Incorrect translation of alloca in block scope #759
Description
Tested with c2rust 0.16.0
#include <stdio.h>
#include <string.h>
int one = 1;
int main(void) {
char *p;
if (one) {
p = __builtin_alloca(100);
}
strcpy(p, "Hello, world!");
puts(p);
}This is a program that has no memory errors. The if (one) is guaranteed to be entered, though the compiler cannot see that, and the result of __builtin_alloca persists until the function ends, even after the block has ended.
It is translated to the following Rust code:
#![allow(dead_code, mutable_transmutes, non_camel_case_types, non_snake_case, non_upper_case_globals, unused_assignments, unused_mut)]
#![register_tool(c2rust)]
#![feature(register_tool)]
use ::c2rust_out::*;
extern "C" {
fn puts(__s: *const libc::c_char) -> libc::c_int;
fn strcpy(_: *mut libc::c_char, _: *const libc::c_char) -> *mut libc::c_char;
}
#[no_mangle]
pub static mut one: libc::c_int = 1 as libc::c_int;
unsafe fn main_0() -> libc::c_int {
let mut p: *mut libc::c_char = 0 as *mut libc::c_char;
if one != 0 {
let mut fresh0 = ::std::vec::from_elem(
0,
100 as libc::c_int as libc::c_uint as usize,
);
p = fresh0.as_mut_ptr() as *mut libc::c_char;
}
strcpy(p, b"Hello, world!\0" as *const u8 as *const libc::c_char);
puts(p);
return 0;
}
pub fn main() {
unsafe { ::std::process::exit(main_0() as i32) }
}Note here the let mut fresh0 = ::std::vec::from_elem(0, 100 as libc::c_int as libc::c_uint as usize); in block scope. Here, unlike in the C program, the vec will be dropped when the block is exited, and p is left a dangling pointer.
A possible corrected translation would be to make fresh0 a function-scope variable.