FDPIC/ePIC draft specification and work plan #429
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| NOTE: This style of function descriptor is used in specialized FDPIC ABIs for | ||
| Blackfin, FR-V, SuperH, and Arm, and is part of the default ABI for PA-RISC, | ||
| POWER (v1 only, has a third "static chain" field), and IA-64. |
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In PPC64 ELFv1, "static chain" is for dynamic linker's lazy binding. This is "environment pointer"?
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I think the two terms are interchangeable; they both go into r11 anyway. x86-64 also calls the register static chain.
| In ePIC, `gp` is invariant and holds the GOT address for the process image at | ||
| all instruction boundries. | ||
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| == Range extension thunks |
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This seems to belong to another proposal?
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There's another proposal to add it to the non-FDPIC ABI but it's considered an integral part of the FDPIC ABI.
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| === riscv-toolchain-conventions | ||
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| Add -mfdpic option for FDPIC and -mepic option for ePIC. |
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I think -mepic in the previous proposal is in spirit identical to -msep-data (m68k, bfin) and -mno-pic-data-is-text-relative (arm).
-fPIE -mfdpic with hidden visibility declarations can replace -fPIE -msep-data, though setting the call-clobbered FDPIC register has slight overhead.
Do we want to introduce another option to avoid the minor FDPIC register overhead?
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You're saving two memory accesses on a generic function call. It's probably close to -fomit-frame-pointer in total.
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Ping, @sorear do you have further update on this, or do you need some help on PoC implementation? |
This needs extensive editing to match the existing document, and I also haven't even started on prototype coding, but it's become clear the specification needs to exist somewhere other than my answers to questions on IRC so let's start a draft here.
I intend to create a second PR when I have something ready for formal review. Feel free to use this as a discussion thread for the high-level design.