Change Details

Add another undefined instruction handler for compat32 and watch out for swp/swpb instructions. The atomic swap is done in assembly for simpler fault handling that we can detect; atomic_fcmpset_{8,32} could have been used, but it's harder to handle a fault as we have to do an atomic load of the old value for the compare-and-swap operation. atomic_swap_8 is easy to implement, but it suffers from the problem that there's no way to set a fault handler and communicate the error back properly swp_emulate_atomic just uses ll/sc to make for a simpler implementation. Sponsored by: Stormshield Sponsored by: Klara, Inc.

Add another undefined instruction handler for compat32 and watch out for swp/swpb instructions. The atomic swap is done in assembly for simpler fault handling that we can detect; atomic_fcmpset_{8,32} could have been used, but it's harder to handle a fault as we have to do an atomic load of the old value for the compare-and-swap operation. atomic_swap_8 is easy to implement, but it suffers from the problem that there's no way to set a fault handler and communicate the error back properly swp_emulate_atomic just uses ll/sc to make for a simpler implementation. SWP/SWPB were deprecated in ARMv6 and declared obsolete in ARMv7, but this implementation is motivated by some proprietary software that still uses SWP/SWPB. Because it's deprecated, emulation is pushed back behind a sysctl that defaults to OFF in GENERIC so that it doesn't potentially adversely affect package builds; it's unknown whether software may test for a functional swp/swpb instruction with the desire of using it later, so we err on the side of caution to ensure we don't end up with swp/swpb use in freebsd/arm packages (which are built on aarch64). The EMUL_SWP config option may be used to enable emulation by default in environments where emulation is desired and won't really be turned off. Sponsored by: Stormshield Sponsored by: Klara, Inc.

Add another undefined instruction handler for compat32 and watch out for swp/swpb instructions. The atomic swap is done in assembly for simpler fault handling that we can detect; atomic_fcmpset_{8,32} could have been used, but it's harder to handle a fault as we have to do an atomic load of the old value for the compare-and-swap operation. atomic_swap_8 is easy to implement, but it suffers from the problem that there's no way to set a fault handler and communicate the error back properly swp_emulate_atomic just uses ll/sc to make for a simpler implementation. SWP/SWPB were deprecated in ARMv6 and declared obsolete in ARMv7, but this implementation is motivated by some proprietary software that still uses SWP/SWPB. Because it's deprecated, emulation is pushed back behind a sysctl that defaults to OFF in GENERIC so that it doesn't potentially adversely affect package builds; it's unknown whether software may test for a functional swp/swpb instruction with the desire of using it later, so we err on the side of caution to ensure we don't end up with swp/swpb use in freebsd/arm packages (which are built on aarch64). The EMUL_SWP config option may be used to enable emulation by default in environments where emulation is desired and won't really be turned off. Sponsored by: Stormshield Sponsored by: Klara, Inc.