n", product(n));
^
1 warning and 2 errors generated.
We can get around this, by telling main about the functions by adding
int sum(int n);
int product (int n);
to the main.c
nano main.c
cat main.c
to Review what we added, we can look at it
/* Used to illustrate separate compilation.
Created: Joe Zachary, October 22, 1992
Modified:
*/
#include <stdio.h>
int sum(int n);
int product (int n);
void main () {
int n;
printf("Please enter a small positive integer: ");
scanf("%d", &n);
printf("The sum of the first n integers is %d\n", sum(n));
printf("The product of the first n integers is %d\n", product(n));
}
Now that we have added those lines, we can build again :
gcc -Wall -g main.c
As before we get the warning, but we also get an error.
main.c:13:1: warning: return type of 'main' is not 'int' [-Wmain-return-type]
void main () {
^
main.c:13:1: note: change return type to 'int'
void main () {
^~~~
int
1 warning generated.
Undefined symbols for architecture x86_64:
"_product", referenced from:
_main in main-aaba11.o
"_sum", referenced from:
_main in main-aaba11.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
Since the we got a linker error, but we didn’t intend to link, we know that we ran the command incorrectly by adding the -c option we can get it to compile and produce the object file.
gcc -Wall -g -c main.c
we now get only the warning as before
main.c:13:1: warning: return type of 'main' is not 'int' [-Wmain-return-type]
void main () {
^
main.c:13:1: note: change return type to 'int'
void main () {
^~~~
int
1 warning generated.
We can again see what happened
ls
Now we have the .o file for main
hello hello.dSYM help.o main.o
hello.c help.c main.c
We can link everythng togther, finally by passing it both object files.
gcc -o demo main.o help.o -lm
Now we see what is there
ls
and we see tht there is a new file, the executable named demo
demo hello.c help.c main.c
hello hello.dSYM help.o main.o
Now we can run our program
./demo
and we see:
Please enter a small positive integer: 4
The sum of the first n integers is 10
The product of the first n integers is 24
it works!
17.8. Prepare for next class¶
Practice using gcc. Repeat steps we did in class, change the order of parameters. Then in
gcctips.mdsummarize what you learned as a list of tips and reminders on what the parameters do/why/when you would need them (or not). (to reinforce what we learned)Create
operators.mdand make some notes about what you know about operators. What kinds of operators are you familiar with? Which have you seen in programming? math?Add the following to your kwl chart
|compiling | _ | _ | _ | | linking | _ | _ | _ | | building | _ | _ | _ | | machine representation | _ | _ | _ | | integers | _ | _ | _ | | floating point | _ | _ | _ |
17.9. More Practice¶
(priority) Write two short programs that do the same thing in different ways and compile them both to assembly (eg using a for vs while loop to sum numbers up to a number). Check the assembly to see if they produce the same thing or if it's different.
Add (or link) a glossary term, cheatsheet tip, or historical context to note on the course website.
17.10. Questions After Class¶
17.10.1. In the .o files, how does the computer interpret the gibberish? What does it actually do?¶
This is machine code, it is binary that is designed for your hardware to interpret as instructions.
When we display it to the terminal, your computer tries to interpret that binary as text, so it ends up as weird characters mostly.
17.10.2. what flags are order sensitive when compiling in C?¶
This is a practice task to try out.
17.10.3. how does the -g flag work for all debuggers¶
the -g option leaves additional information in the object file as informtion for the debugger to use.
17.10.4. When would there be a time where you would have to look in a lower-level file (for instance, maybe something can be fixed only by going into the assembly or object code?)¶
The object file is specifically not human readable, you would never really look at it. The advantage of having it is so that you can only re-compile some parts of the code when you make small changes.
You might need to look at the assembly if you are working on very low level code, like a driver that helps a peripheral talk to the computer.
17.10.5. Why does Apple try to make the object file make sense?¶
Have not yet found this answer