On Mon, Jun 1, 2020 at 2:57 PM Ard Biesheuvel [off-list ref] wrote:
On Mon, 1 Jun 2020 at 23:52, Nick Desaulniers [off-list ref] wrote:
quoted
Anyways, it looks like the address of member from NULL subexpression
looks problematic. I wonder if offsetof can be used here?
#define ACPI_OFFSET(d, f) ACPI_PTR_DIFF (offsetof(d, f), (void *) 0)
Seems to work in my basic test case. Untested in the kernel.
IIUC, ACPI_OFFSET is trying to calculate the difference between the
offset of a member of a struct and 0? Isn't that the tautology `x - 0
== x`?
No. ACPI_OFFSET() is just a poor person's version of offsetof().
(Note that it calculates the difference between &(((d *) 0)->f) and
(void *)0x0, so the 0x0 term is there on both sides)
Got it. So we're trying to avoid including stddef.h? Can
__builtin_offsetof be used here?
#define ACPI_OFFSET(d, f) ACPI_PTR_DIFF (__builtin_offsetof(d, f), (void *) 0)
The oldest version of GCC in godbolt.org (4.1) supports this builtin.
--
Thanks,
~Nick Desaulniers
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