Build failure on platforms without `<stdatomic.h>` due to use of non-standard `u_int64_t`

I am having trouble cross-compiling iperf v3.21 in julia's BinaryBuilder.jl toolchain (see https://github.com/JuliaPackaging/Yggdrasil/pull/14208). The affected platforms are:

• i686-linux-musl
• x86_64-linux-musl
• aarch64-linux-musl
• armv6l-linux-musleabihf
• armv7l-linux-musleabihf

The following writeup was written with the assistance of ChatGPT.

Description

Building iperf 3.21 fails on targets where <stdatomic.h> is not available. The failure occurs in the fallback atomic type definition in src/iperf_api.h.

The build emits the following warning and error:

../src/iperf_api.h:47:2: warning: #warning "No <stdatomic.h> available" [-Wcpp]
 #warning "No <stdatomic.h> available"

../src/iperf_api.h:48:1: error: unknown type name ‘u_int64_t’
 typedef u_int64_t atomic_uint_fast64_t;
 ^

Reproduction environment

I am building iperf 3.21 using Julia's BinaryBuilder infrastructure, which builds portable binaries across multiple target platforms.

The relevant build command is:

./configure --prefix=${prefix} --build=${MACHTYPE} --host=${target} --disable-profiling
make -j${nproc}
make install

The failure occurs during compilation of the mis component:

cc -std=gnu11 -DHAVE_CONFIG_H -I. -I../src -g -g -O2 -Wall -pthread \
   -MT mis-mis.o -MD -MP -MF .deps/mis-mis.Tpo \
   -c -o mis-mis.o mis.c

Cause

When C11 atomics are unavailable, src/iperf_api.h provides a fallback definition:

#ifndef HAVE_STDATOMIC_H
#warning "No <stdatomic.h> available"
typedef u_int64_t atomic_uint_fast64_t;
#endif

However, u_int64_t is not a standard C type. It is a BSD-derived typedef that is not guaranteed to exist on all platforms. Portable C code should use uint64_t, which is defined by <stdint.h>.

As a result, platforms without <stdatomic.h> but without BSD integer typedefs fail to compile.

Suggested fix

Replace the fallback typedef with a standard fixed-width integer type:

#ifndef HAVE_STDATOMIC_H
#warning "No <stdatomic.h> available"
#include <stdint.h>
typedef uint64_t atomic_uint_fast64_t;
#endif

Alternatively, include the appropriate header that defines u_int64_t if retaining that typedef is desired, although using uint64_t would be more portable.

Additional context

The issue does not appear on systems where either:

• <stdatomic.h> is available and the fallback code is not used, or
• system headers provide the BSD u_int64_t typedef.

It affects cross-platform builds targeting environments with limited libc headers or non-BSD-derived C libraries.

A small change to the fallback implementation should make iperf build successfully on these targets.