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doc/stdenv: hardening flags: add section on zerocallusedregs

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Robert Scott 2024-06-05 23:09:12 +01:00
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doc/stdenv/stdenv.chapter.md
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@ -1667,6 +1667,10 @@ Adds the `-fPIE` compiler and `-pie` linker options. Position Independent Execut
Static libraries need to be compiled with `-fPIE` so that executables can link them in with the `-pie` linker option.
If the libraries lack `-fPIE`, you will get the error `recompile with -fPIE`.
#### `zerocallusedregs` {#zerocallusedregs}
Adds the `-fzero-call-used-regs=used-gpr` compiler option. This causes the general-purpose registers that an architecture's calling convention considers "call-used" to be zeroed on return from the function. This can make it harder for attackers to construct useful ROP gadgets and also reduces the chance of data leakage from a function call.
[^footnote-stdenv-ignored-build-platform]: The build platform is ignored because it is a mere implementation detail of the package satisfying the dependency: As a general programming principle, dependencies are always *specified* as interfaces, not concrete implementation.
[^footnote-stdenv-native-dependencies-in-path]: Currently, this means for native builds all dependencies are put on the `PATH`. But in the future that may not be the case for sake of matching cross: the platforms would be assumed to be unique for native and cross builds alike, so only the `depsBuild*` and `nativeBuildInputs` would be added to the `PATH`.
[^footnote-stdenv-propagated-dependencies]: Nix itself already takes a package’s transitive dependencies into account, but this propagation ensures nixpkgs-specific infrastructure like [setup hooks](#ssec-setup-hooks) also are run as if it were a propagated dependency.