minimal POSIX compliant sleep

Related tags

Miscellaneous sleep
Overview

Minimal POSIX compliant sleep.

Results

Only 3 syscalls per execution

$ strace ./sleep 1
execve("./sleep", ["./sleep", "1"], 0x7ffc998d09a8 /* 40 vars */) = 0
nanosleep({tv_sec=1, tv_nsec=0}, NULL)  = 0
exit(0)                                 = ?
+++ exited with 0 +++

Compared to an empty C program compiled with gcc

$ strace ./a.out
execve("./a.out", ["./a.out"], 0x7ffe2f0aa150 /* 40 vars */) = 0
brk(NULL)                               = 0x561007006000
arch_prctl(0x3001 /* ARCH_??? */, 0x7ffeacd2dff0) = -1 EINVAL (Invalid argument)
access("/etc/ld.so.preload", R_OK)      = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=116514, ...}) = 0
mmap(NULL, 116514, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f74729a9000
close(3)                                = 0
openat(AT_FDCWD, "/usr/lib/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\220\202\2\0\0\0\0\0"..., 832) = 832
pread64(3, "\6\0\0\0\4\0\0\[email protected]\0\0\0\0\0\0\[email protected]\0\0\0\0\0\0\[email protected]\0\0\0\0\0\0\0"..., 784, 64) = 784
pread64(3, "\4\0\0\0\20\0\0\0\5\0\0\0GNU\0\2\0\0\300\4\0\0\0\3\0\0\0\0\0\0\0", 32, 848) = 32
pread64(3, "\4\0\0\0\24\0\0\0\3\0\0\0GNU\0\207\360\21\247\344\314?\306\nT\320\323\335i\16t"..., 68, 880) = 68
fstat(3, {st_mode=S_IFREG|0755, st_size=2159552, ...}) = 0
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f74729a7000
pread64(3, "\6\0\0\0\4\0\0\[email protected]\0\0\0\0\0\0\[email protected]\0\0\0\0\0\0\[email protected]\0\0\0\0\0\0\0"..., 784, 64) = 784
mmap(NULL, 1868448, PROT_READ, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f74727de000
mmap(0x7f7472804000, 1363968, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x26000) = 0x7f7472804000
mmap(0x7f7472951000, 311296, PROT_READ, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x173000) = 0x7f7472951000
mmap(0x7f747299d000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1be000) = 0x7f747299d000
mmap(0x7f74729a3000, 12960, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7f74729a3000
close(3)                                = 0
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f74727dc000
arch_prctl(ARCH_SET_FS, 0x7f74729a8540) = 0
mprotect(0x7f747299d000, 12288, PROT_READ) = 0
mprotect(0x5610050fc000, 4096, PROT_READ) = 0
mprotect(0x7f74729f2000, 4096, PROT_READ) = 0
munmap(0x7f74729a9000, 116514)          = 0
exit_group(0)                           = ?
+++ exited with 0 +++

Small binary

$ du -b ./sleep /bin/sleep ./a.out
864     ./sleep
39048   /bin/sleep             # default arch sleep binary
14184   ./a.out                # empty C program compiled with gcc

The above measurement is the apparent size, as modern file systems allocate memory in blocks of 4096 bytes, further reducing the size won't actually change the disk usage reported below.

$ du -B1 ./sleep /bin/sleep ./a.out
4096    ./sleep
40960   /bin/sleep             # default arch sleep binary
16384   ./a.out                # empty C program compiled with gcc

Compilation

Compilation dependencies:

  • gcc
  • make
make sleep

Usage

./sleep SECONDS

where SECONDS is a non negative number (e.g. 15, 12.003)

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