add --trim option for generating smaller binaries (#55047)

This adds a command line option `--trim` that builds images where code
is only included if it is statically reachable from methods marked using
the new function `entrypoint`. Compile-time errors are given for call
sites that are too dynamic to allow trimming the call graph (however
there is an `unsafe` option if you want to try building anyway to see
what happens).

The PR has two other components. One is changes to Base that generally
allow more code to be compiled in this mode. These changes will either
be merged in separate PRs or moved to a separate part of the workflow
(where we will build a custom system image for this purpose). The branch
is set up this way to make it easy to check out and try the
functionality.

The other component is everything in the `juliac/` directory, which
implements a compiler driver script based on this new option, along with
some examples and tests. This will eventually become a package "app"
that depends on PackageCompiler and provides a CLI for all of this
stuff, so it will not be merged here. To try an example:

```
julia contrib/juliac.jl --output-exe hello --trim test/trimming/hello.jl
```

When stripped the resulting executable is currently about 900kb on my
machine.

Also includes a lot of work by @topolarity

---------

Co-authored-by: Gabriel Baraldi <[email protected]>
Co-authored-by: Tim Holy <[email protected]>
Co-authored-by: Cody Tapscott <[email protected]>

Makefile

@@ -82,7 +82,7 @@ julia-deps: | $(DIRS) $(build_datarootdir)/julia/base $(build_datarootdir)/julia
 julia-stdlib: | $(DIRS) julia-deps
 	@$(MAKE) $(QUIET_MAKE) -C $(BUILDROOT)/stdlib
 
-julia-base: julia-deps $(build_sysconfdir)/julia/startup.jl $(build_man1dir)/julia.1 $(build_datarootdir)/julia/julia-config.jl
+julia-base: julia-deps $(build_sysconfdir)/julia/startup.jl $(build_man1dir)/julia.1 $(build_datarootdir)/julia/julia-config.jl $(build_datarootdir)/julia/juliac.jl $(build_datarootdir)/julia/juliac-buildscript.jl
 	@$(MAKE) $(QUIET_MAKE) -C $(BUILDROOT)/base
 
 julia-libccalltest: julia-deps
@@ -181,7 +181,7 @@ $(build_sysconfdir)/julia/startup.jl: $(JULIAHOME)/etc/startup.jl | $(build_sysc
 	@echo Creating usr/etc/julia/startup.jl
 	@cp $< $@
 
-$(build_datarootdir)/julia/julia-config.jl: $(JULIAHOME)/contrib/julia-config.jl | $(build_datarootdir)/julia
+$(build_datarootdir)/julia/%: $(JULIAHOME)/contrib/% | $(build_datarootdir)/julia
 	$(INSTALL_M) $< $(dir $@)
 
 $(build_depsbindir)/stringreplace: $(JULIAHOME)/contrib/stringreplace.c | $(build_depsbindir)

NEWS.md

@@ -4,6 +4,8 @@ Julia v1.12 Release Notes
 New language features
 ---------------------
 
+- New option `--trim` for building "trimmed" binaries, where code not provably reachable from entry points
+  is removed. Entry points can be marked using `Base.Experimental.entrypoint` ([#55047]).
 - A new keyword argument `usings::Bool` has been added to `names`. By using this, we can now
   find all the names available in module `A` by `names(A; all=true, imported=true, usings=true)`. ([#54609])
 - the `@atomic(...)` macro family supports now the reference assignment syntax, e.g.

base/experimental.jl

@@ -457,4 +457,18 @@ without adding them to the global method table.
 """
 :@MethodTable
 
+"""
+    Base.Experimental.entrypoint(f, argtypes::Tuple)
+
+Mark a method for inclusion when the `--trim` option is specified.
+"""
+function entrypoint(@nospecialize(f), @nospecialize(argtypes::Tuple))
+    entrypoint(Tuple{Core.Typeof(f), argtypes...})
+end
+
+function entrypoint(@nospecialize(argt::Type))
+    ccall(:jl_add_entrypoint, Int32, (Any,), argt)
+    nothing
+end
+
 end

base/libuv.jl

@@ -133,7 +133,10 @@ function uv_return_spawn end
 function uv_asynccb end
 function uv_timercb end
 
