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
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