README.md

FUSE test

$ ./elfs elfs tmp

$ ls tmp
Elf64  sections

$ ls tmp/sections
0  10  12  14  16  18  2   21  23  25  27  29  30  5  7  9
1  11  13  15  17  19  20  22  24  26  28  3   4   6  8

$ cat tmp/sections/1
.interp

elfs.c

#include <unistd.h>
#include <sys/mman.h>
#include <elf.h>
#include <fuse.h>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <fcntl.h>
#include <string.h>

static void *ptr;

static int sections;
static int bits;

#ifdef __i386__
#define BITS 32
#endif
#ifdef __x86_64__
#define BITS 64
#endif

#include "elfs_elf.c"

static int map(const char *path)
{
	struct stat st;
	int fd;

	fd = open(path, O_RDONLY);
	if (fd == -1 || fstat(fd, &st) == -1)
		return -1;

	ptr = mmap(NULL, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0);

	close(fd);

	return !!(ptr == MAP_FAILED);
}

static int init(const char *path)
{
	const char *e;

	if (map(path))
		return -1;

	e = ptr;

	/* check ELF header */
	if (memcmp(e, ELFMAG, SELFMAG))
		return -1;
	/* support 32 or 64 */
	switch (e[EI_CLASS]) {
	case ELFCLASS32:
		bits = 32;
		break;
	case ELFCLASS64:
		bits = 64;
		break;
	default:
		return -1;
	}

	return elfs_elf_init(bits);
}

static int elfs_getattr(const char *path, struct stat *st)
{
	int len = strlen("/sections");

	memset(st, 0, sizeof(struct stat));

	if (!strncmp(path, "/sections", len))
		return elfs_getattr_sections(path + len, st);

	if (!strcmp(path, "/")) {
		st->st_mode = S_IFDIR | 0755;
		st->st_nlink = 2;
		return 0;
	}

	st->st_mode = S_IFREG | 0444;
	st->st_nlink = 1;

	return 0;
}

static int elfs_readdir(const char *path, void *buf, fuse_fill_dir_t filler,
			off_t offset, struct fuse_file_info *fi)
{
	char tmp[32];
	int len = strlen("/sections");

	if (!strncmp(path, "/sections", len))
		return elfs_readdir_sections(path + len, buf, filler, offset, fi);

	if (strcmp(path, "/"))
		return -ENOENT;

	filler(buf, ".", NULL, 0);
	filler(buf, "..", NULL, 0);

	sprintf(tmp, "Elf%d", bits);
	filler(buf, tmp, NULL, 0);
	filler(buf, "sections", NULL, 0);

	return 0;
}

static int elfs_open(const char *path, struct fuse_file_info *fi)
{
	int len = strlen("/sections");
	char tmp[32];

	if (!strncmp(path, "/sections", len))
		return elfs_open_sections(path + len, fi);

	sprintf(tmp, "/Elf%d", bits);
	if (strcmp(path, tmp))
		return -ENOENT;

	if ((fi->flags & 3) != O_RDONLY)
		return -EACCES;

	return 0;
}

static int elfs_read(const char *path, char *buf, size_t size, off_t offset,
			struct fuse_file_info *fi)
{
	int len = strlen("/sections");
	char tmp[32];

	if (!strncmp(path, "/sections", len))
		return elfs_read_sections(path + len, buf, size, offset, fi);

	sprintf(tmp, "/Elf%d", bits);
	if (strcmp(path, tmp))
		return -ENOENT;

	return 0;
}

static struct fuse_operations elfs_op = {
	.getattr = elfs_getattr,
	.readdir = elfs_readdir,
	.open = elfs_open,
	.read = elfs_read,
};

int main(int argc, char **argv)
{
	struct fuse_args args = FUSE_ARGS_INIT(0, NULL);

	if (argc != 3)
		goto err;

	if (init(argv[1]))
		goto err;

	fuse_opt_add_arg(&args, argv[0]);
	fuse_opt_add_arg(&args, argv[2]);

	return fuse_main(args.argc, args.argv, &elfs_op, NULL);

err:
	fprintf(stderr, "error\n");

	return 1;
}

elfs_elf.c

#ifndef BITS
#error "No BITS"
#endif

#define STR0(x,y) x ## y
#define STR(x,y) STR0(x,y)

#define E(x) STR(STR(STR(Elf, BITS), _), x)
#define Elf_Ehdr E(Ehdr)
#define Elf_Shdr E(Shdr)

static int elfs_elf_init(int bits)
{
	Elf_Ehdr *e = ptr;

	if (bits != BITS)
		return -1;

	sections = e->e_shnum;

	return 0;
}

static int elfs_getattr_sections(const char *path, struct stat *st)
{
	if (*path == 0 || !strcmp(path, "/")) {
		st->st_mode = S_IFDIR | 0755;
		st->st_nlink = 2;
		return 0;
	}
	st->st_mode = S_IFREG | 0444;
	st->st_nlink = 1;
	st->st_size = 4096;
	return 0;
}

static int elfs_readdir_sections(const char *path, void *buf,
				fuse_fill_dir_t filler,
				off_t offset, struct fuse_file_info *fi)
{
	char tmp[64];
	int i;

	filler(buf, ".", NULL, 0);
	filler(buf, "..", NULL, 0);

	for (i = 0; i < sections; i++) {
		sprintf(tmp, "%d", i);
		filler(buf, tmp, NULL, 0);
	}

	return 0;
}

static int elfs_open_sections(const char *path, struct fuse_file_info *fi)
{
	int n = atoi(path + 1);

	if (n < 0 || sections < n)
		return -ENOENT;

	if ((fi->flags & 3) != O_RDONLY)
		return -EACCES;

	return 0;
}

static int elfs_read_sections(const char *path, char *buf, size_t size,
				off_t offset, struct fuse_file_info *fi)
{
	Elf_Ehdr *e = ptr;
	Elf_Shdr *sh = ptr + e->e_shoff;
	int stidx = e->e_shstrndx;
	int n = atoi(path + 1);
	int len;
	char tmp[4096];
	char *str;

	if (n < 0 || sections < n)
		return -ENOENT;

	str = ptr + sh[stidx].sh_offset;
	sprintf(tmp, "%s\n", str + sh[n].sh_name);
	len = strlen(tmp);

	if (offset >= len)
		return 0;

	if (offset + size > len)
		size = len - offset;

	memcpy(buf, tmp + offset, size);

	return size;
}

Makefile

all:
	gcc -Wall `pkg-config fuse --cflags --libs` -DFUSE_USE_VERSION=26 elfs.c -o elfs

clean:
	rm -f elfs