implement alternative way to get memusage using wait4

run now forks the benchmark command instead of simply calling exec.
Ressource usage of the benchmark is retrieved with a call to wait4.
But the reported value ru_maxrss differs from values in /proc/<pid>/status.

src/Makefile

@@ -15,7 +15,7 @@ MEMSIZE=$(shell echo $(MEMSIZE_KB)"* 1024" | bc)
 
 .PHONY: all clean
 
-all: $(OBJDIR)/print_status_on_exit.so $(OBJDIR)/allocators/bumpptr_alloc.so $(OBJDIR)/exec
+all: $(OBJDIR)/print_status_on_exit.so $(OBJDIR)/allocators/bumpptr_alloc.so $(OBJDIR)/run
 
 $(OBJDIR)/allocators/bumpptr_alloc.so: bumpptr_alloc.c Makefile | $(OBJDIR)/allocators
 	@echo "Compiling $@...";
@@ -26,7 +26,7 @@ $(OBJDIR)/print_status_on_exit.so: print_status_on_exit.c Makefile | $(OBJDIR)
 	@echo "Compiling $@...";
 	$(CC) $(LDFLAGS) -shared $(CFLAGS) -o $@ $<
 
-$(OBJDIR)/exec: exec.c Makefile | $(OBJDIR)
+$(OBJDIR)/run: run.c Makefile | $(OBJDIR)
 	@echo "Compiling $@...";
 	$(CC) $(LDFLAGS) $(CFLAGS) -o $@ $<
 

src/exec.c → src/run.c

@@ -2,35 +2,84 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <sys/resource.h>
+#include <sys/wait.h>
 #include <unistd.h>
 
+static int child(int argc, char* argv[])
+{
+	char **newargv = malloc(sizeof(char*) * argc);
+	if (newargv == NULL)
+	{
+		perror("malloc");
+		return 1;
+	}
+
+	for (int i = 0; i < argc; i++)
+	{
+		newargv[i] = argv[i];
+	}
+	newargv[argc] = NULL;
+
+	execvp(newargv[0], newargv);
+
+	perror("execvp");
+	return 1;
+}
+
 int main(int argc, char* argv[]) {
-	if (argc < 2) {
+	if (argc < 2)
+	{
 		printf("Usage: %s [-p LD_PRELOAD] [-l LD_LIBRARY_PATH] <cmd> [cmd args]\n", argv[0]);
 		printf("\tset LD_PRELOAD to ld_preload and call execvp <cmd> [cmd args]\n");
 		return 1;
 	}
 
+	int status, child_val;
+	struct rusage r_usage;
+
 	int i = 1;
-	for (; i < argc; i++) {
+	for (; i < argc; i++)
+	{
 		// Overwrite LD_PRELOAD.
-		if (strncmp(argv[i], "-p", 2) == 0) {
+		if (strncmp(argv[i], "-p", 2) == 0)
+		{
 			setenv("LD_PRELOAD", argv[i+1], 1);
 			i++;
 		// Overwrite LD_LIBRARY_PATH.
-		} else if (strncmp(argv[i], "-l", 2) == 0) {
+		} else if (strncmp(argv[i], "-l", 2) == 0)
+		{
 			setenv("LD_LIBRARY_PATH", argv[i+1], 1);
 			i++;
-		} else {
+		} else
+		{
 			break;
 		}
 	}
 
+	pid_t child_pid = fork();
 
-	// Run cmd.
-	execvp(argv[i], &argv[i]);
 
-	fprintf(stderr, "executing %s failed\n", argv[i]);
+	if (child_pid == 0)
+	{
+		return child(argc - i, &argv[i]);
+	}
+	else if (child_pid > 0)
+	{
+		/* Collect child */
+		wait4(child_pid, &status, 0, &r_usage);
+		printf("child memory usage = %ld\n", r_usage.ru_maxrss);
 
-	return 1;
+		 /* Get child status value */
+		 if (WIFEXITED(status))
+		 {
+		 	child_val = WEXITSTATUS(status);
+		 	exit(child_val);
+		 }
+	} else
+	{
+		perror("fork");
+	}
+
+	return 0;
 }