The primary purpose of these changes is to support programs compiled by GCC for the R5900 target and thereby run R5900 Linux distributions, for example Gentoo.
GCC in version 7.3, by itself, by inspection of the GCC source code and inspection of the generated machine code, for the R5900 target, only emits two instructions that are specific to the R5900: the three- operand MULT and MULTU. GCC and libc also emit certain MIPS III instructions that are not part of the R5900 ISA. They are normally trapped and emulated by the Linux kernel, and therefore need to be treated accordingly by QEMU. This is addressed, in turn, by the patch series. A program compiled by GCC is taken to mean source code compiled by GCC under the restrictions above. One can, with the apparent limitations, with a bit of effort obtain a fully functioning operating system such as R5900 Gentoo. Strictly speaking, programs need not be compiled by GCC to make use of this change. Instructions and other facilities of the R5900 not implemented by these changes are intended to signal provisional exceptions. One such example is the FPU that is not compliant with IEEE 754-1985 in system mode. It is therefore provisionally disabled. In user space the FPU is trapped and emulated by IEEE 754-1985 compliant software in the kernel, and this is handled accordingly by QEMU. Another example is the 93 multimedia instructions specific to the R5900 that generate provisional reserved instruction exception signals. One of the benefits of running a Linux distribution under QEMU is that programs can be compiled with a native compiler, where the host and target are the same, as opposed to a cross-compiler, where they are not the same. This is especially important in cases where the target hardware does not have the resources to run a native compiler. Problems with cross-compilation are often related to host and target differences in integer sizes, pointer sizes, endianness, machine code, ABI, etc. Sometimes cross-compilation is not even supported by the build script for a given package. One effective way to avoid those problems is to replace the cross-compiler with a native compiler. This change of compilation methods does not resolve the inherent problems with cross-compilation. The native compiler naturally replaces the cross-compiler, because one typically uses one or the other, and preferably the native compiler when the circumstances admit this. The native compiler is also a good test case for the R5900 QEMU user mode. Additionally, Gentoo is well- known for compiling and installing its packages from sources. This change has been tested with Gentoo compiled for R5900, including native compilation of several packages under QEMU. I used the Gentoo sys-devel/crossdev package https://wiki.gentoo.org/wiki/Crossdev with patches mainly to simplify the handling of LL/SC and floating point support, to avoid complications with additional configure and compiler flags. Busybox https://busybox.net/ can also be used to build a simple functional R5900 program. It can be used to test the R5900 CPU in QEMU user mode. The R5900 implements the 64-bit MIPS III instruction set except DMULT, DMULTU, DDIV, DDIVU, LL, SC, LLD and SCD. The MIPS IV instructions MOVN, MOVZ and PREF are implemented. It has the R5900 specific three-operand instructions MADD, MADDU, MULT and MULTU as well as pipeline 1 versions MULT1, MULTU1, DIV1, DIVU1, MADD1, MADDU1, MFHI1, MFLO1, MTHI1 and MTLO1. A set of 93 128-bit multimedia instructions specific to the R5900 is also implemented. The Toshiba TX System RISC TX79 Core Architecture manual http://www.lukasz.dk/files/tx79architecture.pdf describes the C790 processor that is a follow-up to the R5900. There are a few notable differences in that the R5900 FPU - is not IEEE 754-1985 compliant, - does not implement double format, and - its machine code is nonstandard. Changes in v6: - Set the CP0 PRId implementation number to 0x2E for the R5900 - Refer to the C790 follow-up in the definition of the R5900 - Define and use check_insn_opc_user_only in the same change - Rename gen_mul_r5900 to gen_mul_txxx - Enclose single statements in braces - Expand and reword commit messages and notes - Reword the cover letter subject line - All changes build with GCC and Clang - Approval from checkpatch.pl Changes in v5: - Reorder check_insn_opc_user_only calls - Call check_insn_opc_removed in check_insn_opc_user_only Changes in v4: - Split into a patch series consting of eight changes - Expand commit messages and notes - Introduce check_insn_opc_user_only - Base R5900 on MIPS III, with MOVN, MOVZ and PREF from MIPS IV - DMULT, DMULTU, DDIV, DDIVU, LL, SC, LLD and SCD are user only - Note Toshiba/Sony R5900 for EF_MIPS_MACH_R5900 definition - Rework gen_mul_r5900 - Fix ICE and DCE - Fix SEGBITS and PABITS - Fix indentation Changes in v3: - Apply to HEAD - Remove the word "initial" from subject line Changes in v2: - Update mips_defs array with R5900 values - LL/SC and FPU are user only Fredrik Noring (7): target/mips: Define R5900 instructions and CPU preprocessor constants target/mips: Support R5900 specific three-operand MULT and MULTU target/mips: Support R5900 instructions MOVN, MOVZ and PREF from MIPS IV target/mips: R5900 DMULT[U], DDIV[U], LL[D] and SC[D] are user only target/mips: Define the R5900 CPU linux-user/mips: Recognise the R5900 CPU model elf: Toshiba/Sony rather than MIPS are the implementors of the R5900 include/elf.h | 2 +- linux-user/mips/target_elf.h | 3 ++ target/mips/mips-defs.h | 2 + target/mips/translate.c | 101 +++++++++++++++++++++++++++++++++++++-- target/mips/translate_init.inc.c | 59 +++++++++++++++++++++++ 5 files changed, 163 insertions(+), 4 deletions(-) -- 2.16.4
