On Mon, 2015-09-07 at 09:08 +0200, Christophe LEROY wrote: > Hi Michael > > Le 07/09/2015 03:14, Michael Ellerman a écrit : > > On Sun, 2015-09-06 at 23:01 +0200, Michal Sojka wrote: > >> I found the problem. The compiler replaces an assignment with a call to > >> memcpy. The following patch fixes the problem for me. However, I'm not > >> sure whether this is the real solution. I guess the compiler is free to > >> generate a call to memcpy wherever it wants so other compilers or other > >> optimization levels may need fixes at other places. What do others > >> think? > > I think you're right that it's not a good solution, the compiler could > > generate > > other calls to memcpy depending on various factors, and people will add new > > code that causes memcpy to get called and it will break your platform. > > > > Christophe, am I right that the problem here is that your new memcpy() > > doesn't > > work until later in boot when caches are enabled? > > That's right, memset() and memcpy() are for setting/copying data into > cacheable RAM. > They are using dczb instruction in order to avoid wasting time loading > the cacheline with data that will be overwritten. > > memset_io() and memcpy_toio() are the functions to use when using not > cacheable memory. > > The issue identified by Michal is in function setup_cpu_spec() which is > called by identify_cpu(). identify_cpu() is called from early_init(). > In the begining of early_init(), there is (code from Paul in 2005) > > /* First zero the BSS -- use memset_io, some platforms don't have > * caches on yet */ > memset_io((void __iomem *)PTRRELOC(&__bss_start), 0, > __bss_stop - __bss_start); > > It shows that it is already expected that the cache is not active yet > and standard memset() shall not be used yet. That's the same with memcpy().
Thanks for the explanation. > I think GCC uses memcpy() in well known situations like initialising > structures or copying structures. > Shouldn't we just avoid this kind of actions in the very few early init > functions ? Which are the "very few" early init functions? Can you make a list, for 32-bit and 64-bit? And can we keep it updated over time and not introduce regressions? cheers _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
