Add support for relocations #39
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Hmm… looking at this code, I am now inclined to re-read Stephen Kell's The Missing Link, much more carefully this time. |
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This commit add `AcDSLCodeObject >> exports` that return symbols "exported" by this code object, that is, a dictionary mapping exported symbol to its address (respecting object's base address). Each exported symbol must be paired with corresponding label in instructions sequence. To export a symbol, `AcDSLAssembler` provides method `global: symbol` just like GNU assembler has .global directive [1]. [1]: https://sourceware.org/binutils/docs/as/Global.html
This commit adds basic support for relocation entries. Each processor instruction can have a relocation entry. A relocation entry is a subclass of `AcRelocation` (one subclass per relocation type) and contains a (relocatable) symbol. Particular relocation type (a concrete subclass of `AcRelocation`) is valid only for some instructions (`#isValidForInstruction`) and knows how to fixup (patch) that instruction, knowing the final address of its symbol (note, that this final address might be address of trampoline or into address table if final address is beyond the maximum displacement). In some cases, relocation entries must come in pairs (like %lo must follow %hi). Currently, there's no way to ensure nor validate that - this is user's responsibility.
This commit adds relocation support to DSL assembler. To to relocate
an operand, use `relocation_type % operand`, for example:
asm auipc: ra, ra, R_RISCV_PCREL_HI20 % label
This commit adds pool with `*_MIN` and `*_MAX` values for fixed-length integers (both signed and unsigned). Using them rather than integer literals improve readability.
This commit adds pool containing various constants related to RISC-V ISAm such as bit-size of immediates, min / max values of those and so on to improve readability of code.
This commit add basic support for GOT accesses. During relocation
processing (linking) a relocation may request GOT entry for its symbol
by
gotentry := AcRelocationRequestGOTEntry query: self
The response (`gotentry` in the above example) is an association from
GOT entry symbol to its address (that is, address of the entry). Actual
allocation of GOT entries is the responsibility of the linker.
This commit add basic support for PLT calls, using similar mechanism as for GOT entries introduced in previous commit.
This commit adds `R_RISCV_GOT_HI20` relocation class and fixes `R_RISCV_PCREL_LO12_*` to also work with it. This allows consumers to generate GOT access for external symbols.
This commit add simple example showing how to use relocations when using DSL assembler.
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This PR adds basic support for relocations.
At the moment, this PR is work in progress. I'm still not 100% happy with it - design wise - but this should be enough to enable further experiments with TR and AoT withing ST25.
One thing that is probably missing is to add proper support for code object sections, so compiler can for example produce jump table for PICs in "data" section or big constants or global variable addresses in "rodata".
Once finalized, this would probably need to be split into 2 or three smallter PRs.