Robert Millan wrote: > On Tue, Sep 23, 2008 at 04:11:34PM +0200, Mathias Krause wrote: >>> I see. But why not just add "ecx" to clobber list instead? Then a dummy >>> variable isn't needed. >> When doing so the compiler is unable to find another register called >> %ecx to assign the value of f as input value. He cannot use %ecx because >> by mentioning it in the clobber list you already told him that register >> may change it's value at any time within the asm statement. That for the >> "kudge" with the dummy output variable is needed but it should get >> optimized away since it's value is never used. It's only usage is to >> tell the compiler that the value of %ecx has changed. > > Ok. > >>>> The memory clobber is needed since you cannot know what the called >>>> function will actually do with the memory and to ensure all cached >>>> values are actually written back to memory before calling f(). >>> Is this really a problem? If the payload expects to return, it isn't >>> supposed to modify coreboot's memory at all. If it does, I'd say it's >>> normal that things break. >> Not the return of f() is the problem but missing memory writes _before_ >> calling it. If coreboot does some memory modifications that are relevant >> for f() they should be taken out of registers and written back to memory >> before calling f(). Otherwise f() may break. > > Makes sense. Thanks for the explanation.
You're welcome. > Here's a new patch incorporating your suggestions. Thanks. Mathias -- coreboot mailing list: [email protected] http://www.coreboot.org/mailman/listinfo/coreboot
