Add support for LTO and remove link-dead-code #118
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Seems to work but the rustc patch needs a big rebase. |
sajattack
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Jun 8, 2022
JohnTitor
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Previously, the linker script forcefully kept all `.lib.stub` sections, unnecessarily bloating the binary. Now, the script is LTO and `--gc-sections` friendly. `--nmagic` was also added to the linker, because page alignment is not required on the PSP. This further reduces binary size. Accompanying changes for the PSP crate are found in: overdrivenpotato/rust-psp#118
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…woerister Relax mipsel-sony-psp's linker script Previously, the linker script forcefully kept all `.lib.stub` sections, unnecessarily bloating the binary. Now, the script is LTO and `--gc-sections` friendly. `--nmagic` was also added to the linker, because page alignment is not required on the PSP. This further reduces binary size. Accompanying changes for the `psp` crate are found in: overdrivenpotato/rust-psp#118
JohnTitor
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…woerister Relax mipsel-sony-psp's linker script Previously, the linker script forcefully kept all `.lib.stub` sections, unnecessarily bloating the binary. Now, the script is LTO and `--gc-sections` friendly. `--nmagic` was also added to the linker, because page alignment is not required on the PSP. This further reduces binary size. Accompanying changes for the `psp` crate are found in: overdrivenpotato/rust-psp#118
overdrivenpotato
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This is achieved by utilizing the 8 bytes of a function stub as a place to store pointers to the relevant NID and library entry struct. At runtime these are overwritten by the OS, but this link lets LLVM know not to remove those seemingly unused sections. Because this means that the number of function stubs depends on the linker output, cargo-psp has been modified to properly update the library stub count after the normal linking stage. This commit requires linker script changes in rustc; this will happen in an accompanying patch.
This greatly reduces binary sizes, at the expense of compilation speed. Normal builds still use a regular non-LTO build of libunwind.
Through testing, LLVM is not able to see past the transmute, so we effectively already have a black box. To avoid UB, this should probably be done via external linking through a different crate, though this is simpler and works well enough for this particularly constrained target.
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Before being merged, this requires an accompanying
rustcpatch, TBA soon.