Messages in this thread | | | From | Nick Desaulniers <> | Date | Mon, 1 Jun 2020 15:19:23 -0700 | Subject | Re: arm64/acpi: NULL dereference reports from UBSAN at boot |
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On Mon, Jun 1, 2020 at 2:57 PM Ard Biesheuvel <ardb@kernel.org> wrote: > > On Mon, 1 Jun 2020 at 23:52, Nick Desaulniers <ndesaulniers@google.com> wrote: > > > > 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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