syscalls needed for doom (tell/eof/draw_fb) + minor fixes, compiler shut up etc

This commit is contained in:
2026-05-10 21:25:41 +02:00
parent 22f20d47ad
commit 18ab2c7628
12 changed files with 507 additions and 169 deletions
+1 -9
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@@ -41,12 +41,4 @@ The recommended hardware to run PepperOS is the following:
## III. Syscall table
The syscall interface in the Pepper kernel uses the System V ABI convention for argument order.
It vaguely mimics Unix-like systems.
Name | Number (%rax) | arg0 (%rdi) | arg1 (%rsi) | arg2 (%rdx) |
|---|---|---|---|---|
| sys_read | 0 | unsigned int fd | char* buf | size_t count |
| sys_write | 1 | unsigned int fd | const char* buf | size_t count |
| sys_open | 2 | const char* filename | int flags | |
| sys_close | 3 | unsigned int fd | | |
| sys_exit | 60 | int error_code | | |
It vaguely mimics Unix-like systems. You will find it in [SYSCALLS.md](SYSCALLS.md).
+2
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@@ -19,6 +19,8 @@ Of course, all of the freestanding headers are available:
Also available is the `<syscall.h>` header that gives access to low-level system call interface, notably the `syscallX` function family, X being the amount of arguments to use.
(TODO: put the other headers here once libc is more complete)
## 1. Write the source code
PepperOS is able to run programs written in x86 assembly, and C programs.
+11
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@@ -0,0 +1,11 @@
# Pepper kernel system call table
The following table contains all of the system calls supported by PepperOS, as well as their arguments. The explanation for what every system call does is available as a comment above each function in corresponding files in the `src/syscall` folder.
Name | Number (%rax) | arg0 (%rdi) | arg1 (%rsi) | arg2 (%rdx) |
|---|---|---|---|---|
| sys_read | 0 | unsigned int fd | char* buf | size_t count |
| sys_write | 1 | unsigned int fd | const char* buf | size_t count |
| sys_open | 2 | const char* filename | int flags | |
| sys_close | 3 | unsigned int fd | | |
| sys_exit | 60 | int error_code | | |
+6
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@@ -15,4 +15,10 @@ int tar_exists(const char* filename);
int tar_read(char* filename, char* out, int count, int offset);
void tar_list();
enum Seek {
SEEK_SET,
SEEK_CUR,
SEEK_END
};
#endif
+1
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@@ -9,6 +9,7 @@
#include "limine.h"
// Not in POSIX order.
enum ErrorCodes {
ENOMEM, // No memory
EIO, // Input/output error
-160
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@@ -1,160 +0,0 @@
/*
* @author xamidev <xamidev@riseup.net>
* @brief System call handling
* @license GPL-3.0-only
*/
#include "config.h"
#include "sched/scheduler.h"
#include <arch/x86.h>
#include <kernel.h>
#include <stddef.h>
#include <io/term/term.h>
#include <sched/process.h>
#include <io/kbd/ps2.h>
#include <fs/initfs.h>
#include <string/string.h>
extern struct process* current_process;
// Return fd on success, -errno on error
int sys_open(const char* filename, int flags)
{
if (tar_exists(filename) < 0) {
return -ENOENT; // file doesn't exist..
}
// file exists here!
if (current_process->next_free_fd >= FDT_MAX) {
return -EMFILE;
}
int fd = current_process->next_free_fd++;
current_process->fdt[fd].fd = fd;
current_process->fdt[fd].open = true;
current_process->fdt[fd].cursor = 0;
strncpy(current_process->fdt[fd].filename, filename, PROCESS_NAME_MAX - 1);
return fd;
}
// Return 0 on success, -EBADFD if invalid FD
int sys_close(int fd)
{
if (fd < 0 || fd >= FDT_MAX) {
return -EBADFD;
}
if (!current_process->fdt[fd].open) {
return -EBADFD; // FD not opened in the first place
}
current_process->fdt[fd].open = false;
current_process->fdt[fd].filename[0] = '\0';
current_process->fdt[fd].cursor = 0;
return 0;
}
// Should return the number of bytes read
int sys_read(unsigned int fd, char* buf, size_t count)
{
size_t i;
switch (fd) {
case 0: //read from stdin (keyboard)
for (i=0; i<count; i++) {
buf[i] = keyboard_getchar();
}
return i;
case 1: // from stdout
case 2: // from stderr
return -EBADFD;
default: // from an open file?
