[net-next,4/4] filter: add minimal BPF JIT emitted image disassembler

diff --git a/scripts/bpf_jit_disasm.c b/scripts/bpf_jit_disasm.c
new file mode 100644
index 0000000..1fe9fb5
--- /dev/null
+++ b/scripts/bpf_jit_disasm.c
@@ -0,0 +1,216 @@ 
+/*
+ * Minimal BPF JIT image disassembler
+ *
+ * Disassembles BPF JIT compiler emitted opcodes back to asm insn's for
+ * debugging or verification purposes.
+ *
+ * There is no Makefile. Compile with
+ *
+ *   `gcc -Wall -O2 bpf_jit_disasm.c -o bpf_jit_disasm -lopcodes -lbfd -ldl`
+ *
+ * or similar.
+ *
+ * To get the disassembly of the JIT code, do the following:
+ *
+ *  1) `echo 2 > /proc/sys/net/core/bpf_jit_enable`
+ *  2) Load a BPF filter (e.g. `tcpdump -p -n -s 0 -i eth1 host 192.168.20.0/24`)
+ *  3) Run e.g. `./bpf_jit_disasm -o` to read out the last JIT code
+ *
+ * Copyright 2013 Daniel Borkmann <borkmann@redhat.com>
+ * Licensed under the GNU General Public License, version 2.0 (GPLv2)
+ */
+
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <assert.h>
+#include <unistd.h>
+#include <string.h>
+#include <bfd.h>
+#include <dis-asm.h>
+#include <sys/klog.h>
+#include <sys/types.h>
+#include <regex.h>
+
+#define VERSION_STRING	"1.0"
+
+static void get_exec_path(char *tpath, size_t size)
+{
+	char *path;
+	ssize_t len;
+
+	snprintf(tpath, size, "/proc/%d/exe", (int) getpid());
+	tpath[size - 1] = 0;
+
+	path = strdup(tpath);
+	assert(path);
+
+	len = readlink(path, tpath, size);
+	tpath[len] = 0;
+
+	free(path);
+}
+
+static void get_asm_insns(uint8_t *image, size_t len, unsigned long base,
+			  int opcodes)
+{
+	int count, i, pc = 0;
+	char tpath[256];
+	struct disassemble_info info;
+	disassembler_ftype disassemble;
+	bfd *bfdf;
+
+	memset(tpath, 0, sizeof(tpath));
+	get_exec_path(tpath, sizeof(tpath));
+
+	bfdf = bfd_openr(tpath, NULL);
+	assert(bfdf);
+	assert(bfd_check_format(bfdf, bfd_object));
+
+	init_disassemble_info(&info, stdout, (fprintf_ftype) fprintf);
+	info.arch = bfd_get_arch(bfdf);
+	info.mach = bfd_get_mach(bfdf);
+	info.buffer = image;
+	info.buffer_length = len;
+
+	disassemble_init_for_target(&info);
+
+	disassemble = disassembler(bfdf);
+	assert(disassemble);
+
+	do {
+		printf("%4x:\t", pc);
+
+		count = disassemble(pc, &info);
+
+		if (opcodes) {
+			printf("\n\t");
+			for (i = 0; i < count; ++i)
+				printf("%02x ", (uint8_t) image[pc + i]);
+		}
+		printf("\n");
+
+		pc += count;
+	} while(count > 0 && pc < len);
+
+	bfd_close(bfdf);
+}
+
+static char *get_klog_buff(int *klen)
+{
+	int ret, len = klogctl(10, NULL, 0);
+	char *buff = malloc(len);
+
+	assert(buff && klen);
+	ret = klogctl(3, buff, len);
+	assert(ret >= 0);
+	*klen = ret;
+
+	return buff;
+}
+
+static void put_klog_buff(char *buff)
+{
+	free(buff);
+}
+
+static int get_last_jit_image(char *haystack, size_t hlen,
+			      uint8_t *image, size_t ilen,
+			      unsigned long *base)
+{
+	char *ptr, *pptr, *tmp;
+	off_t off = 0;
+	int ret, flen, proglen, pass, ulen = 0;
+	regmatch_t pmatch[1];
+	regex_t regex;
+
+	if (hlen == 0)
+		return 0;
+
+	ret = regcomp(&regex, "flen=[[:alnum:]]+ proglen=[[:digit:]]+ "
+		      "pass=[[:digit:]]+ image=[[:xdigit:]]+", REG_EXTENDED);
+	assert(ret == 0);
+
+	ptr = haystack;
+	while (1) {
+		ret = regexec(&regex, ptr, 1, pmatch, 0);
+		if (ret == 0) {
+			ptr += pmatch[0].rm_eo;
+			off += pmatch[0].rm_eo;
+			assert(off < hlen);
+		} else
+			break;
+	}
+
+	ptr = haystack + off - (pmatch[0].rm_eo - pmatch[0].rm_so);
+	ret = sscanf(ptr, "flen=%d proglen=%d pass=%d image=%lx",
+		     &flen, &proglen, &pass, base);
+	if (ret != 4)
+		return 0;
+
+	tmp = ptr = haystack + off;
+	while ((ptr = strtok(tmp, "\n")) != NULL && ulen < ilen) {
+		tmp = NULL;
+		if (!strstr(ptr, "JIT code"))
+			continue;
+		pptr = ptr;
+		while ((ptr = strstr(pptr, ":")))
+			pptr = ptr + 1;
+		ptr = pptr;
+		do {
+			image[ulen++] = (uint8_t) strtoul(pptr, &pptr, 16);
+			if (ptr == pptr || ulen >= ilen) {
+				ulen--;
+				break;
+			}
+			ptr = pptr;
+		} while (1);
+	}
+
+	assert(ulen == proglen);
+	printf("%d bytes emitted from JIT compiler (pass:%d, flen:%d)\n",
+	       proglen, pass, flen);
+	printf("%lx + <x>:\n", *base);
+
+	regfree(&regex);
+	return ulen;
+}
+
+static void help(void)
+{
+	printf("Usage: bpf_jit_disasm [-ohv]\n");
+	printf("Version %s, written by Daniel Borkmann <borkmann@redhat.com>\n",
+	       VERSION_STRING);
+	printf("  -o                             Include opcodes in output\n");
+	printf("  -h|-v                          Show help/version\n");
+	exit(0);
+}
+
+int main(int argc, char **argv)
+{
+	int len, klen, opcodes = 0;
+	char *kbuff;
+	unsigned long base;
+	uint8_t image[4096];
+
+	if (argc > 1) {
+		if (!strncmp("-o", argv[argc - 1], 2))
+			opcodes = 1;
+		if (!strncmp("-h", argv[argc - 1], 2) ||
+		    !strncmp("-v", argv[argc - 1], 2))
+			help();
+	}
+
+	bfd_init();
+	memset(image, 0, sizeof(image));
+
+	kbuff = get_klog_buff(&klen);
+
+	len = get_last_jit_image(kbuff, klen, image, sizeof(image), &base);
+	if (len > 0 && base > 0)
+		get_asm_insns(image, len, base, opcodes);
+
+	put_klog_buff(kbuff);
+
+	return 0;
+}