Move Libdl into Base

We need to `dlopen()` things in Base a lot more due to using JLL
packages within `Base` and the standard library.  We move `Libdl` into
`Base.Libc`, but continue to carry a shell `Libdl` stdlib that
re-exports all relevant pieces of functionality, for
backwards-compatibility.

NEWS.md

@@ -57,6 +57,7 @@ Standard library changes
 * `sum`, `prod`, `maximum`, and `minimum` now support `init` keyword argument ([#36188], [#35839]).
 * `unique(f, itr; seen=Set{T}())` now allows you to declare the container type used for
   keeping track of values returned by `f` on elements of `itr` ([#36280]).
+* `Libdl` has been moved to `Base.Libc.Libdl`, however it is still accessible as an stdlib ([#35628]).
 
 #### LinearAlgebra
 * New method `LinearAlgebra.issuccess(::CholeskyPivoted)` for checking whether pivoted Cholesky factorization was successful ([#36002]).

base/Base.jl

@@ -165,6 +165,20 @@ include("strings/substring.jl")
 include(string((length(Core.ARGS)>=2 ? Core.ARGS[2] : ""), "build_h.jl"))     # include($BUILDROOT/base/build_h.jl)
 include(string((length(Core.ARGS)>=2 ? Core.ARGS[2] : ""), "version_git.jl")) # include($BUILDROOT/base/version_git.jl)
 
+# Initialize DL_LOAD_PATH as early as possible.  We are defining things here in
+# a slightly more verbose fashion than usual, because we're running so early.
+const DL_LOAD_PATH = String[]
+let os = ccall(:jl_get_UNAME, Any, ())
+    if os === :Darwin || os === :Apple
+        if Base.DARWIN_FRAMEWORK
+            push!(DL_LOAD_PATH, "@loader_path/Frameworks")
+        else
+            push!(DL_LOAD_PATH, "@loader_path/julia")
+        end
+        push!(DL_LOAD_PATH, "@loader_path")
+    end
+end
+
 include("osutils.jl")
 include("c.jl")
 
@@ -204,16 +218,6 @@ include("sysinfo.jl")
 include("libc.jl")
 using .Libc: getpid, gethostname, time
 
-const DL_LOAD_PATH = String[]
-if Sys.isapple()
-    if Base.DARWIN_FRAMEWORK
-        push!(DL_LOAD_PATH, "@loader_path/Frameworks")
-    else
-        push!(DL_LOAD_PATH, "@loader_path/julia")
-    end
-    push!(DL_LOAD_PATH, "@loader_path")
-end
-
 include("env.jl")
 
 # Concurrency

base/libc.jl

@@ -402,4 +402,8 @@ Interface to the C `srand(seed)` function.
 """
 srand(seed=floor(Int, time()) % Cuint) = ccall(:srand, Cvoid, (Cuint,), seed)
 
+# Include dlopen()/dlpath() code
+include("libdl.jl")
+using .Libdl
+
 end # module

