Hi, This small patch series adds semihosting support for the MIPS target. The API has been originally set with the SDE toolchain from Algorithmics, and has been used with bare-metal software meant to be debugged with JTAG hardware and simulators using the MDI API [1][2]. It also uses the name of `_mdi_syscall' for its entry point. Therefore it has been commonly referred to as "MDI semihosting".
Despite that the semihosting API has nothing specific to MDI in it and can be implemented in any bare-metal debugging environment such as QEMU. I decided to keep the name throughout this submission to preserve the tradition and for people who know what this is all about to recognise it immediately. The MDI semihosting API has to the best of my knowledge never been formally documented. Calls are requested by the program run on the target by calling the magic `_mdi_syscall' entry point, as defined by the symbol table and also stored in a magic `.sdeosabi' section. Reaching that point is supposed to be intercepted with a breakpoint and processor registers interpreted as follows: - $v0 -- request number, - $a0-$a2 -- arguments, - $ra -- return address. Upon completion results are set as follows: - $v0 -- request result, negative if unsuccessful, - $v1 -- error number, - $pc -- set to input $ra, except for the `exit' request that does not return and the `gettime' request that uses $v0-$v1 to return a pair of results. Execution is then resumed. This code has been originally submitted, as recorded here: http://lists.nongnu.org/archive/html/qemu-devel/2009-07/msg01487.html by Nathan Froyd, who has since left the company. This version extends the original implementation by adding 64-bit support. It has been tested by running the GDB test suite against it, with QEMU in the system emulation mode specified as the remote target to talk to for individual test cases (`target remote | qemu-system ...'). The toolchain has been configured for the mips-sde-elf target (bare metal, with newlib as the C library and our CS3 low-level runtime) and the following multilibs were tested: -EB -EB -mabi=64 to cover both 32-bit and 64-bit support. Results were as follows, respectively: Result Count ERROR 15 FAIL 4 PASS 16646 XPASS 40 XFAIL 152 KFAIL 52 UNTESTED 79 UNRESOLVED 15 UNSUPPORTED 219 Total 17222 and: Result Count ERROR 28 FAIL 1 PASS 16469 XPASS 23 XFAIL 118 KFAIL 52 UNTESTED 78 UNRESOLVED 28 UNSUPPORTED 220 Total 17017 References: [1] "The Meta Debug Interface (MDI)", Mentor Graphics Corporation, Revision 1.2, Monday, December 20, 2010 [2] "Microprocessor Debug Interface (MDI) Specification", MIPS Technologies, Inc., Document Number: MD00412, Revision 02.41, September 22, 2009 Maciej
