On 18.05.2020 16:18, Russell King - ARM Linux admin wrote: > On Mon, May 18, 2020 at 03:12:06PM +0200, Fredrik Strupe wrote: >> call_undef_hook() in traps.c applies the same instr_mask for both 16-bit >> and 32-bit thumb instructions. If instr_mask then is only 16 bits wide >> (0xffff as opposed to 0xffffffff), the first half-word of 32-bit thumb >> instructions will be masked out. This makes the function match 32-bit >> thumb instructions where the second half-word is equal to instr_val, >> regardless of the first half-word. >> >> The result in this case is that all undefined 32-bit thumb instructions >> with the second half-word equal to de01 (udf #1) work as breakpoints >> and will raise a SIGTRAP instead of a SIGILL, instead of just the one >> intended 16-bit instruction. An example of such an instruction is >> eaa0b650, which is unallocated according to Arm ARM and should raise a >> SIGILL, but instead raises a SIGTRAP. > > How can 0xeaa0b650 match 0xde01 when masked with 0xffff ? >
Sorry, that is a typo; it should say 0xeaa0de01. For reference, this is similar to the problem with SETEND emulation that was fixed in commit fc2266011acc in the mainline kernel (or as discussed here: https://lkml.org/lkml/2020/4/8/274). Fredrik
