What's that? Okey, BusyBox is a multi call binary, one binary as ls,cat and more.

Why? Please ask the LLM for an answer.

TLDR: modify each commands' entry function to export int cmd_xxx_main(...), write a wrapper as new entry to call different cmd_xxx_main depends on argv[0], finally link them together.

Some projects like libwebp were compiled into many executabe, here's how to modify as little as possible to build it into multi call binary.

First, download and extract the source tarballs:

mkdir webp
cd webp
curl -L https://github.com/webmproject/libwebp/archive/2e81017c7a345f687223086cbc177a8459a18b52.tar.gz | tar -zx --strip-components 1 # 20240901 > 1.4.0

Then modify the entry function name by sed commands:

sed -i.bak -e 's|int main(|int cmd_webpinfo_main(|' examples/webpinfo.c
sed -i.bak -e 's|int main(|int cmd_cwebp_main(|' examples/cwebp.c
sed -i.bak -e 's|int main(|int cmd_dwebp_main(|' examples/dwebp.c

For C++, needs extern "C" to keep a stable C-ABI:

sed -i.bak -e 's|int main(|extern "C" int cmd_djxl_main(|' tools/djxl_main.cc

Then you need a wrapper, multicall.cc:

#include <stddef.h>
#include <string.h>
#include <stdio.h>
#if defined(WIN32) || defined(_WIN32)
#define PATH_SEPARATOR '\\\\'
#else
#define PATH_SEPARATOR '/'
#endif
extern "C" {
  int cmd_webpinfo_main(int argc, const char* argv[]);
  int cmd_cwebp_main(int argc, const char* argv[]);
  int cmd_dwebp_main(int argc, const char* argv[]);
}
int main(int argc, const char *argv[]) {
  for (int i = 0; argc != 0 && i != 2; i++) {
    const char *argv0 = strrchr(argv[0], PATH_SEPARATOR);
    if (argv0 == NULL) argv0 = argv[0]; else argv0++;
    if (strcmp(argv0, "webpinfo") == 0) return cmd_webpinfo_main(argc, argv);
    if (strcmp(argv0, "cwebp") == 0) return cmd_cwebp_main(argc, argv);
    if (strcmp(argv0, "dwebp") == 0) return cmd_dwebp_main(argc, argv);
    argv++;
    argc--;
  }
  puts("applets: webpinfo cwebp dwebp");
  return 0;
}

Because libwebp uses cmake and ninja, so here's a util function to extract ninja targets. Then, compile all targets and link them with multicall.cc:

export CFLAGS="-O3 -fomit-frame-pointer -march=x86-64-v3 -flto"
export CXXFLAGS="$CFLAGS"

rm -rf build

# cmake will use CFLAGS/CXXFLAGS from environment
cmake -B build -G Ninja -DCMAKE_BUILD_TYPE=Release -DBUILD_SHARED_LIBS=OFF -DWEBP_USE_THREAD=OFF -DWEBP_UNICODE=OFF

# extract path of targets
ninja_targets(){
  cat build/build.ninja | grep $1 | sed -e 's|\$||g' -e 's/|/ /g' | cut -d " " -f 4- | tr " " "\n" | grep -E "\.[^\\/]+/*{content}*/quot; # get targets built by $1, fix msys2 paths like "D$:/a.o", remove target head and '|' char, exclude targets without extension name
}
webp_targets=""
webp_targets="$webp_targets $(ninja_targets C_EXECUTABLE_LINKER__webpinfo_Release)"
webp_targets="$webp_targets $(ninja_targets C_EXECUTABLE_LINKER__cwebp_Release)"
webp_targets="$webp_targets $(ninja_targets C_EXECUTABLE_LINKER__dwebp_Release)"
ninja -C build $webp_targets

g++ $CXXFLAGS multicall.cc \
  $(realpath $webp_targets) \
  -o zcodecs

Full runnable build script is here (ect + libjxl + libwebp).

As I described here, we can also use objcopy or modify the LLVM IR to rename symbols, however