updated some comments in the patch code

Author: elfmaster

Makefile

@@ -1,7 +1,7 @@
 BUILD_DIR = './build'
 INTERP_PATH = $(PWD)/build/shiva
 PATCH_PATH = "modules/aarch64_patches"
-GCC_OPTS= -fPIC -ggdb -c
+GCC_OPTS= -fPIC -ggdb -c -DDEBUG
 OBJ_LIST=shiva.o shiva_util.o shiva_signal.o shiva_ulexec.o shiva_auxv.o	\
     shiva_module.o shiva_trace.o shiva_trace_thread.o shiva_error.o shiva_maps.o shiva_analyze.o \
     shiva_callsite.o shiva_target.o shiva_xref.o shiva_transform.o shiva_so.o shiva_post_linker.o

modules/aarch64_patches/dataonly_interposing/test_data.c

@@ -11,6 +11,7 @@ int foo(void)
 
 int bar(void)
 {
+	static int data_var2 = 10;
 	printf("I am a function that won't be patched\n");
 	printf("I'm accessing data_var and its value is %#x\n", data_var);
 	return 0;

modules/aarch64_patches/fsplice/example2/fsplice_host.patched

@@ -2,21 +2,20 @@
 #include <stdio.h>
 #include "shiva_module.h"
 
+/*
+ * Splice C code into function foo()
+ * At Offset 0x72c - 0x73c
+ */
 
 SHIVA_T_SPLICE_FUNCTION(foo, 0x72c, 0x73c)
 {
-	/*
-	 * Attach x0 (arg1) to a use-able variable. (Which
-	 * will live in the .bss).
-	 */
-	SHIVA_T_PAIR_X0(str);
+	SHIVA_T_PAIR_X0(str); // register char *str asm("x0");
 	if (str != NULL) {
-		fprintf(stdout, "(fprintf version): Printing arg: %s\n", str);
+		fprintf(stdout, "Printing str: %s\n", str);
 	}
-	bar();
 }
 
-int bar(void)
-{
-	printf("I am the new bar\n");
-}
+
+
+
+

modules/aarch64_patches/fsplice/example2/fsplice_patch.c

@@ -1,3 +1,7 @@
+/*
+ * The original program that we want to patch
+ */
+
 #include <stdio.h>
 
 const char *banner = "ElfMaster";
@@ -8,7 +12,7 @@ int foo(int num, char *str)
 	if (num == 7)
 		goto done;
 	strcpy(global_buf, banner);
-	printf("Printing str: %s\n", str); // <- replace with patch
+	printf("Printing str: %s\n", str); // <- splice code in here
 done:
 	return 0;
 }

modules/aarch64_patches/fsplice/example2/fsplice_patch.o

@@ -1,20 +1,36 @@
+/*
+ * Patch code.
+ * Patch 1. Create a new .data variable, data_val
+ * Patch 2. Splice code into function foo() (Very intensive operation)
+ * Patch 3. Rewrite function bar() via symbol interposition
+ */
+
 #include <stdint.h>
 #include <stdio.h>
 #include "shiva_module.h"
 
-int data_val = 7;
-extern char global_buf[255];
+int data_val = 7; // adds in a new .data global variable
+extern char global_buf[255]; // links to external global_buf[] variable
 
+/*
+ * The SHIVA_T_SPLICE_FUNCTION will splice it's body of C code
+ * into the function foo() at address 0x818. It won't fit between
+ * 0x818 and 0x828 so it extends the size of the function.
+ */
 SHIVA_T_SPLICE_FUNCTION(foo, 0x818, 0x828)
 {
-	SHIVA_T_PAIR_BP_16(str);
+	SHIVA_T_PAIR_BP_16(str); //equiv to char *str = [bp, #16]
 	if (str != NULL) {
 		fprintf(stdout, "Printing str: %s\n", str);
 	}
 	fprintf(stdout, "global_buf: %s\n", global_buf);
 	bar();
 }
 
+/*
+ * Completely re-writes the function bar() so that it
+ * prints data_val + 1
+ */
 int bar(void)
 {
 	data_val = data_val + 1;

modules/aarch64_patches/fsplice/example6/fsplice_host.c

@@ -1,9 +1,9 @@
 INTERP_PATH="/lib/shiva"
 SHIVA-LD_PATH="../../../tools/shiva-ld/shiva-ld"
-all:
+patch:
 	# Build the module ro_patch.c with a large code model
 	gcc -mcmodel=large -fno-pic -I ../ -fno-stack-protector -c ro_patch.c
-
+prog:
 	# Build the program we are patching
 	gcc -O0 test_rodata.c -o test_rodata