Different string type on aarch64-linux and everything else?

[kubukoz]

Hi! I'm trying to generate bindings for sqlite3. Using int sqlite3_open as an example.

The header is

SQLITE_API int sqlite3_open(
  const char *filename,   /* Database filename (UTF-8) */
  sqlite3 **ppDb          /* OUT: SQLite db handle */
);

(I've confirmed that the signature is the same on both ARM mac and ARM Linux)

On an ARM mac or x86 linux, I'm getting:

  /**
   * [bindgen] header: (truncated)/include/sqlite3.h
  */
  def sqlite3_open(filename : CString, ppDb : Ptr[Ptr[sqlite3]]): CInt = extern

but on ARM Linux, it's:

  /**
   * [bindgen] header: (truncated)/include/sqlite3.h
  */
  def sqlite3_open(filename : Ptr[CUnsignedChar], ppDb : Ptr[Ptr[sqlite3]]): CInt = extern

so clearly filename changes from CString to Ptr[CUnsignedChar].

Cheatsheet:

• type CString = Ptr[CChar]
• type CChar = Byte
• type CUnsignedChar = UByte

Am I doing something wrong, or could this be an issue in sn-bingen?

Note: I'm using the sn-bingen binary from the Nix flake.

[keynmol]

I've seen this before.

Bindgen by itself does not have platform specific code, it uses libclang for introspection of numeric types.

Seems like on all platforms I test on apart from arm64 linux, the implementation of what "char" means is a signed char.

The standard though doesn't specify what char means (words on SO, I didn't bother to verify: https://stackoverflow.com/a/2054941).

To enforce one way or another, you can use -fsigned-char or -funsigned-char in clang flags passed to bindgen.

I recommend using -fsigned-char as it will use CString in the bindings.

Confirmed in an arm64 VM:

$ bin/bindgen --header test.h --package sqlite --scala --clang -fsigned-char
package sqlite

import _root_.scala.scalanative.unsafe.*
import _root_.scala.scalanative.unsigned.*
import _root_.scala.scalanative.libc.*
import _root_.scala.scalanative.*


@extern
private[sqlite] object extern_functions:
  /**
   * [bindgen] header: test.h
  */
  def sqlite3_open(filename : CString): CInt = extern


object functions:
  import extern_functions.*
  export extern_functions.*


object all:
  export _root_.sqlite.functions.sqlite3_open