toaruos/kernel/core/elf.c

/*
 * ELF Static Executable Loader
 *
 * Part of the ToAru OS Kernel
 * (C) 2011 Kevin Lange
 * Released under the terms of the NCSA License, see the included
 * README file for further information.
 */

#include <system.h>
#include <fs.h>
#include <elf.h>

/**
 * Load and execute a static ELF binary.
 *
 * We make one assumption on the location the binary expects to be loaded
 * at: that it be outside of the kernel memory space.
 *
 * Arguments are passed to the stack of the user application so that they
 * can be read properly.
 *
 * TODO: Environment variables should be loaded somewhere.
 * TODO: Keep track of file descriptors so we can do open/read/write/close
 *
 * HACK: ELF verification isn't complete.
 *
 * @param path Path to the executable to attempt to execute.
 * @param argc Number of arguments (because I'm not counting for you)
 * @param argv Pointer to a string of arguments
 */
int
exec(
		char *  path, /* Path to the executable to run */
		int     argc, /* Argument count (ie, /bin/echo hello world = 3) */
		char ** argv  /* Argument strings (including executable path) */
	) {
	/* This is technically system(), so we're forking */
	int child = fork();
	if (child == 0) {
		/* Open the file */
		fs_node_t * file = kopen(path,0);
		if (!file) {
			/* Command not found */
			kexit(127);
		}
		/* Read in the binary contents */
		Elf32_Header * header = (Elf32_Header *)malloc(file->length + 100);
		read_fs(file, 0, file->length, (uint8_t *)header);

		/* Alright, we've read the binary, time to load the loadable sections */
		/* Verify the magic */
		if (	header->e_ident[0] != ELFMAG0 ||
				header->e_ident[1] != ELFMAG1 ||
				header->e_ident[2] != ELFMAG2 ||
				header->e_ident[3] != ELFMAG3) {
			/* What? This isn't an ELF... */
			kprintf("Fatal: Not a valid ELF executable.\n");
			free(header);
			close_fs(file);
			kexit(127);
		}

		/* Load the loadable segments from the binary */
		for (uintptr_t x = 0; x < header->e_shentsize * header->e_shnum; x += header->e_shentsize) {
			/* read a section header */
			Elf32_Shdr * shdr = (Elf32_Shdr *)((uintptr_t)header + (header->e_shoff + x));
			if (shdr->sh_addr) {
				/* If this is a loadable section, load it up. */
				if (shdr->sh_addr < current_task->entry) {
					/* If this is the lowest entry point, store it for memory reasons */
					current_task->entry = shdr->sh_addr;
				}
				if (shdr->sh_addr + shdr->sh_size - current_task->entry > current_task->image_size) {
					/* We also store the total size of the memory region used by the application */
					current_task->image_size = shdr->sh_addr + shdr->sh_size - current_task->entry;
				}
				for (uintptr_t i = 0; i < shdr->sh_size; i += 0x1000) {
					/* This doesn't care if we already allocated this page */
					alloc_frame(get_page(shdr->sh_addr + i, 1, current_directory), 0, 1);
				}
				/* Copy the section into memory */
				memcpy((void *)(shdr->sh_addr), (void *)((uintptr_t)header + shdr->sh_offset), shdr->sh_size);
			}
		}

		/* Store the entry point to the code segment */
		uintptr_t entry = (uintptr_t)header->e_entry;

		/* Free the space we used for the ELF headers and files */
		free(header);
		close_fs(file);

		/* Go go go */
		enter_user_jmp(entry, argc, argv);

		/* We should never reach this code */
		kexit(0x5ADFACE);
	} else {
		/* We are emulating system(), so we need to wait for the child
		 * application to exit before we can continue. */
		/* Get the child task. */
		task_t * volatile child_task = gettask(child);
		/* If the child task doesn't exist, bail */
		if (!child_task) return -1;
		/* Wait until it finishes (this is stupidly memory intensive,
		 * but we haven't actually implemented wait() yet, so there's
		 * not all that much we can do right now. */
		while (child_task->finished == 0) {
			if (child_task->finished != 0) break;
		}
		/* Grab the child's return value */
		return child_task->retval;
	}
	/* Something went terribly wrong. */
	return -1;
}

/*
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 */