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Fix c_char on various no-std and tier 3 targets #131319

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Fix c_char on various no-std and tier 3 targets #131319

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@taiki-e taiki-e commented Oct 6, 2024 •
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Fixes #129945

there are many target_os = "none" target and tier3 targets that do not match.

  • As for the target_os = "none" target, most of them probably do not match with Clang's default.
    • I guess this is because c_char was originally defined in std and this mismatch was missed when it was moved to core.
    • I don't think many people use c_char directly on these targets, but this includes a lot of tier 2 targets, so changing this to match Clang could have a not small impact on embedded ecosystem.
  • All other targets seem to be tier 3, so I think changing them to match Clang's default should be no problem.
    • However, note that Clang's default may be wrong for minor architectures such as C-SKY. (see the reference below)

On MSP430 (tier 3), both Clang and rustc don't match with the ABI's default char type...

This PR makes c_char match with the Clang's default, except when Clang does not match the ABI's default.

TODO:

r? @ghost

@rustbot label -S-waiting-on-review, +S-waiting-on-author

@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Oct 6, 2024
@taiki-e taiki-e force-pushed the c-char branch 2 times, most recently from 38245fc to f587fe3 Compare October 7, 2024 15:44
@rustbot rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Oct 12, 2024
@workingjubilee workingjubilee added the A-ABI Area: Concerning the application binary interface (ABI) label Oct 21, 2024
kadiwa4
kadiwa4 reviewed Oct 27, 2024
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library/core/src/ffi/mod.rs
// option is used."
// https://learn.microsoft.com/en-us/cpp/cpp/fundamental-types-cpp?view=msvc-170#character-types)
if #[cfg(all(
not(any(target_vendor = "apple", windows)),
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Suggested change
not(any(target_vendor = "apple", windows)),
not(target_vendor = "apple"),
not(windows),

would be easier to understand IMO

@tgross35 tgross35 mentioned this pull request Nov 15, 2024
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arichardson added a commit to arichardson/rust that referenced this pull request Dec 10, 2024
@arichardson @taiki-e
Add references to the specific ABI documents
dd3e98c 
Expcept for L4RE and Xtensa these were obtained from rust-lang#131319

I could not find an open link to the Xtensa documentation, but the
signedness was confirmed by on of the Xtensa developers in
llvm/llvm-project#115967 (comment)

Co-authored-by: Taiki Endo <[email protected]>
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kadiwa4 commented Dec 11, 2024 •
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This is being superseded by #132975 now

@bors bors closed this in fe516ef Dec 11, 2024
rust-timer added a commit to rust-lang-ci/rust that referenced this pull request Dec 11, 2024
@rust-timer
Unrolled build for rust-lang#132975
e8ae496 
Rollup merge of rust-lang#132975 - arichardson:ffi-c-char, r=tgross35

De-duplicate and improve definition of core::ffi::c_char

Instead of having a list of unsigned char targets for each OS, follow the logic Clang uses and instead set the value based on architecture with a special case for Darwin and Windows operating systems. This makes it easier to support new operating systems targeting Arm/AArch64 without having to modify this config statement for each new OS. The new list does not quite match Clang since I noticed a few bugs in the Clang implementation (llvm/llvm-project#115957).

Fixes rust-lang#129945
Closes rust-lang#131319
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c_char signedness doesn't match with Clang's default on various no-std and tier 3 targets
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