From 648a139af36d6803fbe0674d4c6d461f46564e84 Mon Sep 17 00:00:00 2001
From: Daniel Bertalan <dani@danielbertalan.dev>
Date: Sat, 13 Nov 2021 09:28:56 +0100
Subject: [PATCH] Kernel+LibC: Pass off_t to pread() via a pointer

`off_t` is a 64-bit signed integer, so passing it in a register on i686
is not the best idea.

This fix gets us one step closer to making the LLVM port work.
---
 Kernel/Process.h                   | 2 +-
 Kernel/Syscalls/read.cpp           | 4 +++-
 Userland/Libraries/LibC/unistd.cpp | 2 +-
 3 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/Kernel/Process.h b/Kernel/Process.h
index f212074fc2..64feb852a0 100644
--- a/Kernel/Process.h
+++ b/Kernel/Process.h
@@ -294,7 +294,7 @@ public:
     ErrorOr<FlatPtr> sys$open(Userspace<const Syscall::SC_open_params*>);
     ErrorOr<FlatPtr> sys$close(int fd);
     ErrorOr<FlatPtr> sys$read(int fd, Userspace<u8*>, size_t);
-    ErrorOr<FlatPtr> sys$pread(int fd, Userspace<u8*>, size_t, off_t);
+    ErrorOr<FlatPtr> sys$pread(int fd, Userspace<u8*>, size_t, Userspace<off_t*>);
     ErrorOr<FlatPtr> sys$readv(int fd, Userspace<const struct iovec*> iov, int iov_count);
     ErrorOr<FlatPtr> sys$write(int fd, Userspace<const u8*>, size_t);
     ErrorOr<FlatPtr> sys$writev(int fd, Userspace<const struct iovec*> iov, int iov_count);
diff --git a/Kernel/Syscalls/read.cpp b/Kernel/Syscalls/read.cpp
index 4dc7b0d15a..a001285925 100644
--- a/Kernel/Syscalls/read.cpp
+++ b/Kernel/Syscalls/read.cpp
@@ -90,7 +90,7 @@ ErrorOr<FlatPtr> Process::sys$read(int fd, Userspace<u8*> buffer, size_t size)
     return TRY(description->read(user_buffer.value(), size));
 }
 
-ErrorOr<FlatPtr> Process::sys$pread(int fd, Userspace<u8*> buffer, size_t size, off_t offset)
+ErrorOr<FlatPtr> Process::sys$pread(int fd, Userspace<u8*> buffer, size_t size, Userspace<off_t*> userspace_offset)
 {
     VERIFY_PROCESS_BIG_LOCK_ACQUIRED(this)
     REQUIRE_PROMISE(stdio);
@@ -98,6 +98,8 @@ ErrorOr<FlatPtr> Process::sys$pread(int fd, Userspace<u8*> buffer, size_t size,
         return 0;
     if (size > NumericLimits<ssize_t>::max())
         return EINVAL;
+    off_t offset;
+    TRY(copy_from_user(&offset, userspace_offset));
     if (offset < 0)
         return EINVAL;
     dbgln_if(IO_DEBUG, "sys$pread({}, {}, {}, {})", fd, buffer.ptr(), size, offset);
diff --git a/Userland/Libraries/LibC/unistd.cpp b/Userland/Libraries/LibC/unistd.cpp
index 88d28f759d..c08c377998 100644
--- a/Userland/Libraries/LibC/unistd.cpp
+++ b/Userland/Libraries/LibC/unistd.cpp
@@ -296,7 +296,7 @@ ssize_t read(int fd, void* buf, size_t count)
 
 ssize_t pread(int fd, void* buf, size_t count, off_t offset)
 {
-    int rc = syscall(SC_pread, fd, buf, count, offset);
+    int rc = syscall(SC_pread, fd, buf, count, &offset);
     __RETURN_WITH_ERRNO(rc, rc, -1);
 }