5dd0c6e3c0
By using the kernel "nolibc" header to avoid requiring a C library, we can bring the initramfs size to around 4k This does involve a tiny bit of inline mips assembly which I'm not sure about. gcc seems unwilling to generate the code to load $gp at function entry of main(), so we do it by hand - but I'd rather find out why gcc doesn't.
87 lines
1.8 KiB
C
87 lines
1.8 KiB
C
#ifdef USE_LIBC
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#include <string.h>
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#include <unistd.h>
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#include <sys/mount.h>
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#include <sys/wait.h>
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#include <string.h>
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#else
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#include <nolibc.h>
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#endif
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#include <asm/setup.h>
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#define ERR(x) write(2, x, strlen(x))
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#define AVER(c) do { if(c < 0) ERR("failed: " #c); } while(0)
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static int begins_with(char * str, char * prefix)
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{
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while(*prefix) {
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if(*str == '\0') return 0;
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if(*str != *prefix) return 0;
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str++;
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prefix++;
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}
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return 1;
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}
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static void fork_exec(char * command, char *args[])
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{
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int fork_pid = fork();
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AVER(fork_pid);
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if(fork_pid > 0)
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wait(NULL);
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else
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AVER(execve(command, args, NULL));
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}
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char banner[] = "Running pre-init...\n";
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char buf[COMMAND_LINE_SIZE];
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int main(int argc, char *argv[], char *envp[])
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{
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asm("la $gp, _gp\nsw $gp,16($sp)");
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char *rootdevice = 0;
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char *p = buf;
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write(1, banner, strlen(banner));
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mount("none", "/proc", "proc", 0, NULL);
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int cmdline = open("/proc/cmdline", O_RDONLY, 0);
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if(cmdline>=0) {
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int len = read(cmdline, buf, sizeof buf - 1);
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buf[len]='\0';
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write(1, "cmdline ", 8);
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write(1, buf, len);
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};
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while(*p) {
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if(begins_with(p, "root=")) {
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rootdevice = p + 5;
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while(*p && (*p != ' ')) p++;
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*p= '\0';
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}
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while(*p && (*p != ' ')) p++;
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p++;
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}
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if(rootdevice) {
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write(1, "rootdevice ", 11);
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write(1, rootdevice, strlen(rootdevice));
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write(1, "\n", 1);
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AVER(mount(rootdevice, "/target/persist", "jffs2", 0, NULL));
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AVER(mount("/target/persist/nix", "/target/nix",
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"bind", MS_BIND, NULL));
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char *exec_args[] = { "activate", "/target" };
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fork_exec("/target/persist/activate", exec_args);
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AVER(chdir("/target"));
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AVER(mount("/target", "/", "bind", MS_BIND | MS_REC, NULL));
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AVER(chroot("."));
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argv[0] = "init";
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argv[1] = NULL;
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AVER(execve("/persist/init", argv, envp));
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}
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}
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