MIPS -- add fp register; support for lwl, beqz and sltiu instructions

[matteius]

Your checklist for this pull request

• [X] I've read the guidelines for contributing to this repository
• [X] I made sure to follow the project's coding style
• [ ] I've documented or updated the documentation of every function and struct this PR changes. If not so I've explained why.
• [X] I've added tests that prove my fix is effective or that my feature works (if possible)
• [ ] I've updated the rizin book with the relevant information (if needed)

Detailed description

• In MIPS assembly language, fp stands for "frame pointer." It is a register used for stack frame management, particularly in functions that need to allocate space on the stack for local variables or save the state of other registers.
• Add support for instructions:
• lwl - load word left, The lwl instruction loads a word (4 bytes) from memory into a register. It loads the left-most (most significant) bytes of the word from memory, starting at a specified address and continuing to the next aligned word boundary.
• beqz - branch if equal zero, The beqz instruction is a pseudo-instruction in MIPS assembly, which branches to a specified address if the value in a given register is zero. It is equivalent to beq $zero, rs, offset.
• sltiu - Set Less Than Immediate Unsigne, The sltiu instruction sets a register to 1 if the value in a source register is less than an immediate value, when both are treated as unsigned integers. Otherwise, it sets the register to 0.

Also two quality of life improvements:

• When the exported lw command (from another program) is missing the offset, we can assume offset of 0 and this lets us read that back in without manually adding a 0 offset in the assembly.
• The purpose of adding the condition || (p[0] == '$' && !strcmp(p + 1, regs[n])) in the getreg function is to handle both formats of register names that are common in assembly language. In MIPS assembly, registers can be referred to either by their name (e.g., v0, s3) or by their name prefixed with a dollar sign (e.g., $v0, $s3).

Test plan

I am using this code to insert instructions via cutter, and so I get console errors whenever I encounter something that cannot be assembled.

Closing issues

Maybe closes #4509 assuming the tests get run by default by existing in that directory.

[matteius]

Thanks for taking a look @wargio and @XVilka -- I didn't quite understand:

If you want to check both disassembly and assembly, you will need to use da in asm tests

[XVilka]

Lines should start not from d instruction but from da instruction, then it will check the both ways - disassembly and assembly.

[wargio]

For clarity, please check also https://github.com/rizinorg/rizin/tree/dev/test#writing-assembly-tests

[matteius]

I will look into the test failures more later on when I have more time, thanks!

[wargio]

looks like an endianness issue.

[wargio]

i'm ok for the assembly

[XVilka]

@matteius could you please convert "da" to just "a", so that only assembly is checked, and we will merge if tests pass?Note though, some assembly tests also produce errors, please take a look at these failure as well.

[matteius]

I expect the tests will fail again; I only changed to test just assembly, but I spent a bit of time trying to run the tests locally and couldn't. I was able to build rizin, and then I did:

(base) matteius@matteius-3-0:~/rizin/test$ ../build/binrz/rz-test/rz-test db/esil/mips_32 
...
exec: Permission denied

I tried also as sudo, but that gets that exec is not found.

[wargio]

since i'm updating the mips code, i can also integrate these changes into rizin.