我_993644_的FFI . LLVMPrintModuleToString uses strdup to create a string . 但是，当我将指针包装在 CString 中时，Rust会丢弃它时出现错误 .
#![feature(cstr_memory)]
use std::ffi::CString;
extern crate llvm_sys as llvm;
fn main() {
let llvm_ir_cstring;
unsafe {
let module = llvm::core::LLVMModuleCreateWithName(b"nop\0".as_ptr() as *const _);
let llvm_ir_char_ptr = llvm::core::LLVMPrintModuleToString(module);
llvm::core::LLVMDisposeModule(module);
llvm_ir_cstring = CString::from_ptr(llvm_ir_char_ptr);
}
println!("llvm_ir_cstring: {:?}", llvm_ir_cstring);
}
Valgrind错误：
==10413== Invalid read of size 4
==10413== at 0x4870586: pthread_mutex_lock (in /usr/lib/libpthread-2.21.so)
==10413== by 0x17F89B: je_arena_dalloc_small (in /home/wilfred/projects/bfc/target/debug/bfc)
==10413== by 0x178C30: je_sdallocx (in /home/wilfred/projects/bfc/target/debug/bfc)
==10413== by 0x10FA57: heap::imp::deallocate::h1fb92d59333c497bkja (heap.rs:268)
==10413== by 0x10F999: heap::deallocate::h5680e3fedc9e96320da (heap.rs:89)
==10413== by 0x10F929: heap::exchange_free::h452463f962f7ec23kfa (heap.rs:131)
==10413== by 0x10F8C5: Box$LT$$u5b$u8$u5d$$GT$::drop.1769::haf7017472635c7cf (in /home/wilfred/projects/bfc/target/debug/bfc)
==10413== by 0x10F836: std..ffi..c_str..CString::drop.1766::h04d2b3db8d468f0c (in /home/wilfred/projects/bfc/target/debug/bfc)
==10413== by 0x10F5FF: main::h04b7feb343e229ccgaa (in /home/wilfred/projects/bfc/target/debug/bfc)
==10413== by 0x16DBCA: rt::unwind::try::try_fn::h2403085009213705177 (in /home/wilfred/projects/bfc/target/debug/bfc)
==10413== by 0x16FF5A: rust_try_inner (in /home/wilfred/projects/bfc/target/debug/bfc)
==10413== by 0x16FF33: rust_try (in /home/wilfred/projects/bfc/target/debug/bfc)
==10413== Address 0x1d684 is not stack'd, malloc'd or (recently) free'd
为什么是这样？从C API处理 *char 的正确方法是什么？
1 回答
根据the function's documentation：
在一般情况下，如果在一个分配内存的库中调用一个函数，你应该在该库中调用另一个释放内存的函数;这通常应记录为函数 Contract 的一部分 .
如果函数的文档告诉您使用
free，那么如果您的应用程序没有与库的malloc对应的free链接，则会出现问题（例如，您的应用程序链接到msvcr120，但库链接到msvcr100） . 这就是为什么好的库提供了一种解除分配给你的资源的方法的原因 .Rust中的默认内存分配器不是C的
malloc，而是另一个名为jemalloc的分配器 .CString假设该字符串是使用Rust的内存分配器分配的，所以CString's destructor runs, it runs jemalloc' sfree（您可以从调用堆栈中的je_-prefixed函数中判断出来），但由于字符串不是't allocated with jemalloc' smalloc而失败了 .