Comment by jmalicki
17 days ago
All you have to do is record a table of fixup locations you can fill in in a second pass once the labels are resolved.
17 days ago
All you have to do is record a table of fixup locations you can fill in in a second pass once the labels are resolved.
In practice, one of the difficulties in getting _clang_ to assemble the Linux kernel (as opposed to GNU `as` aka GAS), was having clang implement support for "fragments" in more places.
https://eli.thegreenplace.net/2013/01/03/assembler-relaxatio...
There were a few cases IIRC around usage of the `.` operator which means something to the effect of "the current point in the program." It can be used in complex expressions, and sometimes resolving those requires multiple passes. So supporting GAS compatible syntax in more than just the basic cases forces the architecture of your assembler to be multi-pass.
I mean, no, it's more than that.
You also need to choose optimal instruction encoding, and you need to understand how relocs work - which things can you resolve now vs which require you to encode info for the linker to fill in once the program is launched, etc etc.
Not sure why I'm on this little micro-rant about this; I'm sure Claude could write a workable assembler. I'm more like.. I've written one assembler and many, many parsers, and the parsers where way simpler, yet this thread is littered with people that seem to think assemblers are just lookup tables from ascii to machine code with a loop slapped on top of them.