if (current_process->fdt[fd].open == false) {
return -EBADFD; // File descriptor wasn't open
}
// Here fd refers to a valid opened file..
int sz = tar_read(current_process->fdt[fd].filename, buf, count,
current_process->fdt[fd].cursor);
if (sz == 0) {
return -ENOENT;
} else {
current_process->fdt[fd].cursor += sz;
return sz;
}
}
return -EBADFD;
}
// TODO: Should have a return value: number of bytes written on success, -1 on error (errno set)
int sys_write(unsigned int fd, const char* buf, size_t count)
{
switch (fd) {
case 1: //stdout
case 2: //stderr
for (size_t i=0; i<count; i++) {
internal_putc(buf[i], NULL);
}
return count;
default:
return -EBADFD;
}
}
int sys_exit(int error_code)
{
current_process->status = DEAD;
DEBUG("(pid=%u, name=%s)", current_process->pid, current_process->name);
return error_code;
}
/*
* syscall_handler - System call dispatcher
* @regs: CPU state
*
* This function is called from the interrupt dispatcher,
* when an interrupt 0x80 is emitted from userland.
*
* It switches control to the syscall number provided
* in %rax.
*
* We try to follow the System V convention here:
* - syscall number in %rax
* - args in %rdi, %rsi, %rdx, %r10, %r8, %r9
* - return value (if any) in %rax
*
* Return:
* <regs> - CPU state after system call
*/
struct cpu_status* syscall_handler(struct cpu_status* regs)
{
switch (regs->rax)
{
case 0:
DEBUG("sys_read(fd=%u, buf=%p, count=%u)", regs->rdi, regs->rsi, regs->rdx);
regs->rax = sys_read(regs->rdi, (char*)regs->rsi, regs->rdx);
break;
case 1:
DEBUG("sys_write(fd=%u, buf=%p, count=%u)", regs->rdi, regs->rsi, regs->rdx);
regs->rax = sys_write(regs->rdi, (char*)regs->rsi, regs->rdx);
break;
case 2:
DEBUG("sys_open(filename=%s, flags=%u)", regs->rdi, regs->rsi);
regs->rax = sys_open((const char*)regs->rdi, regs->rsi);
break;
case 3:
DEBUG("sys_close(fd=%u)", regs->rdi);
regs->rax = sys_close(regs->rdi);
break;
case 60:
DEBUG("sys_exit(error_code=%d)", regs->rdi);
regs->rax = sys_exit(regs->rdi);
break;
default:
DEBUG("Bad syscall! (rax=%p, rdi=%p, rsi=%p, rdx=%p)",
regs->rax, regs->rdi, regs->rsi, regs->rdx);
regs->rax = 0xbad515ca11;
break;
}
DEBUG("returned rax=%p (%u)", regs->rax, regs->rax);
return regs;
}
+1
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@@ -82,6 +82,7 @@ void kill()
*/
void pedicel_main(void* arg)
{
(void)arg;
printf("Welcome to the kernel shell!\r\nType 'help' for a list of commands.\r\n");
for (;;) {
+1
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@@ -73,6 +73,7 @@ struct process* idle_proc;
void idle_main(void* arg)
{
(void)arg;
for (;;) {
asm("hlt");
}
+252
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@@ -0,0 +1,252 @@
/*
* @author xamidev <xamidev@riseup.net>
* @brief File-related system calls
* @license GPL-3.0-only
*/
#include <stddef.h>
#include <kernel.h>
#include <config.h>
#include <sched/process.h>
#include <string/string.h>
#include <fs/initfs.h>
#include <io/kbd/ps2.h>
extern struct process* current_process;
/*
* normalize_path - remove leading slashes from a path
* @path: path to normalize
*
* Return:
* %path - normalized path
* %NULL - if bad argument
*/
static const char* normalize_path(const char* path)
{
if (!path) return NULL;
while (*path == '/') {
path++;
}
return path;
}
/*
* sys_open - Open a file
* @filename: Absolute path to file
* @flags: (Not implemented)
*
* This system call opens a file in read-only mode,
* because of the TAR filesystem.
*
* Return:
* %fd - file descriptor refering to file
* On error, a negative number representing the error code is returned.