base/libdl.jl

@@ -0,0 +1,314 @@
+# This file is a part of Julia. License is MIT: https://julialang.org/license
+
+module Libdl
+@doc """
+Interface to libdl. Provides dynamic linking support.
+""" Libdl
+
+import Base.DL_LOAD_PATH
+
+export DL_LOAD_PATH, RTLD_DEEPBIND, RTLD_FIRST, RTLD_GLOBAL, RTLD_LAZY, RTLD_LOCAL,
+    RTLD_NODELETE, RTLD_NOLOAD, RTLD_NOW, dlclose, dlopen, dlopen_e, dlsym, dlsym_e,
+    dlpath, find_library, dlext, dllist
+
+"""
+    DL_LOAD_PATH
+
+When calling [`dlopen`](@ref), the paths in this list will be searched first, in
+order, before searching the system locations for a valid library handle.
+"""
+DL_LOAD_PATH
+
+# note: constants to match JL_RTLD_* in src/julia.h, translated
+#       to system-specific values by JL_RTLD macro in src/dlload.c
+const RTLD_LOCAL     = 0x00000001
+const RTLD_GLOBAL    = 0x00000002
+const RTLD_LAZY      = 0x00000004
+const RTLD_NOW       = 0x00000008
+const RTLD_NODELETE  = 0x00000010
+const RTLD_NOLOAD    = 0x00000020
+const RTLD_DEEPBIND  = 0x00000040
+const RTLD_FIRST     = 0x00000080
+
+"""
+    RTLD_DEEPBIND
+    RTLD_FIRST
+    RTLD_GLOBAL
+    RTLD_LAZY
+    RTLD_LOCAL
+    RTLD_NODELETE
+    RTLD_NOLOAD
+    RTLD_NOW
+
+Enum constant for [`dlopen`](@ref). See your platform man page for details, if
+applicable.
+"""
+(RTLD_DEEPBIND, RTLD_FIRST, RTLD_GLOBAL, RTLD_LAZY, RTLD_LOCAL, RTLD_NODELETE, RTLD_NOLOAD, RTLD_NOW)
+
+"""
+    dlsym(handle, sym)
+
+Look up a symbol from a shared library handle, return callable function pointer on success.
+"""
+function dlsym(hnd::Ptr, s::Union{Symbol,AbstractString}; throw_error::Bool = true)
+    hnd == C_NULL && throw(ArgumentError("NULL library handle"))
+    val = Ref(Ptr{Cvoid}(0))
+    symbol_found = ccall(:jl_dlsym, Cint,
+        (Ptr{Cvoid}, Cstring, Ref{Ptr{Cvoid}}, Cint),
+        hnd, s, val, Int64(throw_error)
+    )
+    if symbol_found == 0
+        return nothing
+    end
+    return val[]
+end
+
+"""
+    dlsym_e(handle, sym)
+
+Look up a symbol from a shared library handle, silently return `C_NULL` on lookup failure.
+This method is now deprecated in favor of `dlsym(handle, sym; throw_error=false)`.
+"""
+function dlsym_e(hnd::Ptr, s::Union{Symbol,AbstractString})
+    return something(dlsym(hnd, s; throw_error=false), C_NULL)
+end
+
+"""
+    dlopen(libfile::AbstractString [, flags::Integer]; throw_error:Bool = true)
+
+Load a shared library, returning an opaque handle.
+
+The extension given by the constant `dlext` (`.so`, `.dll`, or `.dylib`)
+can be omitted from the `libfile` string, as it is automatically appended
+if needed.   If `libfile` is not an absolute path name, then the paths
+in the array `DL_LOAD_PATH` are searched for `libfile`, followed by the
+system load path.
+
+The optional flags argument is a bitwise-or of zero or more of `RTLD_LOCAL`, `RTLD_GLOBAL`,
+`RTLD_LAZY`, `RTLD_NOW`, `RTLD_NODELETE`, `RTLD_NOLOAD`, `RTLD_DEEPBIND`, and `RTLD_FIRST`.
+These are converted to the corresponding flags of the POSIX (and/or GNU libc and/or MacOS)
+dlopen command, if possible, or are ignored if the specified functionality is not available
+on the current platform. The default flags are platform specific. On MacOS the default
+`dlopen` flags are `RTLD_LAZY|RTLD_DEEPBIND|RTLD_GLOBAL` while on other platforms the
+defaults are `RTLD_LAZY|RTLD_DEEPBIND|RTLD_LOCAL`. An important usage of these flags is to
+specify non default behavior for when the dynamic library loader binds library references to
+exported symbols and if the bound references are put into process local or global scope. For
+instance `RTLD_LAZY|RTLD_DEEPBIND|RTLD_GLOBAL` allows the library's symbols to be available
+for usage in other shared libraries, addressing situations where there are dependencies
+between shared libraries.
+
+If the library cannot be found, this method throws an error, unless the keyword argument
+`throw_error` is set to `false`, in which case this method returns `nothing`.
+
+!!! note
+     From Julia 1.6 on, this method replaces paths starting with `@executable_path/` with
+     the path to the Julia executable, allowing for relocatable relative-path loads. In
+     Julia 1.5 and earlier, this only worked on macOS.
+"""
+function dlopen end
+
+dlopen(s::Symbol, flags::Integer = RTLD_LAZY | RTLD_DEEPBIND; kwargs...) =
+    dlopen(string(s), flags; kwargs...)
+
+function dlopen(s::AbstractString, flags::Integer = RTLD_LAZY | RTLD_DEEPBIND; throw_error::Bool = true)
+    ret = ccall(:jl_load_dynamic_library, Ptr{Cvoid}, (Cstring,UInt32,Cint), s, flags, Cint(throw_error))
+    if ret == C_NULL
+        return nothing
+    end
+    return ret
+end
+
+"""
+    dlopen(f::Function, args...; kwargs...)
+
+Wrapper for usage with `do` blocks to automatically close the dynamic library once
+control flow leaves the `do` block scope.
+
+# Example
+```julia
+vendor = dlopen("libblas") do lib
+    if Libdl.dlsym(lib, :openblas_set_num_threads; throw_error=false) !== nothing
