memzap

commit 83b823d88eff2d07297b655dd003bf9e2e213067
parent e13f55bfbdf51e7981d053ebbbcec3f738b6110f
Author: sin <sin@2f30.org>
Date:   Tue,  5 Mar 2013 17:51:34 +0000

memzap: Implement -s option

We can now lookup symbols in ELF files and trace them.

Diffstat:
M
commonvar.mk
 | 
2
+-
M
memzap.c
 | 
81
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++---------

2 files changed, 73 insertions(+), 10 deletions(-)
diff --git a/commonvar.mk b/commonvar.mk
@@ -3,7 +3,7 @@ PREFIX ?= /usr/local
 CC := $(CROSS_COMPILE)$(CC)
 
 CFLAGS += -g -O3 -Wall -Wextra -Wunused -DVERSION=\"$(VER)\" $(INCS)
-LDFLAGS +=
+LDFLAGS += -lelf
 
 INCS = -I/usr/local/include
 LIBS = -L/usr/local/lib
diff --git a/memzap.c b/memzap.c
@@ -1,8 +1,12 @@
 /* See LICENSE file for copyright and license details. */
 
+#include <libelf.h>
+#include <gelf.h>
+
 #include "proto.h"
 
 static int verbose = 0;
+static int fsymbol = 0;
 
 static void
 usage(const char *prog)
@@ -37,6 +41,11 @@ dump_base_image(const char *name, void *buf, size_t len)
 	close(fdmem);
 }
 
+static Elf_Scn *scn;
+static Elf_Data *edata;
+static GElf_Sym sym;
+static GElf_Shdr shdr;
+
 int
 main(int argc, char *argv[])
 {
@@ -55,6 +64,9 @@ main(int argc, char *argv[])
 	char mdiff_path[PATH_MAX - 1];
 	bool once = false;
 	uint64_t cycle = 0;
+	char *symbol = NULL, *tmp;
+	Elf *e;
+	Elf32_Word symbol_count, i;
 
 	while ((c = getopt(argc, argv, "hs:l:r:vV")) != -1) {
 		switch (c) {
@@ -74,7 +86,9 @@ main(int argc, char *argv[])
 			len = strtoul(optarg, NULL, 10);
 			break;
 		case 's':
-			errx(1, "-s option is unimplemented");
+			fsymbol = 1;
+			symbol = strdup(optarg);
+			break;
 		case '?':
 		default:
 			return 1;
@@ -88,11 +102,60 @@ main(int argc, char *argv[])
 		return 1;
 	}
 
-	if (!addr || !len)
-		errx(1, "no memory region/len specified");
+	if (fsymbol) {
+		if (addr || len) {
+			errx(1, "You can't trace both a symbol and a region/length");
+		}
+	} else {
+		if (!addr || !len) {
+			errx(1, "no memory region/len specified");
+		}
+	}
+
+	if (fsymbol) {
+		if (elf_version(EV_CURRENT) == EV_NONE)
+			errx(1, "ELF library initialization failed: %s",
+			     elf_errmsg(-1));
+
+		fd = open(*argv, O_RDONLY);
+		if (fd < 0)
+			errx(1, "%s: %s\n", *argv, strerror(errno));
+
+		e = elf_begin(fd, ELF_C_READ, NULL);
+		if (!e)
+			errx(1, "elf_begin() failed: %s",
+			     elf_errmsg(-1));
+
+		while ((scn = elf_nextscn(e, scn))) {
+			gelf_getshdr(scn, &shdr);
+			if (shdr.sh_type == SHT_SYMTAB) {
+				edata = elf_getdata(scn, edata);
+				symbol_count = shdr.sh_size / shdr.sh_entsize;
+				for (i = 0; i < symbol_count; i++) {
+					gelf_getsym(edata, i, &sym);
+					tmp = elf_strptr(e, shdr.sh_link, sym.st_name);
+					if (!strcmp(symbol, tmp)) {
+						if (verbose > 0) {
+							printf("found symbol %s at %p\n",
+							       symbol, (void *)sym.st_value);
+						}
+						addr = (void *)sym.st_value;
+						len = (size_t)sym.st_size;
+						break;
+					}
+				}
+				if (!addr || !len)
+					errx(1, "symbol %s could not be located", symbol);
+				free(symbol);
+			}
+		}
+
+		elf_end(e);
+		close(fd);
+	}
 
 	if (verbose > 0)
-		printf("Base address: %p, length: %zu\n",
+		printf("base address: %p, length: %zu\n",
 		       addr, len);
 
 	pid = fork();
@@ -109,13 +172,13 @@ main(int argc, char *argv[])
 	}
 
 	if (verbose > 0)
-		printf("Mapping buffers into memory\n");
+		printf("mapping buffers into memory\n");
 
 	buf = map_buf(len);
 	buf_new = map_buf(len);
 
 	if (verbose > 0)
-		printf("Single stepping child with pid %jd\n",
+		printf("single stepping child with pid %jd\n",
 		       (intmax_t)pid);
 
 	wait(&stat);
@@ -152,11 +215,11 @@ main(int argc, char *argv[])
 		/* Build a memory region that tracks this buffer */
 		mr_old = build_mem_region(buf, len);
 		if (!mr_old)
-			errx(1, "Failed to build memory region\n");
+			errx(1, "failed to build memory region\n");
 		/* Build an rbtree that tracks this memory region */
 		mt_old = build_mem_tree(mr_old);
 		if (!mt_old)
-			errx(1, "Failed to build memory tree\n");
+			errx(1, "failed to build memory tree\n");
 
 		/* Single step the child in order to get the next
 		 * generation */
@@ -176,7 +239,7 @@ main(int argc, char *argv[])
 		/* Build a memory region that tracks this buffer */
 		mr_new = build_mem_region(buf_new, len);
 		if (!mr_new)
-			errx(1, "Failed to build memory region\n");
+			errx(1, "failed to build memory region\n");
 
 		/* Diff the original copy with the updated copy */
 		rdiff = diff_mem_region(mt_old, mr_new);