*/
int sys_open(const char* filename, int flags)
{
// TODO: support flags (right now everything is read only, O_RDONLY)
(void)flags; // gcc shut up
const char* path = normalize_path(filename);
if (tar_exists(path) < 0) {
return -ENOENT; // file doesn't exist..
}
// file exists here!
if (current_process->next_free_fd >= FDT_MAX) {
return -EMFILE;
}
int fd = current_process->next_free_fd++;
current_process->fdt[fd].fd = fd;
current_process->fdt[fd].open = true;
current_process->fdt[fd].cursor = 0;
strncpy(current_process->fdt[fd].filename, path, PROCESS_NAME_MAX - 1);
return fd;
}
/*
* sys_close - Close a file
* @fd: file descriptor
*
* This system call closes the file referred to by
* the file descriptor @fd.
*
* Return:
* %0 - file closed
* %-EBADFD - bad file descriptor
*/
int sys_close(int fd)
{
if (fd < 0 || fd >= FDT_MAX) {
return -EBADFD;
}
if (!current_process->fdt[fd].open) {
return -EBADFD; // FD not opened in the first place
}
current_process->fdt[fd].open = false;
current_process->fdt[fd].filename[0] = '\0';
current_process->fdt[fd].cursor = 0;
return 0;
}
/*
* sys_lseek - reposition file cursor
* @fd: file descriptor referring to file
* @offset: byte amount to be used according to @whence
* @whence: resposition directive
*
* This system call repositions the cursor for @fd by @offset,
* from somewhere in the file, depending on the value of @whence:
* SEEK_SET (0) -> from the beginning
* SEEK_CUR (1) -> from the actual value of the cursor
* SEEK_END (2) -> from the end of the file
*
* Return:
* %new_cursor - the new cursor value
* On error, a negative value corresponding to an error code is returned.
*/
int sys_lseek(int fd, int offset, int whence)
{
if (fd < 0 || fd >= FDT_MAX) {
return -EBADFD;
}
if (!current_process->fdt[fd].open) {
return -EBADFD;
}
int filesize = tar_exists(current_process->fdt[fd].filename);
if (filesize < 0) {
return -ENOENT;
}
int cursor = current_process->fdt[fd].cursor;
int base;
switch (whence) {
case SEEK_SET: base = 0; break;
case SEEK_CUR: base = cursor; break;
case SEEK_END: base = filesize; break;
default: return -EINVAL;
}
int new_cursor = base + offset;
if (new_cursor < 0) new_cursor = 0;
if (new_cursor > filesize) new_cursor = filesize;
current_process->fdt[fd].cursor = new_cursor;
return new_cursor;
}
/*
* sys_tell - Get cursor position for a file
* @fd: file descriptor to use
*
* Return:
* %cursor - cursor position of the file descriptor
* On error, a negative value with the corresponding error code is set.
*/
int sys_tell(int fd)
{
if (fd < 0 || fd >= FDT_MAX) {
return -EBADFD;
}
if (!current_process->fdt[fd].open) {
return -EBADFD;
}
return current_process->fdt[fd].cursor;
}
/*
* sys_eof - Are we at the end of the file yet?
* @fd: file descriptor to use
*
* This function determines if the cursor for the
* file descriptor @fd is at or past the end of
* the file it refers to.
*
* Return:
* %>0 - we are at or past EOF
* %0 - not yet (still have bytes to read)
*/
int sys_eof(int fd)
{
if (fd < 0 || fd >= FDT_MAX) {
return -EBADFD;
}
if (!current_process->fdt[fd].open) {
return -EBADFD;
}
int filesize = tar_exists(current_process->fdt[fd].filename);
if (filesize < 0) {
return -ENOENT;
}
return current_process->fdt[fd].cursor >= (uint64_t)filesize;
}
/*
* sys_read - read from an open file
* @fd: file descriptor to use
* @buf: out buffer for read data
* @count: amount of bytes to read
*
* Return:
* %sz - amount of bytes read (on success)
* On error, a negative value with an error code is returned.
