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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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120 changes: 69 additions & 51 deletions library/core/src/ffi/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -92,58 +92,76 @@ pub type c_ssize_t = isize;
mod c_char_definition {
cfg_if! {
// These are the targets on which c_char is unsigned.
if #[cfg(any(
all(
target_os = "linux",
any(
target_arch = "aarch64",
target_arch = "arm",
target_arch = "hexagon",
target_arch = "powerpc",
target_arch = "powerpc64",
target_arch = "s390x",
target_arch = "riscv64",
target_arch = "riscv32",
target_arch = "csky"
)
// These should match the Clang's defaults, except when Clang does not match the ABI's defaults.
//
// aarch64:
// Section 10 "Arm C and C++ language mappings" in Procedure Call Standard for the Arm®
// 64-bit Architecture (AArch64) says C/C++ char is unsigned byte.
// https://github.com/ARM-software/abi-aa/blob/2024Q3/aapcs64/aapcs64.rst#arm-c-and-c-language-mappings
// arm:
// Section 8 "Arm C and C++ Language Mappings" in Procedure Call Standard for the Arm®
// Architecture says C/C++ char is unsigned byte.
// https://github.com/ARM-software/abi-aa/blob/2024Q3/aapcs32/aapcs32.rst#arm-c-and-c-language-mappings
// csky:
// Section 2.1.2 "Primary Data Type" in C-SKY V2 CPU Applications Binary Interface
// Standards Manual says ANSI C char is unsigned byte.
// https://github.com/c-sky/csky-doc/blob/9f7121f7d40970ba5cc0f15716da033db2bb9d07/C-SKY_V2_CPU_Applications_Binary_Interface_Standards_Manual.pdf
// Note: this doesn't seem to match Clang's default (https://github.com/rust-lang/rust/issues/129945).
// hexagon:
// Section 3.1 "Basic data type" in Qualcomm Hexagon™ Application
// Binary Interface User Guide says "By default, the `char` data type is unsigned."
// https://docs.qualcomm.com/bundle/publicresource/80-N2040-23_REV_K_Qualcomm_Hexagon_Application_Binary_Interface_User_Guide.pdf
// msp430:
// Section 2.1 "Basic Types" in MSP430 Embedded Application Binary
// Interface says "The char type is unsigned by default".
// https://www.ti.com/lit/an/slaa534a/slaa534a.pdf
// Note: this doesn't seem to match Clang's default (https://github.com/rust-lang/rust/issues/129945).
// powerpc/powerpc64:
// - PPC32 SysV: "Table 3-1 Scalar Types" in System V Application Binary Interface PowerPC
// Processor Supplement says ANSI C char is unsigned byte
// https://refspecs.linuxfoundation.org/elf/elfspec_ppc.pdf
// - PPC64 ELFv1: Section 3.1.4 "Fundamental Types" in 64-bit PowerPC ELF Application
// Binary Interface Supplement 1.9 says ANSI C is unsigned byte
// https://refspecs.linuxfoundation.org/ELF/ppc64/PPC-elf64abi.html#FUND-TYPE
// - PPC64 ELFv2: Section 2.1.2.2 "Fundamental Types" in 64-Bit ELF V2 ABI Specification
// says char is unsigned byte
// https://openpowerfoundation.org/specifications/64bitelfabi/
// - AIX: XL C for AIX Language Reference says "By default, char behaves like an unsigned char."
// https://www.ibm.com/docs/en/xl-c-aix/13.1.3?topic=specifiers-character-types
// riscv32/riscv64:
// C/C++ type representations section in RISC-V Calling Conventions
// page in RISC-V ELF psABI Document says "char is unsigned."
// https://github.com/riscv-non-isa/riscv-elf-psabi-doc/blob/draft-20240829-13bfa9f54634cb60d86b9b333e109f077805b4b3/riscv-cc.adoc#cc-type-representations
// s390x:
// - ELF: "Table 1.1.: Scalar types" in ELF Application Binary Interface s390x Supplement
// Version 1.6.1 categorize ISO C char in unsigned integer
// https://github.com/IBM/s390x-abi/releases/tag/v1.6.1
// - z/OS: XL C/C++ Language Reference says: "By default, char behaves like an unsigned char."
// https://www.ibm.com/docs/en/zos/3.1.0?topic=specifiers-character-types
//
// On the following systems, c_char is signed by default, regardless of architecture.
// Darwin (macOS, iOS, etc.):
// Apple targets' c_char is signed by default even on arm
// https://developer.apple.com/documentation/xcode/writing-arm64-code-for-apple-platforms#Handle-data-types-and-data-alignment-properly
// Windows:
// Windows MSVC C++ Language Reference says "Microsoft-specific: Variables of type char
// are promoted to int as if from type signed char by default, unless the /J compilation
// 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

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@taiki-e taiki-e Dec 17, 2024 •
edited
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This is for readability in case there are more “exception targets”.

See rust-lang/libc#4198 (comment) for more.

any(
target_arch = "aarch64",
target_arch = "arm",
target_arch = "csky",
target_arch = "hexagon",
target_arch = "msp430",
target_arch = "powerpc",
target_arch = "powerpc64",
target_arch = "riscv32",
target_arch = "riscv64",
target_arch = "s390x",
),
all(target_os = "android", any(target_arch = "aarch64", target_arch = "arm")),
all(target_os = "l4re", target_arch = "x86_64"),
all(
any(target_os = "freebsd", target_os = "openbsd", target_os = "rtems"),
any(
target_arch = "aarch64",
target_arch = "arm",
target_arch = "powerpc",
target_arch = "powerpc64",
target_arch = "riscv64"
)
),
all(
target_os = "netbsd",
any(
target_arch = "aarch64",
target_arch = "arm",
target_arch = "powerpc",
target_arch = "riscv64"
)
),
all(
target_os = "vxworks",
any(
target_arch = "aarch64",
target_arch = "arm",
target_arch = "powerpc64",
target_arch = "powerpc"
)
),
all(
target_os = "fuchsia",
any(target_arch = "aarch64", target_arch = "riscv64")
),
all(target_os = "nto", target_arch = "aarch64"),
target_os = "horizon",
target_os = "aix",
))] {
pub type c_char = u8;
} else {
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