[Fault-injection-developer] [RFC] [PATCH] general symbol replacement

[Louis Z. <lou...@li...>]

Dear all,
	Following is a tiny tool used to change a symbol name in your module.
So you can replace, for example, 'kmalloc' with 'fmalloc'. And then you
can write fmalloc implementation yourself in a module. In this way, you
can intercept any software API in kernel only if it is not a macro. Any
comments?
-- 
Yours truly,
Louis Zhuang
---------------
Fault Injection Test Harness Project
BK tree: http://fault-injection.bkbits.net/linux-2.5
Home Page: http://sf.net/projects/fault-injection

# This is a BitKeeper generated patch for the following project:
# Project Name: Fault Injection Test Harness tools
# This patch format is intended for GNU patch command version 2.5 or higher.
# This patch includes the following deltas:
#	           ChangeSet	1.22    -> 1.25   
#	fith_utility/Makefile.am	1.1     -> 1.2    
#	fith_utility/configure.in	1.1     -> 1.2    
#	               (new)	        -> 1.2     fith_utility/replacesym/replacesym.c
#	               (new)	        -> 1.1     fith_utility/replacesym/Makefile.am
#
# The following is the BitKeeper ChangeSet Log
# --------------------------------------------
# 03/02/27	lo...@ha...	1.23
# Add replace symbol mechanism
# --------------------------------------------
# 03/02/27	lo...@ha...	1.24
# add replacesym
# --------------------------------------------
# 03/02/27	lo...@ha...	1.25
# Fix a bug -- Should seek in .strtab instead of .shstrtab
# --------------------------------------------
#
diff -Nru a/fith_utility/Makefile.am b/fith_utility/Makefile.am
--- a/fith_utility/Makefile.am	Tue Mar  4 09:06:35 2003
+++ b/fith_utility/Makefile.am	Tue Mar  4 09:06:35 2003
@@ -1,4 +1,4 @@
 AUTOMAKE_OPTIONS = foreign
 EXTRA_DIST = ./* 
 
-SUBDIRS = ficl 
+SUBDIRS = ficl replacesym 
diff -Nru a/fith_utility/configure.in b/fith_utility/configure.in
--- a/fith_utility/configure.in	Tue Mar  4 09:06:35 2003
+++ b/fith_utility/configure.in	Tue Mar  4 09:06:35 2003
@@ -36,4 +36,5 @@
 
 AC_OUTPUT([
 	Makefile 
-	ficl/Makefile])
+	ficl/Makefile
+	replacesym/Makefile])
diff -Nru a/fith_utility/replacesym/Makefile.am b/fith_utility/replacesym/Makefile.am
--- /dev/null	Wed Dec 31 16:00:00 1969
+++ b/fith_utility/replacesym/Makefile.am	Tue Mar  4 09:06:35 2003
@@ -0,0 +1,8 @@
+AUTOMAKE_OPTIONS = foreign
+sbin_PROGRAMS = replacesym
+
+include $(top_srcdir)/rules.mk
+
+replacesym_SOURCES = replacesym.c
+
+	
diff -Nru a/fith_utility/replacesym/replacesym.c b/fith_utility/replacesym/replacesym.c
--- /dev/null	Wed Dec 31 16:00:00 1969
+++ b/fith_utility/replacesym/replacesym.c	Tue Mar  4 09:06:35 2003
@@ -0,0 +1,98 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <sys/mman.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#include <errno.h>
+#include <asm/unistd.h>
+
+#include <elf.h>
+
+typedef Elf32_Ehdr Elf_Ehdr;
+typedef Elf32_Shdr Elf_Shdr;
+
+static int replace_symbol(void *map, int len, const char *old, const char *new)
+{
+	Elf_Ehdr *hdr;
+	Elf_Shdr *sechdrs;
+	char *strtab;
+	char *s;
+	int n;
+	
+	hdr = map;
+	if (len < sizeof(*hdr)) {
+		fprintf(stderr, "File is too short\n");
+		return -1;
+	}
+
+	/* Sanity checks against insmoding binaries or wrong arch,
+	 *            weird elf version */
+	if (memcmp(hdr->e_ident, ELFMAG, 4) != 0
+	    || hdr->e_type != ET_REL
+	    || hdr->e_shentsize != sizeof(*sechdrs)) {
+		fprintf(stderr, "File is weird\n");
+		return -1;
+	}					   	
+
+	sechdrs = map + hdr->e_shoff;
+	strtab  = map + sechdrs[hdr->e_shnum-1].sh_offset;
+	
+	n 	= sechdrs[hdr->e_shnum-1].sh_size;
+	s	= strtab;
+	while (n) {
+		int len;
+		
+		len = strnlen(s, n);
+		if (len >= n) {
+			fprintf(stderr, "Bad string table\n");
+			break;
+		}
+		printf("Symbol name:'%s'\n", s);
+		
+		if (!strcmp(s, old)) {
+			if (strlen(new) <= len) {
+				strncpy(s, new, len);
+			} else {
+				fprintf(stderr, 
+					"New symbol name is too long\n");
+			}
+		}
+		
+		s += len+1;
+		n -= len+1;
+	}	
+
+	return 0;
+}
+
+int main(int argc, char *argv[])
+{
+	int fd;
+	struct stat st;
+	void *map;
+	
+	if (argc != 4) {
+		printf("Usage: %s <module_file> <old_sym> <new_sym>\n", argv[0]);
+		exit(1);
+	}
+	
+	fd = open(argv[1], O_RDWR, 0);
+	if (fd < 0) {
+		perror("Unable to open file");
+		exit(1);
+	}
+
+	fstat(fd, &st);
+	map = mmap(NULL, st.st_size, PROT_WRITE|PROT_READ, MAP_SHARED, fd, 0);
+	if (MAP_FAILED == map) {
+		perror("Unable to mmap file");
+		exit(1);
+	}
+
+	replace_symbol(map, st.st_size, argv[2], argv[3]);
+	return 0;
+}