*/
int sys_read(unsigned int fd, char* buf, size_t count)
{
size_t i;
switch (fd) {
case 0: //read from stdin (keyboard)
for (i=0; i<count; i++) {
buf[i] = keyboard_getchar();
}
return i;
case 1: // from stdout
case 2: // from stderr
return -EBADFD;
default: // from an open file?
if (current_process->fdt[fd].open == false) {
return -EBADFD; // File descriptor wasn't open
}
// Here fd refers to a valid opened file..
int sz = tar_read(current_process->fdt[fd].filename, buf, count,
current_process->fdt[fd].cursor);
if (sz == 0) {
return -ENOENT;
} else {
current_process->fdt[fd].cursor += sz;
return sz;
}
}
return -EBADFD;
}
/*
* sys_write - write to a file
* @fd: file descriptor to write to
* @buf: buffer of bytes to write
* @count: number of bytes to write
*
* Return:
* %count - number of bytes written
* On error, a negative value with corresponding error code is returned.
*/
int sys_write(unsigned int fd, const char* buf, size_t count)
{
switch (fd) {
case 1: //stdout
case 2: //stderr
for (size_t i=0; i<count; i++) {
internal_putc(buf[i], NULL);
}
return count;
default:
return -EBADFD;
}
}
+28
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@@ -0,0 +1,28 @@
/*
* @author xamidev <xamidev@riseup.net>
* @brief Process-wide system calls
* @license GPL-3.0-only
*/
#include <kernel.h>
#include <sched/process.h>
extern struct process* current_process;
/*
* sys_exit - Terminate the current process
* @error_code: error code to return
*
* This system call exits the running process. Be aware that
* it does nothing except that. All resources are supposed to
* be cleaned up before calling this.
*
* Return:
* %error_code - the error code to return
*/
int sys_exit(int error_code)
{
current_process->status = DEAD;
DEBUG("(pid=%u, name=%s)", current_process->pid, current_process->name);
return error_code;
}
+105
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@@ -0,0 +1,105 @@
/*
* @author xamidev <xamidev@riseup.net>
* @brief Screen/framebuffer system calls
* @license GPL-3.0-only
*/
// This is not part of POSIX or anything btw
#include <stdint.h>
#include <kernel.h>
extern struct boot_context boot_ctx;
/*
* pack_rbga_to_fb - Convert rgb values to rgba pixel for framebuffer
* @r: red value
* @g: green value
* @b: blue value
*
* This function uses the mask sizes and shifts of the Limine
* framebuffer to convert raw rgb values into usable pixels.
*
* Return:
* <pixel> - usable pixel
*/
static uint32_t pack_rgba_to_fb(uint8_t r, uint8_t g, uint8_t b)
{
uint32_t pixel = 0;
if (boot_ctx.fb->red_mask_size) {
pixel |= ((uint32_t)(r >> (8 - boot_ctx.fb->red_mask_size)) << boot_ctx.fb->red_mask_shift);
}
if (boot_ctx.fb->green_mask_size) {
pixel |= ((uint32_t)(g >> (8 - boot_ctx.fb->green_mask_size)) << boot_ctx.fb->green_mask_shift);
}
if (boot_ctx.fb->blue_mask_size) {
pixel |= ((uint32_t)(b >> (8 - boot_ctx.fb->blue_mask_size)) << boot_ctx.fb->blue_mask_shift);
}
return pixel;
}
/*
* sys_draw_fb - Draw a framebuffer subset
* @src: Source frame
* @width: width of the frame
* @height: height of the frame
* @channels: how many channels (RGB, RGBA)
*
* This system call draws the frame @src, having some
* @width and @height, in the top right of the Limine
* framebuffer. (Used for DOOM)
*
* Return:
* %0 - on success
* On error, a negative value with an error code is returned.
*/
int sys_draw_fb(const uint8_t* src, int width, int height, int channels)
{
if (!boot_ctx.fb || !src) {
return -EINVAL;
}
if (channels != 4 || width <= 0 || height <= 0) {
return -EINVAL;
}
if (boot_ctx.fb->bpp < 24) {
return -EIO;
}
uint32_t* dst = (uint32_t*)boot_ctx.fb->address;
uint64_t dst_w = boot_ctx.fb->width;
uint64_t dst_h = boot_ctx.fb->height;
uint64_t dst_pitch_px = boot_ctx.fb->pitch / 4;
uint64_t scale = 2;
uint64_t scaled_w = (uint64_t)width * scale;
uint64_t scaled_h = (uint64_t)height * scale;
if (scaled_w > dst_w || scaled_h > dst_h) {
return -EINVAL;
}
uint64_t dst_x = dst_w - scaled_w;
uint64_t dst_y = 0;
for (uint64_t y = 0; y < (uint64_t)height; ++y) {
const uint8_t* src_row = src + y * (uint64_t)width * 4ULL;
uint32_t* dst_row0 = dst + (dst_y + y * scale) * dst_pitch_px + dst_x;
uint32_t* dst_row1 = dst_row0 + dst_pitch_px;
for (uint64_t x = 0; x < (uint64_t)width; ++x) {
const uint8_t* p = src_row + x * 4ULL;
uint32_t pixel = pack_rgba_to_fb(p[0], p[1], p[2]);
uint64_t dx = x * scale;
// Write 2x2 block. This is because source DOOM frame (320x200)
// is quite small.
