Messages in this thread | | | Date | Tue, 25 Jan 2011 12:45:24 +0000 | From | Russell King - ARM Linux <> | Subject | Re: questions about arm trustzone |
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On Tue, Jan 25, 2011 at 12:24:13PM +0000, Dave Martin wrote: > Avoiding this complexity is one of the motivations for using r7 for > the syscall number with CONFIG_EABI (instead of using the SVC comment > field).
Your history is not entirely correct.
I had the kernel side of Thumb userspace support in place long before EABI came along. Thumb doesn't have a large enough comment field to store the Linux syscall number, so to get around that problem, I decided to use r7 for the syscall number. You'll find 2.4 kernels support Thumb instructions in userspace.
As part of the EABI switch for ARM mode - which created an incompatible SWI interface anyway, we decided that we could reduce data cache pollution by eliminating the read of the SWI instruction, so we adopted the r7 method for ARM EABI mode.
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