Get undefined reference to `debug_lower_hex` when using alloc crate

[jonathanbcarlson]

• I've gotten code using core to run on the arc-elf32 target using rustc_codegen_gcc (as discussed in a Rust forum post)
• I'm attempting to link C code which calls a Rust library that allocates on the heap by running arc-elf32-gcc lib.o example.c but am getting an undefined reference to core[47ee6e850c258048]::fmt::Formatter>::debug_lower_hex
• The rust code successfully compiles using rustc example.rs --emit=obj -o lib.o --crate-type=lib -O
• If I instead compile with --crate-type=cdylib or dylib I get dropping unsupported crate type cdylib for target
• If I compile with --crate-type=staticlib then I get

  error: no global memory allocator found but one is required; link to std or add `#[global_allocator]` to a static item that implements the GlobalAlloc trait
  error: `#[panic_handler]` function required, but not found
  

• After implementing a global memory allocator by following embedded-alloc and specifying a panic handler similar to global_alloc.rs, I still get an undefined reference to debug_lower_hex.

code

// example.rs which becomes lib.o
#![no_std]

extern crate alloc;
use alloc::vec::Vec;

#[no_mangle]
pub extern "C" fn rust() -> i32 {
    let y = 42;
    let mut vec = Vec::new();
    vec.push(y);
    vec.pop().unwrap()
}

// example.c
#include <stdint.h>
#include <stdarg.h>

int32_t rust(void);

int main()
{
    printf("from rust get value %d", rust());
}

full error output

/opt/arc/lib/gcc/arc-elf32/10.2.0/../../../../arc-elf32/bin/ld: /opt/arc/lib/gcc/arc-elf32/10.2.0/../../../../arc-elf32/bin/ld: DWARF error: can't find .debug_ranges section.
src/lib.o: in function `_RNvXsP_NtCs6aT7ng1d0qi_4core3fmtRjNtB5_5Debug3fmtCsZt7r1wRFCo_4test':
fake.c:(.text._RNvXsP_NtCs6aT7ng1d0qi_4core3fmtRjNtB5_5Debug3fmtCsZt7r1wRFCo_4test+0xa): undefined reference to `_RNvMs5_NtCs6aT7ng1d0qi_4core3fmtNtB5_9Formatter15debug_lower_hex'
/opt/arc_tools_202009rel/lib/gcc/arc-elf32/10.2.0/../../../../arc-elf32/bin/ld: fake.c:(.text._RNvXsP_NtCs6aT7ng1d0qi_4core3fmtRjNtB5_5Debug3fmtCsZt7r1wRFCo_4test+0xa): undefined reference to `_RNvMs5_NtCs6aT7ng1d0qi_4core3fmtNtB5_9Formatter15debug_lower_hex'
/opt/arc_tools_202009rel/lib/gcc/arc-elf32/10.2.0/../../../../arc-elf32/bin/ld: GOT and PLT relocations cannot be fixed with a non dynamic linker
/opt/arc_tools_202009rel/lib/gcc/arc-elf32/10.2.0/../../../../arc-elf32/bin/ld: final link failed: bad value
collect2: error: ld returned 1 exit status

demangled

src/lib.o: in function `<&usize as core[47ee6e850c258048]::fmt::Debug>::fmt':
fake.c:(.text.<&usize as core[47ee6e850c258048]::fmt::Debug>::fmt+0xa): undefined reference to `<core[47ee6e850c258048]::fmt::Formatter>::debug_lower_hex'
/opt/arc_tools/lib/gcc/arc-elf32/10.2.0/../../../../arc-elf32/bin/ld: fake.c:(.text.<&usize as core[47ee6e850c258048]::fmt::Debug>::fmt+0xa): undefined reference to `<core[47ee6e850c258048]::fmt::Formatter>::debug_lower_hex'