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// SPDX-License-Identifier: BSL-1.0
// compile with: gcc -fno-asynchronous-unwind-tables -fno-ident -nostdlib -ffreestanding -static -Os -fvisibility=hidden -std=gnu11 ttyrescue_nolibc.c -o ttyrescue_nolibc
// strip: strip --strip-all --remove-section=.comment --remove-section=.note --remove-section=.eh_frame_hdr --remove-section=.eh_frame --remove-section=.note.gnu.gold-version ttyrescue_nolibc
#include <poll.h>
#include <sys/mman.h>
#include <sys/ioctl.h>
#include <termios.h>
static int sys_errno;
#define SYS_ERRNO sys_errno
#include "third-party/linux_syscall_support.h"
// hopefully just intrinsics
#include <stdatomic.h>
#ifndef nullptr
#define nullptr ((void*)0)
#endif
static inline pid_t sysx_tcgetpgrp(int fd) {
int res;
if (sys_ioctl(fd, TIOCGPGRP, &res) < 0) {
return -1;
}
return res;
}
#if defined(__mips__)
#define kernelx_NCCS 23
#elif defined(__sparc__)
#define kernelx_NCCS 17
#else
#define kernelx_NCCS 19
#endif
#if defined(__alpha__) || defined(__powerpc64__) || defined(__powerpc__)
struct kernelx_termios {
unsigned int c_iflag;
unsigned int c_oflag;
unsigned int c_cflag;
unsigned int c_lflag;
unsigned char c_cc[kernelx_NCCS];
unsigned char c_line;
unsigned int c_ispeed;
unsigned int c_ospeed;
};
#else
struct kernelx_termios {
unsigned int c_iflag;
unsigned int c_oflag;
unsigned int c_cflag;
unsigned int c_lflag;
unsigned char c_line;
unsigned char c_cc[kernelx_NCCS];
};
#endif
static inline int sysx_tcgetattr(int fd, struct kernelx_termios *attr) {
return sys_ioctl(fd, TCGETS, attr);
}
static inline pid_t sysx_tcsetattr_flush(int fd, struct kernelx_termios *attr) {
return sys_ioctl(fd, TCSETSF, attr);
}
int x_strlen(const char *s) {
int len = 0;
while (*s) {
len++;
s++;
}
return len;
}
void *memset(void *s, int c, size_t n) {
for (size_t i = 0; i < n; i++) {
((unsigned char*)s)[i] = c;
}
return s;
}
static void output(const char *s) {
sys_write(2, s, x_strlen(s));
}
#define TTYRESCUE_FLAG_ATTACHED (1 << 0)
#define TTYRESCUE_FLAG_TERMIOS_SET (1 << 1)
struct termpaint_ipcseg {
atomic_int active;
atomic_int flags;
long termios_iflag;
long termios_oflag;
long termios_lflag;
long termios_vintr;
long termios_vmin;
long termios_vquit;
long termios_vstart;
long termios_vstop;
long termios_vsusp;
long termios_vtime;
};
int _start(int argc, char** argv) {
(void) argc; (void) argv;
struct termpaint_ipcseg *ctlseg = sys_mmap(0, 8048, PROT_READ | PROT_WRITE, MAP_SHARED, 3, 0);
sys_close(3);
if (ctlseg == MAP_FAILED) {
output("ttyrescue: mmap failed. Abort.\n");
sys_exit_group(1);
}
atomic_fetch_or(&ctlseg->flags, TTYRESCUE_FLAG_ATTACHED);
struct kernel_sigset_t fullset;
sys_sigfillset(&fullset);
sys_sigprocmask(SIG_BLOCK, &fullset, NULL);
struct kernel_pollfd fds[1] = { { .fd = 0, .events = POLLIN } };
while (1) {
char buf[10];
ssize_t retval;
do {
retval = sys_poll(fds, 1, -1);
} while (retval == -EINTR);
if (retval < 0) {
sys_exit_group(0);
}
retval = sys_read(0, buf, 10);
if (retval == 0) {
// parent crashed
int offset = atomic_load(&ctlseg->active);
if (offset) {
output((char*)ctlseg + offset);
}
if (atomic_load(&ctlseg->flags) & TTYRESCUE_FLAG_TERMIOS_SET) {
if (sysx_tcgetpgrp(2) == sys_getpgrp()) {
struct kernelx_termios tattr;
sysx_tcgetattr(2, &tattr);
tattr.c_iflag = (unsigned int)ctlseg->termios_iflag;
tattr.c_oflag = (unsigned int)ctlseg->termios_oflag;
tattr.c_lflag = (unsigned int)ctlseg->termios_lflag;
tattr.c_cc[VINTR] = (unsigned char)ctlseg->termios_vintr;
tattr.c_cc[VMIN] = (unsigned char)ctlseg->termios_vmin;
tattr.c_cc[VQUIT] = (unsigned char)ctlseg->termios_vquit;
tattr.c_cc[VSTART] = (unsigned char)ctlseg->termios_vstart;
tattr.c_cc[VSTOP] = (unsigned char)ctlseg->termios_vstop;
tattr.c_cc[VSUSP] = (unsigned char)ctlseg->termios_vsusp;
tattr.c_cc[VTIME] = (unsigned char)ctlseg->termios_vtime;
sysx_tcsetattr_flush(2, &tattr);
}
}
sys_exit_group(0);
}
if (retval > 0) {
// clean close of parent
sys_exit_group(0);
}
}
sys_exit_group(0);
}
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