Or more generally, what happens if an swi instruction with an opcode !=0 is executed on such a kernel? Does it produce a signal? I ask because I’d like to trap it.
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Or more generally, what happens if an swi instruction with an opcode !=0 is executed on such a kernel? Does it produce a signal? I ask because I’d like to trap it.
The code that fields
swiinstructions is here: http://lxr.linux.no/linux+*/arch/arm/kernel/entry-common.S#L335. I am not an ARM expert, but it appears that the CPU does not stash theswiargument anywhere the kernel can get at it; if the kernel wants to know, it has to fetch the instruction from the calling program’s runtime image. This makes every system call more expensive, so (if I’m reading things correctly) the kernel only bothers to find out what theswiargument is if it’s compiled withCONFIG_OABI_COMPAT.EDIT: The ARM ARM confirms that SWI does not do anything useful with its argument. (Physical page 634 / logical page A7-118.)