@@ -884,6 +884,33 @@ static inline int host_to_target_sock_type(int host_type)
return target_type;
}
+/*
+ * If the guest is using a 32 bit ABI then we should try to ask the kernel
+ * to provide 32-bit offsets in getdents syscalls, as otherwise some
+ * filesystems will return 64-bit hash values which we can't fit into
+ * the field sizes the guest ABI mandates.
+ */
+#ifndef FD_32BIT_MODE
+#define FD_32BIT_MODE 2
+#endif
+
+static inline void request_32bit_fs(int fd)
+{
+#if HOST_LONG_BITS > TARGET_ABI_BITS
+ /*
+ * Ignore errors, which are likely due to the host kernel being
+ * too old to support FD_32BIT_MODE. We'll continue anyway, which
+ * might or might not work, depending on the guest code and on the
+ * host filesystem.
+ */
+ int flags = fcntl(fd, F_GETFD);
+ if (flags == -1) {
+ return;
+ }
+ fcntl(fd, F_SETFD, flags | FD_32BIT_MODE);
+#endif
+}
+
static abi_ulong target_brk;
static abi_ulong target_original_brk;
static abi_ulong brk_page;
@@ -7725,6 +7752,7 @@ static abi_long do_syscall1(void *cpu_env, int num, abi_long arg1,
target_to_host_bitmask(arg2, fcntl_flags_tbl),
arg3));
fd_trans_unregister(ret);
+ request_32bit_fs(ret);
unlock_user(p, arg1, 0);
return ret;
#endif
@@ -7735,6 +7763,7 @@ static abi_long do_syscall1(void *cpu_env, int num, abi_long arg1,
target_to_host_bitmask(arg3, fcntl_flags_tbl),
arg4));
fd_trans_unregister(ret);
+ request_32bit_fs(ret);
unlock_user(p, arg2, 0);
return ret;
#if defined(TARGET_NR_name_to_handle_at) && defined(CONFIG_OPEN_BY_HANDLE)
@@ -7746,6 +7775,7 @@ static abi_long do_syscall1(void *cpu_env, int num, abi_long arg1,
case TARGET_NR_open_by_handle_at:
ret = do_open_by_handle_at(arg1, arg2, arg3);
fd_trans_unregister(ret);
+ request_32bit_fs(ret);
return ret;
#endif
case TARGET_NR_close:
@@ -7790,6 +7820,7 @@ static abi_long do_syscall1(void *cpu_env, int num, abi_long arg1,
return -TARGET_EFAULT;
ret = get_errno(creat(p, arg2));
fd_trans_unregister(ret);
+ request_32bit_fs(ret);
unlock_user(p, arg1, 0);
return ret;
#endif
@@ -12419,6 +12450,7 @@ static abi_long do_syscall1(void *cpu_env, int num, abi_long arg1,
}
ret = get_errno(memfd_create(p, arg2));
fd_trans_unregister(ret);
+ request_32bit_fs(ret);
unlock_user(p, arg1, 0);
return ret;
#endif
If the guest is 32 bit then there is a potential problem if the host gives us back a 64-bit sized value that we can't fit into the ABI the guest requires. This is a theoretical issue for many syscalls, but a real issue for directory reads where the host is using ext3 or ext4. There the 'offset' values retured via the getdents syscall are hashes, and on a 64-bit system they will always fill the full 64 bits. Use the FD_32BIT_MODE fd flag to tell the kernel to stick to 32-bit sized hashes for fds used by the guest. This is an RFC patch because the kernel patch that adds the new fd flag hasn't yet been accepted upstream. The kernel patch is: https://patchew.org/QEMU/20200529072017.2906-1-linus.walleij@linaro.org/ Signed-off-by: Peter Maydell <peter.maydell@linaro.org> --- This is just a minor update of the testing patch I sent out in the thread discussing Linus's v1 kernel patch. linux-user/syscall.c | 32 ++++++++++++++++++++++++++++++++ 1 file changed, 32 insertions(+) -- 2.20.1