linux-user/arm: Fix identification of syscall numbers

Our code to identify syscall numbers has some issues:
 * for Thumb mode, we never need the immediate value from the insn,
   but we always read it anyway
 * bad immediate values in the svc insn should cause a SIGILL, but we
   were abort()ing instead (via "goto error")

We can fix both these things by refactoring the code that identifies
the syscall number to more closely follow the kernel COMPAT_OABI code:
 * for Thumb it is always r7
 * for Arm, if the immediate value is 0, then this is an EABI call
   with the syscall number in r7
 * otherwise, we XOR the immediate value with 0x900000
   (ARM_SYSCALL_BASE for QEMU; __NR_OABI_SYSCALL_BASE in the kernel),
   which converts valid syscall immediates into the desired value,
   and puts all invalid immediates in the range 0x100000 or above
 * then we can just let the existing "value too large, deliver
   SIGILL" case handle invalid numbers, and drop the 'goto error'

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Message-id: 20200420212206.12776-5-peter.maydell@linaro.org

0 files changed, 0 insertions, 0 deletions