Fix heap buffer overflow for `string_match` benchmark when `NO_MMAP` flag is used.

[dimstav23]

What is this PR doing:

Fixes #9 This PR adapts the buffer allocation for the string_match benchmark when the NO_MMAP flag is set to eliminate the heap buffer overflow detected by ASan.

How to test this PR:

Compile the benchmarks with a patch that enables the NO_MMAP flag and AddressSanitizer (ASan):

$ git clone https://github.com/kozyraki/phoenix.git

$ git fetch origin pull/10/head:sm_overflow_fix

$ git switch sm_overflow_fix

$ cd phoenix/phoenix-2.0/

$ echo 'diff --git a/phoenix-2.0/tests/string_match/Makefile b/phoenix-2.0/tests/string_match/Makefile
index be7d94b..310b965 100644
--- a/phoenix-2.0/tests/string_match/Makefile
+++ b/phoenix-2.0/tests/string_match/Makefile
@@ -46,16 +46,16 @@ default: all
 all: $(PROGS)
 
 string_match: $(STR_MATCH_OBJS) $(LIB_DEP)
-    $(CC) $(CFLAGS) -o $@ $(STR_MATCH_OBJS) $(LIBS)
+    $(CC) $(CFLAGS) -o $@ $(STR_MATCH_OBJS) $(LIBS) -fsanitize=address
 
 string_match-seq: $(STR_MATCH_SEQ_OBJS)
-    $(CC) $(CFLAGS) -o $@ $(STR_MATCH_SEQ_OBJS) $(LIBS)
+    $(CC) $(CFLAGS) -o $@ $(STR_MATCH_SEQ_OBJS) $(LIBS) -fsanitize=address
 
 string_match-pthread: $(STR_MATCH_PTHREAD_OBJS)
-    $(CC) $(CFLAGS) -o $@ $(STR_MATCH_PTHREAD_OBJS) $(LIBS)
+    $(CC) $(CFLAGS) -o $@ $(STR_MATCH_PTHREAD_OBJS) $(LIBS) -fsanitize=address
 
 %.o: %.c
-    $(CC) $(CFLAGS) -c $< -o $@ -I$(HOME)/$(INC_DIR)
+    $(CC) $(CFLAGS) -c $< -o $@ -I$(HOME)/$(INC_DIR) -DNO_MMAP=1 -fsanitize=address
 
 clean:
     rm -f $(PROGS) $(STR_MATCH_OBJS) $(STR_MATCH_SEQ_OBJS) $(STR_MATCH_PTHREAD_OBJS)' > sm_overflow.patch

$ git apply sm_overflow.patch

$ make

Retrieve the inputs for the string_match benchmark:

$ cd tests/string_match

$ wget http://csl.stanford.edu/~christos/data/string_match.tar.gz

$ tar -xvf string_match.tar.gz

Run the string_matchbenchmark and observe the output of ASan:

$ ./string_match string_match_datafiles/key_file_50MB.txt

With the change included in this PR, ASan does not report any heap buffer overflow error.

Tested on:

OS: Ubuntu 22.04.4 LTS Kernel: 6.2.0-39-generic gcc: 11.4.0