From 30b21e76792d92d83c5f076079be6ad577e50e5a Mon Sep 17 00:00:00 2001
From: Alex Arslan <ararslan@comcast.net>
Date: Wed, 23 May 2018 08:01:53 -0700
Subject: [PATCH] Add Sys.glibc_version and Sys.isglibc

These functions come in handy when linking to a library that assumes a
particular minimum version of glibc, or for determining whether the
system's libc is musl.

These functions return v0.0.0 and false, respectively, for non-Linux
systems and for Linux systems which do not use glibc.
---
 NEWS.md                                       |  5 +++
 base/sysinfo.jl                               | 39 ++++++++++++++++++-
 doc/src/base/base.md                          |  2 +
 .../handling-operating-system-variation.md    | 13 +++++--
 test/osutils.jl                               |  6 +++
 5 files changed, 61 insertions(+), 4 deletions(-)

diff --git a/NEWS.md b/NEWS.md
index bb198b131ee64..233c184fa5f4c 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -723,6 +723,10 @@ Library improvements
     optional keyword argument, as in `reduce(op, itr; init=v0)`. Similarly for `foldl`,
     `foldr`, `mapreduce`, `mapfoldl` and `mapfoldr`. ([#27711])
 
+  * `Sys.glibc()` determines whether glibc is linked to Julia, and `Sys.glibc_version()`
+    returns the version of the linked glibc if applicable. ([#27223])
+
+
 Compiler/Runtime improvements
 -----------------------------
 
@@ -1640,5 +1644,6 @@ Command-line option changes
 [#27164]: https://github.com/JuliaLang/julia/issues/27164
 [#27189]: https://github.com/JuliaLang/julia/issues/27189
 [#27212]: https://github.com/JuliaLang/julia/issues/27212
+[#27223]: https://github.com/JuliaLang/julia/issues/27223
 [#27248]: https://github.com/JuliaLang/julia/issues/27248
 [#27401]: https://github.com/JuliaLang/julia/issues/27401
diff --git a/base/sysinfo.jl b/base/sysinfo.jl
index ab19d99998bc7..d695ad56c499e 100644
--- a/base/sysinfo.jl
+++ b/base/sysinfo.jl
@@ -26,7 +26,9 @@ export BINDIR,
        isunix,
        iswindows,
        isexecutable,
-       which
+       which,
+       glibc_version,
+       isglibc
 
 import ..Base: show
 
@@ -335,6 +337,41 @@ windows_version
 
 const WINDOWS_VISTA_VER = v"6.0"
 
+if islinux()
+    function glibc_version()
+        # Proxy for a pointer to libc, since libc is linked into Julia
+        libc = ccall(:jl_dlopen, Ptr{Cvoid}, (Ptr{Cvoid}, Cuint), C_NULL, 0x0)
+        @assert libc != C_NULL # We have bigger problems if this is not the case
+        vers_ptr = ccall(:jl_dlsym_e, Ptr{Cvoid}, (Ptr{Cvoid}, Cstring),
+                         libc, "gnu_get_libc_version")
+        vers_ptr == C_NULL && return v"0.0.0" # non-glibc
+        vers_str = unsafe_string(ccall(vers_ptr, Ptr{UInt8}, ()))
+        occursin(Base.VERSION_REGEX, vers_str) ? VersionNumber(vers_str) : v"0.0.0"
+    end
+
+    isglibc() = glibc_version() > v"0.0.0"
+else
+    glibc_version() = v"0.0.0"
+    isglibc() = false
+end
+
+"""
+    Sys.glibc_version()
+
+Return the version of glibc linked to Julia on Linux. This is `v"0.0.0"` on
+other systems as well as Linux systems which use a libc other than glibc
+(e.g. musl).
+"""
+glibc_version
+
+"""
+    Sys.isglibc()
+
+Determine whether Julia links to glibc on the current system. This is `false`
+on systems other than Linux as well as for Linux systems which do not use glibc.
+"""
+isglibc
+
 """
     Sys.isexecutable(path::String)
 
diff --git a/doc/src/base/base.md b/doc/src/base/base.md
index cea99f480b94d..0fe071979de01 100644
--- a/doc/src/base/base.md
+++ b/doc/src/base/base.md
@@ -266,6 +266,8 @@ Base.Sys.islinux
 Base.Sys.isbsd
 Base.Sys.iswindows
 Base.Sys.windows_version
+Base.Sys.glibc_version
+Base.Sys.isglibc
 Base.@static
 ```
 
diff --git a/doc/src/manual/handling-operating-system-variation.md b/doc/src/manual/handling-operating-system-variation.md
index 46ee1ae3a6f70..3ecfd194eb45a 100644
--- a/doc/src/manual/handling-operating-system-variation.md
+++ b/doc/src/manual/handling-operating-system-variation.md
@@ -11,9 +11,16 @@ if Sys.iswindows()
 end
 ```
 
-Note that `islinux` and `isapple` are mutually exclusive subsets of `isunix`. Additionally,
-there is a macro `@static` which makes it possible to use these functions to conditionally hide
-invalid code, as demonstrated in the following examples.
+Note that `islinux` and `isapple` are mutually exclusive subsets of `isunix`.
+
+The `Sys` module also provides functionality for determining the version of glibc, the GNU
+C library, on Linux. This is useful for code that relies on a particular version of glibc.
+Further, the function `isglibc` reports whether glibc is linked to Julia, which can be
+helpful for situations such as determining whether the current system is Alpine Linux, which
+uses musl rather than glibc.
+
+Additionally, there is a macro `@static` which makes it possible to use these functions to
+conditionally hide invalid code, as demonstrated in the following examples.
 
 Simple blocks:
 
diff --git a/test/osutils.jl b/test/osutils.jl
index 2b9da7a3e67bc..db4435f710691 100644
--- a/test/osutils.jl
+++ b/test/osutils.jl
@@ -18,6 +18,12 @@
     else
         @test Sys.windows_version() >= v"1.0.0-"
     end
+    if !Sys.islinux()
+        @test Sys.glibc_version() == v"0.0.0"
+        @test !Sys.isglibc()
+    else
+        @test Sys.glibc_version() >= v"0.0.0"
+    end
 end
 
 @testset "@static" begin