Am 16.07.2021 um 11:10 schrieb Michael Schmitz:
Eric, On 16/07/21 1:29 am, Eric W. Biederman wrote:I have been digging into this some more and I have found one place that I am having a challenge dealing with. In arch/m68k/fpsp040/skeleton.S there is an assembly version of copy_from_user that calls fpsp040_die when the bytes can not be read. Now fpsp040_die is just: /* * This function is called if an error occur while accessing * user-space from the fpsp040 code. */ asmlinkage void fpsp040_die(void) { do_exit(SIGSEGV); } The problem here is the instruction emulation performed in the fpsp040 code performs a very minimal saving of registers. I don't think even the normal system call entry point registers that are saved are present at that point. Is there any chance you can help me figure out how to get a stack frame with all of the registers present before fpsp040_die is called?I suppose adding the following code (untested) to entry.S: ENTRY(fpsp040_die) SAVE_ALL_INT jbsr fpsp040_die_c jra ret_from_exception along with renaming above C entry point to fpsp040_die_c would add the basic saved registers, but these would not necessarily reflect the state of the processor when the fpsp040 trap was called. Is that what you're after?
I should have looked more closely at skeleton.S - most FPU exceptions handled there call trap_c the same way as is done for generic traps, i.e. SAVE_ALL_INT before, ret_from_exception after.
Instead of adding code to entry.S, much better to add it in skeleton.S. I'll try to come up with a way to test this code path (calling fpsp040_die from the dz exception hander seems much the easiest way) to make sure this doesn't have side effects.
Does do_exit() ever return? Cheers, Michael
