deploy: ae498864bb638e597b589c52ff27237835625281

7 files changed, 275 insertions, 2 deletions

diff --git a/development/c++.html b/development/c++.html
index 0d95860..a868300 100644
--- a/development/c++.html
+++ b/development/c++.html
@@ -813,6 +813,110 @@ static_assert(!is_valid<B>::value, "is false");
 </blockquote>
 <p>A more detailed description is available in the SO discussion <a href="https://stackoverflow.com/a/27688405">How does
 <code>void_t</code> work</a>.</p>
+<h2 id="example-concepts-since-c20"><a class="header" href="#example-concepts-since-c20">Example: Concepts since c++20</a></h2>
+<pre><code class="language-cpp">// REQUIRES EXPRESSION
+//   requires { requirement-seq }
+//   requires ( parameter-list ) { requirement-seq }
+//
+// [1] https://en.cppreference.com/w/cpp/language/requires
+// [2] https://en.cppreference.com/w/cpp/language/constraints#Constraints
+//
+// REQUIREMENT CLAUSE
+//   Not the same as a REQUIREMENT EXPRESSIONS, and is used to require
+//   constraints (express concept bounds).
+//
+// [1] https://en.cppreference.com/w/cpp/language/constraints#Requires_clauses
+
+// -- HELPER -------------------------------------------------------------------
+
+template&lt;typename T&gt;
+using Alias = T;
+
+void print(int);
+
+// -- CONCEPTS &amp; REQUIRE EXPRESSIONS -------------------------------------------
+
+// Simple concept from a type trait.
+template&lt;typename T, typename U&gt;
+concept Same = std::is_same&lt;T, U&gt;::value;
+
+// Simple requirement concepts.
+template&lt;typename T&gt;
+concept TraitAddAndPrint = requires(T t, int i) {
+    // Adding T + int must be supported.
+    t + i;
+    // Calling print(T) must be available.
+    print(t);
+};
+
+// Type requirement concepts.
+template&lt;typename T&gt;
+concept TraitTypes = requires(T t) {
+    // T must have a type definition inner.
+    typename T::inner;
+    // Type alias must exist.
+    typename Alias&lt;T&gt;;
+};
+
+// Compound requirement concepts.
+template&lt;typename T&gt;
+concept TraitFns = requires(T t, const T c) {
+    // void T::foo() must exist.
+    { t.foo() };
+    // bool T::bar() const; must exist.
+    { c.bar() } -&gt; Same&lt;bool&gt;;
+    // static void T::stat(); must exist.
+    { T::stat() } -&gt; Same&lt;int&gt;;
+};
+
+// Nested requirement concepts.
+template&lt;typename T&gt;
+concept TraitNested = requires(T t) {
+    // Must satisfy other concepts.
+    requires TraitTypes&lt;T&gt;;
+    requires TraitFns&lt;T&gt;;
+};
+
+// -- REQUIRE EXPRESSIONS ------------------------------------------------------
+
+// Require expressions can be evaluated to booleans.
+template&lt;typename T&gt;
+static constexpr bool IsTraitFns = requires { requires TraitFns&lt;T&gt;; };
+
+// Require expressions can also be used in static assertions.
+static_assert(requires { requires Same&lt;int, int&gt;; });
+static_assert(!requires {
+    typename Alias&lt;int&gt;;
+    requires Same&lt;int, void&gt;;
+});
+
+// -- TESTS --------------------------------------------------------------------
+
+static_assert(requires { requires TraitAddAndPrint&lt;int&gt;; });
+
+struct FnTypeGood {
+    using inner = int;
+};
+struct FnTypeBad {};
+static_assert(requires { requires TraitTypes&lt;FnTypeGood&gt;; });
+static_assert(!requires { requires TraitTypes&lt;FnTypeBad&gt;; });
+
+struct FnGood {
+    void foo();
+    bool bar() const;
+    static int stat();
+};
+struct FnBad {};
+static_assert(requires { requires TraitFns&lt;FnGood&gt;; });
+static_assert(!requires { requires TraitFns&lt;FnBad&gt;; });
+
+struct NestedGood : FnTypeGood, FnGood {};
+struct NestedBad1 : FnGood {};
+struct NestedBad2 : FnTypeGood {};
+static_assert(requires { requires TraitNested&lt;NestedGood&gt;; });
+static_assert(!requires { requires TraitNested&lt;NestedBad1&gt;; });
+static_assert(!requires { requires TraitNested&lt;NestedBad2&gt;; });
+</code></pre>
 <h2 id="template-selection-with-partially--fully-specializations"><a class="header" href="#template-selection-with-partially--fully-specializations">Template selection with partially / fully specializations.</a></h2>
 <pre><code class="language-cpp">enum Kind {
     kPrimary,
@@ -886,7 +990,7 @@ int main() {
     // * No specialization matches, take the primary template.
 }
 </code></pre>
-<h1 id="example-perfect-forwarding"><a class="header" href="#example-perfect-forwarding">Example: Perfect forwarding</a></h1>
+<h2 id="example-perfect-forwarding"><a class="header" href="#example-perfect-forwarding">Example: Perfect forwarding</a></h2>
 <pre><code class="language-cpp">#include &lt;cassert&gt;
 #include &lt;cstdio&gt;
 #include &lt;new&gt;
diff --git a/development/c++/Makefile b/development/c++/Makefile
index 622bfd3..2c53e47 100644
--- a/development/c++/Makefile
+++ b/development/c++/Makefile
@@ -1,4 +1,4 @@
-SRC = concepts-11.cc meta.cc meta2.cc meta4.cc tmpl-pair.cc tmpl-void_t.cc fwd.cc fwd-perfect.cc
+SRC = concepts-11.cc concepts-20.cc meta.cc meta2.cc meta4.cc tmpl-pair.cc tmpl-void_t.cc fwd.cc fwd-perfect.cc
 BIN = $(SRC:.cc=)
 
