Hook realpath(3) for /proc/self/exe

Makefile

@@ -1,7 +1,7 @@
 CC ?= clang
 TERMUX_BASE_DIR ?= /data/data/com.termux/files
 CFLAGS += -Wall -Wextra -Werror -Wshadow -fvisibility=hidden -std=c17
-C_SOURCE := src/termux-exec.c src/exec-variants.c src/termux-readlink.c
+C_SOURCE := src/termux-exec.c src/exec-variants.c src/termux-readlink.c src/termux-realpath.c
 CLANG_FORMAT := clang-format --sort-includes --style="{ColumnLimit: 120}" $(C_SOURCE) tests/fexecve.c tests/system-uname.c tests/print-argv0.c tests/popen.c
 CLANG_TIDY ?= clang-tidy
 

src/termux-realpath.c

@@ -0,0 +1,21 @@
+#define _GNU_SOURCE
+#include <dlfcn.h>
+#include <fcntl.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+
+__attribute__((visibility("default"))) char* _Nullable realpath(const char* _Nonnull path, char* _Nullable resolved) {
+      char* (*orig_realpath)(const char*, char*);
+      orig_realpath = dlsym(RTLD_NEXT, "realpath");
+
+  if (strcmp(path, "/proc/self/exe") == 0) {
+    const char *termux_self_exe = getenv("TERMUX_EXEC__PROC_SELF_EXE");
+    if (termux_self_exe) {
+		   path = termux_self_exe;
+    }
+  }
+
+  return orig_realpath(path, resolved);
+}