Adding -DCMAKE_C_FLAGS_RELEASE="-static" -DCMAKE_EXE_LINKER_FLAGS="-static" slows down avifenc runtime

[FrankGalligan]

Following this guide calling avifenc is slower than compared to building with this cmake line

cmake -S libavif -B libavif/build -DBUILD_SHARED_LIBS=OFF -DAVIF_CODEC_AOM=LOCAL -DAVIF_LIBYUV=LOCAL -DAVIF_LIBSHARPYUV=LOCAL -DAVIF_JPEG=LOCAL -DAVIF_ZLIBPNG=LOCAL -DAVIF_BUILD_APPS=ON

Steps to reproduce:

1. Download jpeg image from here
2. Build avifenc according to the guide.
3. Build avifenc removing the flags.
4. Run time ./avifenc happy_dog.jpg example.avif
5. Run time ./avifenc_no_flags happy_dog.jpg example.avif

On my machine this was the output from step 4:

Wrote AVIF: example.avif

real	0m2.421s

And output from step 5:

Wrote AVIF: example.avif

real	0m0.738s

[wantehchang]

The -DCMAKE_C_FLAGS_RELEASE="-static" option is problematic. The default value of CMAKE_C_FLAGS_RELEASE depends on the compiler. For GCC and Clang on Linux, CMAKE_C_FLAGS_RELEASE is -O3 -DNDEBUG. Replacing it with -static means compiler optimizations are disabled and assertions are left enabled.

Frank, could you try changing -DCMAKE_C_FLAGS_RELEASE="-static" to -DCMAKE_C_FLAGS_RELEASE="-static -O3 -DNDEBUG"?

[FrankGalligan]

That fixed the performance issue.

[wantehchang]

Yannis: You added -DCMAKE_C_FLAGS_RELEASE="-static" -DCMAKE_EXE_LINKER_FLAGS="-static" in e9db3c3f1. Do you remember why? Is it because we are not passing -DBUILD_SHARED_LIBS=OFF to the external dependencies built by cmake's FetchContent method?

If it is necessary to use the -static linker flag, we can set the following three environment variables before the first cmake command in https://github.com/AOMediaCodec/libavif?tab=readme-ov-file#build-everything-from-scratch:

export CFLAGS=-static
export CXXFLAGS=-static
export LDFLAGS=-static

But it doesn't seem useful to generate fully static binaries. If I don't use the -static linker flag, the avifenc binary I built only depends on the system libraries:

$ ldd libavif/build/avifenc
	linux-vdso.so.1 (0x00007fb6a01bb000)
	libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007fb6a00b4000)
	libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007fb69f417000)
	/lib64/ld-linux-x86-64.so.2 (0x00007fb6a01bd000)

[y-guyon]

Yannis: You added -DCMAKE_C_FLAGS_RELEASE="-static" -DCMAKE_EXE_LINKER_FLAGS="-static" in e9db3c3f1. Do you remember why?

The previous line states

libavif/README.md

Line 158 in bdba09d

For development and debugging purposes, or to generate fully static binaries:

so it makes sense to remove compiler optimizations and to make sure it is fully static.
Fully static can be useful when generating binaries that run on distributed frameworks.

Is it because we are not passing -DBUILD_SHARED_LIBS=OFF to the external dependencies built by cmake's FetchContent method?

Maybe that but probably not only.

If I don't use the -static linker flag, the avifenc binary I built only depends on the system libraries

So it is not "fully static" then?

[wantehchang]

Thanks for the reply. I understand it now.

For debugging purposes, it is also helpful to include symbolic information for the debugger (e.g., the -g compiler option). So the current command line is also problematic.

We can consider splitting "For development and debugging purposes" and "to generate fully static binaries":

• For development and debugging purposes: pass -DCMAKE_BUILD_TYPE=Debug (include symbolic debug info, enable assertions, disable compiler optimizations), or -DCMAKE_BUILD_TYPE=RelWithDebInfo (include symbolic debug info, disable assertions, enable compiler optimizations).
• To generate fully static binaries: set the CFLAGS, CXXFLAGS, and LDFLAGS environment variables to -static before running the cmake configure command.

[y-guyon]

We can consider splitting "For development and debugging purposes" and "to generate fully static binaries"

Done in #2642.