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1d8937d528
This change reduces the memory requirements of your APE Loader by 10x, in terms of virtual memory size, thanks to the help of alloca(). We're also now creating argument blocks with the same layout across systems.
85 lines
3.5 KiB
C
85 lines
3.5 KiB
C
#if 0
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/*─────────────────────────────────────────────────────────────────╗
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│ To the extent possible under law, Justine Tunney has waived │
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│ all copyright and related or neighboring rights to this file, │
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│ as it is written in the following disclaimers: │
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│ • http://unlicense.org/ │
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│ • http://creativecommons.org/publicdomain/zero/1.0/ │
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╚─────────────────────────────────────────────────────────────────*/
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#endif
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#include "libc/calls/calls.h"
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#include "libc/calls/struct/sigaction.h"
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#include "libc/errno.h"
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#include "libc/runtime/runtime.h"
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#include "libc/stdio/stdio.h"
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#include "libc/sysv/consts/limits.h"
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#include "libc/sysv/consts/sig.h"
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void SignalHandler(int sig) {
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// we don't need to do anything in our signal handler since the signal
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// delivery itself causes a visible state change, saying what happened
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}
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int main(int argc, char *argv[]) {
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printf("echoing stdin until ctrl+c is pressed\n");
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// you need to set your signal handler using sigaction() rather than
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// signal(), since the latter uses .sa_flags=SA_RESTART, which means
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// read will restart itself after signals, rather than raising EINTR
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sigaction(SIGINT, &(struct sigaction){.sa_handler = SignalHandler}, 0);
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for (;;) {
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// posix guarantees atomic i/o if you use pipe_buf sized buffers
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// that way we don't need to worry about things like looping and
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// we can also be assured that multiple actors wont have tearing
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char buf[PIPE_BUF];
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// read data from standard input
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//
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// since this is a blocking operation and we're not performing a
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// cpu-bound operation it is almost with absolute certainty that
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// when the ctrl-c signal gets delivered, it'll happen in read()
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//
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// it's possible to be more precise if we were building library
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// code. for example, you can block signals using sigprocmask()
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// and then use pselect() to do the waiting.
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int got = read(0, buf, sizeof(buf));
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// check if the read operation failed
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// negative one is the *only* return value to indicate errors
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if (got == -1) {
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if (errno == EINTR) {
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// a signal handler was invoked during the read operation
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// since we have only one such signal handler it's sigint
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// if we didn't have any signal handlers in our app, then
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// we wouldn't need to check this errno. using SA_RESTART
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// is another great way to avoid having to worry about it
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// however EINTR is very useful, when we choose to use it
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// the \r character is needed so when the line is printed
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// it'll overwrite the ^C that got echo'd with the ctrl-c
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printf("\rgot ctrl+c\n");
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exit(0);
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} else {
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// log it in the unlikely event something else went wrong
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perror("<stdin>");
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exit(1);
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}
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}
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// check if the user typed ctrl-d which closes the input handle
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if (!got) {
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printf("got eof\n");
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exit(0);
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}
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// relay read data to standard output
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//
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// it's usually safe to ignore the return code of write. the
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// operating system will send SIGPIPE if there's any problem
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// which kills the process by default
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write(1, buf, got);
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}
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}
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