Re: [PATCH net-next] stmmac: fix signed 64-bit division

[David Miller]

From: Arnd Bergmann <arnd@xxxxxxxx>
Date: Fri,  6 Jul 2018 15:36:07 +0200

> I link error on 32-bit ARM points to yet another arithmetic bug:
> 
> drivers/net/ethernet/stmicro/stmmac/stmmac_tc.o: In function `tc_setup_cbs':
> stmmac_tc.c:(.text+0x148): undefined reference to `__aeabi_uldivmod'
> stmmac_tc.c:(.text+0x1fc): undefined reference to `__aeabi_uldivmod'
> stmmac_tc.c:(.text+0x308): undefined reference to `__aeabi_uldivmod'
> stmmac_tc.c:(.text+0x320): undefined reference to `__aeabi_uldivmod'
> stmmac_tc.c:(.text+0x33c): undefined reference to `__aeabi_uldivmod'
> drivers/net/ethernet/stmicro/stmmac/stmmac_tc.o:stmmac_tc.c:(.text+0x3a4): more undefined references to `__aeabi_uldivmod' follow
> 
> I observe that the last change to add the 'ul' prefix was incorrect,
> as it did not turn the result of the multiplication into a 64-bit
> expression on 32-bit architectures. Further, it seems that the
> do_div() macro gets confused by the fact that we pass a signed
> variable rather than unsigned into it.
> 
> This changes the code to instead use the div_s64() helper that is
> meant for signed division, along with changing the constant suffix
> to 'll' to actually make it a 64-bit argument everywhere, fixing
> both of the issues I pointed out.
> 
> I'm not completely convinced that this makes the code correct, but
> I'm fairly sure that we have two problems less than before.
> 
> Fixes: 1f705bc61aee ("net: stmmac: Add support for CBS QDISC")
> Fixes: c18a9c096683 ("net: stmmac_tc: use 64-bit arithmetic instead of 32-bit")
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>

Applied, thank you.