dst_row0[dx + 0] = pixel;
dst_row0[dx + 1] = pixel;
dst_row1[dx + 0] = pixel;
dst_row1[dx + 1] = pixel;
}
}
return 0;
}
+99
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@@ -0,0 +1,99 @@
/*
* @author xamidev <xamidev@riseup.net>
* @brief System call handling
* @license GPL-3.0-only
*/
#include "config.h"
#include "sched/scheduler.h"
#include <arch/x86.h>
#include <kernel.h>
#include <stddef.h>
#include <io/term/term.h>
#include <sched/process.h>
#include <io/kbd/ps2.h>
#include <fs/initfs.h>
#include <string/string.h>
#include <mem/utils.h>
extern struct process* current_process;
int sys_open(const char* filename, int flags);
int sys_close(int fd);
int sys_lseek(int fd, int offset, int whence);
int sys_tell(int fd); // needed by doom, therefore TOP PRIORITY
int sys_eof(int fd); // same
int sys_read(unsigned int fd, char* buf, size_t count);
int sys_write(unsigned int fd, const char* buf, size_t count);
int sys_exit(int error_code);
int sys_draw_fb(const uint8_t* src, int width, int height, int channels);
/*
* syscall_handler - System call dispatcher
* @regs: CPU state
*
* This function is called from the interrupt dispatcher,
* when an interrupt 0x80 is emitted from userland.
*
* It switches control to the syscall number provided
* in %rax.
*
* We try to follow the System V convention here:
* - syscall number in %rax
* - args in %rdi, %rsi, %rdx, %r10, %r8, %r9
* - return value (if any) in %rax
*
* Return:
* <regs> - CPU state after system call
*/
struct cpu_status* syscall_handler(struct cpu_status* regs)
{
switch (regs->rax)
{
case 0:
DEBUG("sys_read(fd=%u, buf=%p, count=%u)", regs->rdi, regs->rsi, regs->rdx);
regs->rax = sys_read(regs->rdi, (char*)regs->rsi, regs->rdx);
break;
case 1:
DEBUG("sys_write(fd=%u, buf=%p, count=%u)", regs->rdi, regs->rsi, regs->rdx);
regs->rax = sys_write(regs->rdi, (char*)regs->rsi, regs->rdx);
break;
case 2:
DEBUG("sys_open(filename=%s, flags=%u)", regs->rdi, regs->rsi);
regs->rax = sys_open((const char*)regs->rdi, regs->rsi);
break;
case 3:
DEBUG("sys_close(fd=%u)", regs->rdi);
regs->rax = sys_close(regs->rdi);
break;
case 8:
DEBUG("sys_lseek(fd=%u, off=%d, whence=%u)", regs->rdi, regs->rsi, regs->rdx);
regs->rax = sys_lseek(regs->rdi, regs->rsi, regs->rdx);
break;
case 9:
DEBUG("sys_tell(fd=%u)", regs->rdi);
regs->rax = sys_tell(regs->rdi);
break;
case 10:
DEBUG("sys_eof(fd=%u)", regs->rdi);
regs->rax = sys_eof(regs->rdi);
break;
case 11: // No DEBUG() here because it makes significant overhead
regs->rax = sys_draw_fb((const uint8_t*)regs->rdi, regs->rsi, regs->rdx, regs->r10);
break;
case 60:
DEBUG("sys_exit(error_code=%d)", regs->rdi);
regs->rax = sys_exit(regs->rdi);
break;
default:
DEBUG("Bad syscall! (rax=%p, rdi=%p, rsi=%p, rdx=%p)",
regs->rax, regs->rdi, regs->rsi, regs->rdx);
regs->rax = 0xbad515ca11;
break;
}
// save overhead for present_fb
//DEBUG("returned rax=%p (%u)", regs->rax, regs->rax);
return regs;
}