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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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‎core/src/ffi/mod.rs

+80-53
Original file line numberDiff line numberDiff line change
@@ -91,59 +91,86 @@ pub type c_ssize_t = isize;
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mod c_char_definition {
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cfg_if! {
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// These are the targets on which c_char is unsigned.
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if #[cfg(any(
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all(
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target_os = "linux",
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any(
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target_arch = "aarch64",
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target_arch = "arm",
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target_arch = "hexagon",
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target_arch = "powerpc",
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target_arch = "powerpc64",
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target_arch = "s390x",
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target_arch = "riscv64",
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target_arch = "riscv32",
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target_arch = "csky"
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)
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),
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all(target_os = "android", any(target_arch = "aarch64", target_arch = "arm")),
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all(target_os = "l4re", target_arch = "x86_64"),
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all(
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any(target_os = "freebsd", target_os = "openbsd", target_os = "rtems"),
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any(
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target_arch = "aarch64",
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target_arch = "arm",
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target_arch = "powerpc",
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target_arch = "powerpc64",
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target_arch = "riscv64"
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)
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),
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all(
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target_os = "netbsd",
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any(
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target_arch = "aarch64",
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target_arch = "arm",
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target_arch = "powerpc",
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target_arch = "riscv64"
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)
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),
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all(
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target_os = "vxworks",
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any(
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target_arch = "aarch64",
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target_arch = "arm",
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target_arch = "powerpc64",
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target_arch = "powerpc"
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)
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),
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all(
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target_os = "fuchsia",
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any(target_arch = "aarch64", target_arch = "riscv64")
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),
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all(target_os = "nto", target_arch = "aarch64"),
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target_os = "horizon",
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target_os = "aix",
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// These are the targets on which c_char is unsigned. Usually the
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// signedness is the same for all target_os values on a given architecture
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// but there are some exceptions (see isSignedCharDefault() in clang).
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//
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// aarch64:
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// Section 10 "Arm C and C++ language mappings" in Procedure Call Standard for the Arm®
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// 64-bit Architecture (AArch64) says C/C++ char is unsigned byte.
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// https://github.com/ARM-software/abi-aa/blob/2024Q3/aapcs64/aapcs64.rst#arm-c-and-c-language-mappings
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// arm:
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// Section 8 "Arm C and C++ Language Mappings" in Procedure Call Standard for the Arm®
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// Architecture says C/C++ char is unsigned byte.
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// https://github.com/ARM-software/abi-aa/blob/2024Q3/aapcs32/aapcs32.rst#arm-c-and-c-language-mappings
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// csky:
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// Section 2.1.2 "Primary Data Type" in C-SKY V2 CPU Applications Binary Interface
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// Standards Manual says ANSI C char is unsigned byte.
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// https://github.com/c-sky/csky-doc/blob/9f7121f7d40970ba5cc0f15716da033db2bb9d07/C-SKY_V2_CPU_Applications_Binary_Interface_Standards_Manual.pdf
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// Note: this doesn't seem to match Clang's default (https://github.com/rust-lang/rust/issues/129945).
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// hexagon:
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// Section 3.1 "Basic data type" in Qualcomm Hexagon™ Application
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// Binary Interface User Guide says "By default, the `char` data type is unsigned."
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// https://docs.qualcomm.com/bundle/publicresource/80-N2040-23_REV_K_Qualcomm_Hexagon_Application_Binary_Interface_User_Guide.pdf
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// msp430:
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// Section 2.1 "Basic Types" in MSP430 Embedded Application Binary
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// Interface says "The char type is unsigned by default".
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// https://www.ti.com/lit/an/slaa534a/slaa534a.pdf
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// Note: this doesn't seem to match Clang's default (https://github.com/rust-lang/rust/issues/129945).
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// powerpc/powerpc64:
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// - PPC32 SysV: "Table 3-1 Scalar Types" in System V Application Binary Interface PowerPC
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// Processor Supplement says ANSI C char is unsigned byte
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// https://refspecs.linuxfoundation.org/elf/elfspec_ppc.pdf
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// - PPC64 ELFv1: Section 3.1.4 "Fundamental Types" in 64-bit PowerPC ELF Application
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// Binary Interface Supplement 1.9 says ANSI C is unsigned byte
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// https://refspecs.linuxfoundation.org/ELF/ppc64/PPC-elf64abi.html#FUND-TYPE
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// - PPC64 ELFv2: Section 2.1.2.2 "Fundamental Types" in 64-Bit ELF V2 ABI Specification
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// says char is unsigned byte
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// https://openpowerfoundation.org/specifications/64bitelfabi/
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// - AIX: XL C for AIX Language Reference says "By default, char behaves like an unsigned char."
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// https://www.ibm.com/docs/en/xl-c-aix/13.1.3?topic=specifiers-character-types
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// riscv32/riscv64:
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// C/C++ type representations section in RISC-V Calling Conventions
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// page in RISC-V ELF psABI Document says "char is unsigned."
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// https://github.com/riscv-non-isa/riscv-elf-psabi-doc/blob/draft-20240829-13bfa9f54634cb60d86b9b333e109f077805b4b3/riscv-cc.adoc#cc-type-representations
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// s390x:
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// - ELF: "Table 1.1.: Scalar types" in ELF Application Binary Interface s390x Supplement
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// Version 1.6.1 categorize ISO C char in unsigned integer
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// https://github.com/IBM/s390x-abi/releases/tag/v1.6.1
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// - z/OS: XL C/C++ Language Reference says: "By default, char behaves like an unsigned char."
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// https://www.ibm.com/docs/en/zos/3.1.0?topic=specifiers-character-types
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// Xtensa:
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// - "The char type is unsigned by default for Xtensa processors."
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//
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// On the following operating systems, c_char is signed by default, regardless of architecture.
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// Darwin (macOS, iOS, etc.):
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// Apple targets' c_char is signed by default even on arm
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// https://developer.apple.com/documentation/xcode/writing-arm64-code-for-apple-platforms#Handle-data-types-and-data-alignment-properly
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// Windows:
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// Windows MSVC C++ Language Reference says "Microsoft-specific: Variables of type char
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// are promoted to int as if from type signed char by default, unless the /J compilation
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// option is used."
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// https://learn.microsoft.com/en-us/cpp/cpp/fundamental-types-cpp?view=msvc-170#character-types)
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// L4RE:
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// The kernel builds with -funsigned-char on all targets (but useserspace follows the
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// architecture defaults). As we only have a target for userspace apps so there are no
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// special cases for L4RE below.
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if #[cfg(all(
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not(windows),
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not(target_vendor = "apple"),
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any(
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target_arch = "aarch64",
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target_arch = "arm",
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target_arch = "csky",
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target_arch = "hexagon",
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target_arch = "msp430",
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target_arch = "powerpc",
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target_arch = "powerpc64",
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target_arch = "riscv64",
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target_arch = "riscv32",
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target_arch = "s390x",
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target_arch = "xtensa",
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)
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))] {
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pub type c_char = u8;
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} else {

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