2 messages, 2 authors, 2021-09-27 · open the first message on its own page
From: Florian Weimer <hidden>
Date: 2021-09-27 18:51:36
* Richard Palethorpe:
+#define __SC_COMPAT_CAST(t, a) \ + (__typeof(__builtin_choose_expr(__TYPE_IS_L(t), 0, 0U))) \ + (unsigned int)a
So this casts to int (triggering sign extension) if the type on the 64-bit kernel side is long? But not in other cases (unsigned long, pointer)? Just double-checking. Thanks, Florian
From: Arnd Bergmann <arnd@arndb.de>
Date: 2021-09-27 19:02:21
On Mon, Sep 27, 2021 at 8:51 PM Florian Weimer [off-list ref] wrote:
* Richard Palethorpe:quoted
+#define __SC_COMPAT_CAST(t, a) \ + (__typeof(__builtin_choose_expr(__TYPE_IS_L(t), 0, 0U))) \ + (unsigned int)aSo this casts to int (triggering sign extension) if the type on the 64-bit kernel side is long? But not in other cases (unsigned long, pointer)? Just double-checking.
Correct, this is the only case that is not already handled: anything smaller
than a 'long' is the same size on all architectures we support and we
ensure those are correctly sign- or zero-extended. 'unsigned long'
and any pointer are zero-extended by the entry code from 32-bit user
space to a 64-bit register in the kernel. Only signed 'long' requires
explicit sign-extending from the userspace 'long' to the kernel function
argument.
Arnd