On 22/01/2025 10:26, Arnd Bergmann wrote:
On Wed, Jan 22, 2025, at 11:07, Niklas Cassel wrote:
On Tue, Jan 21, 2025 at 05:46:43PM +0000, Jon Hunter wrote:
diff --git a/drivers/misc/pci_endpoint_test.c b/drivers/misc/>>
This change breaks building the kernel with GCC v7 and I see ...
ERROR: modpost: "__aeabi_uldivmod" [drivers/misc/pci_endpoint_test.ko]
undefined!
ERROR: modpost: "__aeabi_ldivmod" [drivers/misc/pci_endpoint_test.ko]
undefined!
I know that this is an old GCC version, but this is a farm builder and the
kernel still indicates that GCC v5.1 is still supported [0].
do you have any idea what is going on here?
I'm a bit puzzled, since looking at other reports of this error,
e.g.:
https://lore.kernel.org/all/20241018151016.3496613-1-arnd@xxxxxxxxxx/
using div_u64() is usually the solution for this problem (for things that
are not performance critical), not the cause of it... any ideas?
I have tried to look at the email thread, but not tried to reproduce
it yet. I have two ideas about what might be happening:
a) something causes a /different/ division to call into
__aeabi_uldivmod(), not the one from div_u64().
b) the compiler notices one of the arguments to div_u64() being
constant in some cases and splits the calling function into
two special cases, for both the constant and non-constant
cases. This sometimes confuses the __builtin_constant_p()
in do_div() that decides to fall back to a 32-bit division.
Try looking at the .s file when you run
'make drivers/misc/pci_endpoint_test.s' to see where exactly it
calls the two division functions, maybe you see the problem then,
otherwise I can try to reproduce it here.
FWIW I have encountered similar problems with this before with this
compiler ...
https://lore.kernel.org/linux-tegra/7733a4ca-330b-4127-af12-33f376fbbc47@xxxxxxxxxx/
Jon
--
nvpublic
