[alsa-devel] [PATCH] ASoC: prevent compilers from optimising pll calculation into __aeabi__uldivmod

[Stephen Warren]

Barry Song wrote at Wednesday, April 27, 2011 1:28 AM:
> The newest compiliers can optimize pll calculation in several codecs into
> __aeabi__uldivmod which doesn't exist in kernel.
> Then the link will fail:
> ERROR: "__aeabi_uldivmod" [sound/soc/codecs/snd-soc-wm8974.ko] undefined!
> ERROR: "__aeabi_uldivmod" [sound/soc/codecs/snd-soc-wm8940.ko] undefined!
> ERROR: "__aeabi_uldivmod" [sound/soc/codecs/snd-soc-wm8510.ko] undefined!
> This patch prevent the optimizaton by insert ASM.

Aren't there compiler flags that tell gcc it isn't operating in a hosted(?)
environment, and hence not to emit calls to these functions? If so, I
imagine they should be added to the kernel's core (or ARM arch ) makefiles.

I doubt __aeabi_uldivmod is the only function of this type. How was this
solved for other such functions; does the kernel implement the AEABI
functions, and this implementation is simply missing?

But yes either way, ask on the main kernel or ARM kernel mailing list
(ARM now CC'd)

diff --git a/sound/soc/codecs/wm8510.c b/sound/soc/codecs/wm8510.c
index db0dced..a636b15 100644
--- a/sound/soc/codecs/wm8510.c
+++ b/sound/soc/codecs/wm8510.c
@@ -258,6 +258,12 @@ static void pll_factors(unsigned int target, unsigned int source)
 	Nmod = target % source;
 	Kpart = FIXED_PLL_SIZE * (long long)Nmod;
 
+	/*
+	 * The following asm() prevents the compiler from optimising
+	 * into a standard EABI function __aeabi__uldivmod()
+	 */
+	asm("" : "+r"(source));
+
 	do_div(Kpart, source);
 
 	K = Kpart & 0xFFFFFFFF;

-- 
nvpublic