[sb2] Allow redirecting syscalls (not all are supported yet). JB#59837

preload/Makefile

@@ -11,6 +11,7 @@ objs := wrappers.o privatewrappers.o \
 	fdpathdb.o procfs.o mempcpy.o \
 	union_dirs.o \
 	system.o \
+	syscalls.o \
 	sb2context.o
 
 ifeq ($(shell uname -s),Linux)

preload/interface.master

@@ -111,6 +111,8 @@ GATE: int execve (const char *filename, char *const argv [], char *const envp[])
 GATE: int execvp (const char *file, char *const argv [])
 GATE: int execvpe(const char *file, char *const argv[], char *const envp[])
 
+GATE: long syscall(long number, ...) : pass_va_list
+
 GATE: int posix_spawn (pid_t *pid, const char *path, \
                        const posix_spawn_file_actions_t *file_actions, \
                        const posix_spawnattr_t *attrp, \

preload/syscalls.c

@@ -0,0 +1,60 @@
+/*
+ *
+ * SPDX-FileCopyrightText: 2023, Jolla Ltd.
+ * SPDX-License-Identifier: LGPL-2.1
+ *
+ * syscallgate -- syscall() GATE for the scratchbox2 preload library
+ *
+ * Copyright (C) 2023 Jolla Ltd.
+ */
+
+#include <asm-generic/unistd.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+
+#include "libsb2.h"
+#include "exported.h"
+
+#define FORWARD_TO_WRAPPER(sysc, ...) \
+        case SYS_ ## sysc: { \
+            ret = sysc(__VA_ARGS__); \
+        } break
+
+extern long syscall_gate(int *result_errno_ptr,
+    long (*real_syscall_ptr)(long number, ...),
+    const char *realfnname, long number, va_list args)
+{
+    long arg0 = va_arg(args, long);
+    long arg1 = va_arg(args, long);
+    long arg2 = va_arg(args, long);
+    long arg3 = va_arg(args, long);
+    long arg4 = va_arg(args, long);
+    long arg5 = va_arg(args, long);
+
+    long ret;
+    switch (number) {
+        FORWARD_TO_WRAPPER(execve, arg0, arg1, arg2);
+        FORWARD_TO_WRAPPER(openat, arg0, arg1, arg2, arg3);
+        // FORWARD_TO_WRAPPER(open_by_handle_at, ...)
+        FORWARD_TO_WRAPPER(open, arg0, arg1, arg2);
+        FORWARD_TO_WRAPPER(connect, arg0, arg1, arg2);
+        FORWARD_TO_WRAPPER(sendto, arg0, arg1, arg2, arg3, arg4, arg5);
+        FORWARD_TO_WRAPPER(sendmsg, arg0, arg1, arg2);
+        FORWARD_TO_WRAPPER(recvfrom, arg0, arg1, arg2, arg3, (struct sockaddr *)arg4, arg5);
+        FORWARD_TO_WRAPPER(recvmsg, arg0, arg1, arg2);
+        FORWARD_TO_WRAPPER(accept, arg0, arg1, arg2);
+        FORWARD_TO_WRAPPER(accept4, arg0, arg1, arg2, arg3);
+        FORWARD_TO_WRAPPER(utimensat, arg0, arg1, arg2, arg3);
+        FORWARD_TO_WRAPPER(utime, arg0, arg1);
+        FORWARD_TO_WRAPPER(utimes, arg0, arg1);
+        FORWARD_TO_WRAPPER(fcntl, arg0, arg1, arg2);
+        FORWARD_TO_WRAPPER(futimesat, arg0, arg1, arg2);
+        default: {
+            ret = real_syscall_ptr(number, arg0, arg1, arg2, arg3, arg4, arg5);
+            break;
+        }
+    };
+    if (result_errno_ptr) *result_errno_ptr = errno;
+    return ret;
+}
+