Switch to cdylibs

[geofft]

This seems like the right thing to do (cf. Rust RFC 1510) but when I tried it it didn't export my hook function.

$ nm -D examples/readlinkspy/target/debug/libreadlinkspy.so
                 w __cxa_finalize
                 w __gmon_start__
                 w _ITM_deregisterTMCloneTable
                 w _ITM_registerTMCloneTable
                 w _Jv_RegisterClasses
00000000000009d0 T rust_eh_personality
                 U _Unwind_GetDataRelBase
                 U _Unwind_GetIPInfo
                 U _Unwind_GetLanguageSpecificData
                 U _Unwind_GetRegionStart
                 U _Unwind_GetTextRelBase
                 U _Unwind_SetGR
                 U _Unwind_SetIP

[milahu]

it didn't export my hook function

same, but it works with LD_PRELOAD

symbol count, as reported by nm
3139 dylib
68 cdylib

[milahu]

redhook + crate_type = ["cdylib"] requires rust-nightly

[lib]
crate_type = ["dylib"] # works with rust-stable and rust-nightly
# release binary size
# 2.7M rust-stable
# 5.2M rust-nightly

[lib]
crate_type = ["cdylib"] # requires rust-nightly. silently fails with rust-stable
# release binary size
# 450 KB rust-nightly
#  20 KB rust-stable (broken)

compile options for my project

[profile.release]
# https://arusahni.net/blog/2020/03/optimizing-rust-binary-size.html
# https://github.com/johnthagen/min-sized-rust
opt-level = "s" # optimize for binary size
lto = true
codegen-units = 1
panic = "abort" # disable backtraces on panic