-function reinit_stdio()
+reinit_stdio() = _reinit_stdio()
+# we need this so it can be called by codegen to print errors, even after
+# reinit_stdio has been redefined by the juliac build script.
+function _reinit_stdio()
     global stdin = init_stdio(ccall(:jl_stdin_stream, Ptr{Cvoid}, ()))::IO
     global stdout = init_stdio(ccall(:jl_stdout_stream, Ptr{Cvoid}, ()))::IO
     global stderr = init_stdio(ccall(:jl_stderr_stream, Ptr{Cvoid}, ()))::IO

base/options.jl

@@ -58,6 +58,7 @@ struct JLOptions
     permalloc_pkgimg::Int8
     heap_size_hint::UInt64
     trace_compile_timing::Int8
+    trim::Int8
 end
 
 # This runs early in the sysimage != is not defined yet

base/reflection.jl

@@ -1504,6 +1504,13 @@ struct CodegenParams
     """
     use_jlplt::Cint
 
+    """
+    If enabled, only provably reachable code (from functions marked with `entrypoint`) is included
+    in the output system image. Errors or warnings can be given for call sites too dynamic to handle.
+    The option is disabled by default. (0=>disabled, 1=>safe (static errors), 2=>unsafe, 3=>unsafe plus warnings)
+    """
+    trim::Cint
+
     """
     A pointer of type
 
@@ -1519,14 +1526,14 @@ struct CodegenParams
                    prefer_specsig::Bool=false,
                    gnu_pubnames::Bool=true, debug_info_kind::Cint = default_debug_info_kind(),
                    debug_info_level::Cint = Cint(JLOptions().debug_level), safepoint_on_entry::Bool=true,
-                   gcstack_arg::Bool=true, use_jlplt::Bool=true,
+                   gcstack_arg::Bool=true, use_jlplt::Bool=true, trim::Cint=Cint(0),
                    lookup::Ptr{Cvoid}=unsafe_load(cglobal(:jl_rettype_inferred_addr, Ptr{Cvoid})))
         return new(
             Cint(track_allocations), Cint(code_coverage),
             Cint(prefer_specsig),
             Cint(gnu_pubnames), debug_info_kind,
             debug_info_level, Cint(safepoint_on_entry),
-            Cint(gcstack_arg), Cint(use_jlplt),
+            Cint(gcstack_arg), Cint(use_jlplt), Cint(trim),
             lookup)
     end
 end

base/strings/io.jl

@@ -51,6 +51,8 @@ function print(io::IO, xs...)
     return nothing
 end
 
+setfield!(typeof(print).name.mt, :max_args, 10, :monotonic)
+
 """
     println([io::IO], xs...)
 
@@ -74,6 +76,7 @@ julia> String(take!(io))
 """
 println(io::IO, xs...) = print(io, xs..., "\n")
 
+setfield!(typeof(println).name.mt, :max_args, 10, :monotonic)
 ## conversion of general objects to strings ##
 
 """
@@ -149,6 +152,7 @@ function print_to_string(xs...)
     end
     String(_unsafe_take!(s))
 end
+setfield!(typeof(print_to_string).name.mt, :max_args, 10, :monotonic)
 
 function string_with_env(env, xs...)
     if isempty(xs)

contrib/julia-config.jl

@@ -67,7 +67,7 @@ function ldlibs(doframework)
         "julia"
     end
     if Sys.isunix()
-        return "-Wl,-rpath,$(shell_escape(libDir())) -Wl,-rpath,$(shell_escape(private_libDir())) -l$libname"
+        return "-L$(shell_escape(private_libDir())) -Wl,-rpath,$(shell_escape(libDir())) -Wl,-rpath,$(shell_escape(private_libDir())) -l$libname"
     else
         return "-l$libname -lopenlibm"
     end