+        return :openblas
+    else
+        return :other
+    end
+end
+```
+"""
+function dlopen(f::Function, args...; kwargs...)
+    hdl = nothing
+    try
+        hdl = dlopen(args...; kwargs...)
+        f(hdl)
+    finally
+        dlclose(hdl)
+    end
+end
+
+"""
+    dlopen_e(libfile::AbstractString [, flags::Integer])
+
+Similar to [`dlopen`](@ref), except returns `C_NULL` instead of raising errors.
+This method is now deprecated in favor of `dlopen(libfile::AbstractString [, flags::Integer]; throw_error=false)`.
+"""
+dlopen_e(args...) = something(dlopen(args...; throw_error=false), C_NULL)
+
+"""
+    dlclose(handle)
+
+Close shared library referenced by handle.
+"""
+function dlclose(p::Ptr)
+    0 == ccall(:jl_dlclose, Cint, (Ptr{Cvoid},), p)
+end
+
+"""
+    dlclose(::Nothing)
+
+For the very common pattern usage pattern of
+
+    try
+        hdl = dlopen(library_name)
+        ... do something
+    finally
+        dlclose(hdl)
+    end
+
+We define a `dlclose()` method that accepts a parameter of type `Nothing`, so
+that user code does not have to change its behavior for the case that `library_name`
+was not found.
+"""
+function dlclose(p::Nothing)
+end
+
+"""
+    find_library(names, locations)
+
+Searches for the first library in `names` in the paths in the `locations` list,
+`DL_LOAD_PATH`, or system library paths (in that order) which can successfully be dlopen'd.
+On success, the return value will be one of the names (potentially prefixed by one of the
+paths in locations). This string can be assigned to a `global const` and used as the library
+name in future `ccall`'s. On failure, it returns the empty string.
+"""
+function find_library(libnames, extrapaths=String[])
+    for lib in libnames
+        for path in extrapaths
+            l = joinpath(path, lib)
+            p = dlopen(l, RTLD_LAZY; throw_error=false)
+            if p !== nothing
+                dlclose(p)
+                return l
+            end
+        end
+        p = dlopen(lib, RTLD_LAZY; throw_error=false)
+        if p !== nothing
+            dlclose(p)
+            return lib
+        end
+    end
+    return ""
+end
+find_library(libname::Union{Symbol,AbstractString}, extrapaths=String[]) =
+    find_library([string(libname)], extrapaths)
+
+"""
+    dlpath(handle::Ptr{Cvoid})
+
+Given a library `handle` from `dlopen`, return the full path.
+"""
+function dlpath(handle::Ptr{Cvoid})
+    p = ccall(:jl_pathname_for_handle, Cstring, (Ptr{Cvoid},), handle)
+    s = unsafe_string(p)
+    Sys.iswindows() && Libc.free(p)
+    return s
+end
+
+"""
+    dlpath(libname::Union{AbstractString, Symbol})
+
+Get the full path of the library `libname`.
+
+# Example
+```julia-repl
+julia> dlpath("libjulia")
+```
+"""
+function dlpath(libname::Union{AbstractString, Symbol})
+    handle = dlopen(libname)
+    path = dlpath(handle)
+    dlclose(handle)
+    return path
+end
+
+if Sys.isapple()
+    const dlext = "dylib"
+elseif Sys.iswindows()
+    const dlext = "dll"
+else
+    #assume Sys.islinux, or similar
+    const dlext = "so"
+end
+
+"""
+    dlext
+
+File extension for dynamic libraries (e.g. dll, dylib, so) on the current platform.
+"""
+dlext
+
+if (Sys.islinux() || Sys.isbsd()) && !Sys.isapple()
+    struct dl_phdr_info
+        # Base address of object
+        addr::Cuint
+
+        # Null-terminated name of object
+        name::Ptr{UInt8}
+
+        # Pointer to array of ELF program headers for this object
+        phdr::Ptr{Cvoid}
+
+        # Number of program headers for this object
+        phnum::Cshort
+    end
+
+    # This callback function called by dl_iterate_phdr() on Linux and BSD's
+    # DL_ITERATE_PHDR(3) on freebsd
+    function dl_phdr_info_callback(di::dl_phdr_info, size::Csize_t, dynamic_libraries::Array{String,1})
+        name = unsafe_string(di.name)
+        push!(dynamic_libraries, name)
+        return Cint(0)
+    end
+end
+
+"""
+    dllist()
+
+Return the paths of dynamic libraries currently loaded in a `Vector{String}`.
+"""
+function dllist()
+    dynamic_libraries = Vector{String}()
+
+    @static if Sys.isapple()
+        numImages = ccall(:_dyld_image_count, Cint, ())
+
+        # start at 1 instead of 0 to skip self
+        for i in 1:numImages-1
+            name = unsafe_string(ccall(:_dyld_get_image_name, Cstring, (UInt32,), i))
+            push!(dynamic_libraries, name)
+        end
+    elseif Sys.islinux() || Sys.isbsd()
+        callback = @cfunction(dl_phdr_info_callback, Cint,
+                              (Ref{dl_phdr_info}, Csize_t, Ref{Vector{String}}))
+        ccall(:dl_iterate_phdr, Cint, (Ptr{Cvoid}, Ref{Vector{String}}), callback, dynamic_libraries)
+        popfirst!(dynamic_libraries)
+        filter!(!isempty, dynamic_libraries)
+    elseif Sys.iswindows()
+        ccall(:jl_dllist, Cint, (Any,), dynamic_libraries)
+    else
+        # unimplemented
+    end
+
+    return dynamic_libraries
+end
+
+end # module Libdl