flushpl

commit 2ee44627eff9037e50c4c508a1fcc83322850345
Author: Louis Burda <quent.burda@gmail.com>
Date:   Mon, 19 Sep 2022 18:04:49 +0200

Working preload

Diffstat:
A
.gitignore
 | 
2
++
A
Makefile
 | 
5
+++++
A
flush.c
 | 
23
+++++++++++++++++++++++
A
test.c
 | 
7
+++++++

4 files changed, 37 insertions(+), 0 deletions(-)
diff --git a/.gitignore b/.gitignore
@@ -0,0 +1,2 @@
+flush.so
+test
diff --git a/Makefile b/Makefile
@@ -0,0 +1,5 @@
+CFLAGS = -nostartfiles -fPIC -shared --std=gnu99
+LDLIBS = -ldl
+
+flush.so: flush.c
+	$(CC) -o $@ $< $(CFLAGS) $(LDLIBS)
diff --git a/flush.c b/flush.c
@@ -0,0 +1,23 @@
+#include <dlfcn.h>
+
+#include <stdlib.h>
+#include <stdio.h>
+
+size_t
+fwrite(const void *src, size_t size, size_t count, FILE *file)
+{
+	static size_t (*func)(const void *, size_t, size_t, FILE *) = NULL;
+	static void *libc = NULL;
+	size_t ret;
+
+	if (!libc) libc = dlopen("libc.so.6", RTLD_GLOBAL | RTLD_LAZY);
+	if (!func) func = dlsym(libc, "fwrite");
+
+	if (!libc || !func) exit(1);
+
+	ret = (*func)(src, size, count, file);
+	fflush(file);
+
+	return ret;
+}
+
diff --git a/test.c b/test.c
@@ -0,0 +1,7 @@
+#include <stdio.h>
+
+int
+main()
+{
+	fwrite("Hello\n", 6, 1, stdout);
+}