 all: $(BIN)
@@ -6,6 +6,9 @@ all: $(BIN)
 %: %.cc
 	$(CXX) -o $* $^ -std=c++17 -g -fsanitize=address -fsanitize=undefined -fsanitize=leak
 
+concepts-20: concepts-20.cc
+	$(CXX) -fsyntax-only $^ -std=c++20
+
 fmt:
 	clang-format -i $(SRC)
 
diff --git a/development/c++/concepts-20.cc b/development/c++/concepts-20.cc
new file mode 100644
index 0000000..018b30b
--- /dev/null
+++ b/development/c++/concepts-20.cc
@@ -0,0 +1,105 @@
+#include <concepts>
+#include <type_traits>
+
+// REQUIRES EXPRESSION
+//   requires { requirement-seq }
+//   requires ( parameter-list ) { requirement-seq }
+//
+// [1] https://en.cppreference.com/w/cpp/language/requires
+// [2] https://en.cppreference.com/w/cpp/language/constraints#Constraints
+//
+// REQUIREMENT CLAUSE
+//   Not the same as a REQUIREMENT EXPRESSIONS, and is used to require
+//   constraints (express concept bounds).
+//
+// [1] https://en.cppreference.com/w/cpp/language/constraints#Requires_clauses
+
+// -- HELPER -------------------------------------------------------------------
+
+template<typename T>
+using Alias = T;
+
+void print(int);
+
+// -- CONCEPTS & REQUIRE EXPRESSIONS -------------------------------------------
+
+// Simple concept from a type trait.
+template<typename T, typename U>
+concept Same = std::is_same<T, U>::value;
+
+// Simple requirement concepts.
+template<typename T>
+concept TraitAddAndPrint = requires(T t, int i) {
+    // Adding T + int must be supported.
+    t + i;
+    // Calling print(T) must be available.
+    print(t);
+};
+
+// Type requirement concepts.
+template<typename T>
+concept TraitTypes = requires(T t) {
+    // T must have a type definition inner.
+    typename T::inner;
+    // Type alias must exist.
+    typename Alias<T>;
+};
+
+// Compound requirement concepts.
+template<typename T>
+concept TraitFns = requires(T t, const T c) {
+    // void T::foo() must exist.
+    { t.foo() };
+    // bool T::bar() const; must exist.
+    { c.bar() } -> Same<bool>;
+    // static void T::stat(); must exist.
+    { T::stat() } -> Same<int>;
+};
+
+// Nested requirement concepts.
+template<typename T>
+concept TraitNested = requires(T t) {
+    // Must satisfy other concepts.
+    requires TraitTypes<T>;
+    requires TraitFns<T>;
+};
+
+// -- REQUIRE EXPRESSIONS ------------------------------------------------------
+
+// Require expressions can be evaluated to booleans.
+template<typename T>
+static constexpr bool IsTraitFns = requires { requires TraitFns<T>; };
+
+// Require expressions can also be used in static assertions.
+static_assert(requires { requires Same<int, int>; });
+static_assert(!requires {
+    typename Alias<int>;
+    requires Same<int, void>;
+});
+
+// -- TESTS --------------------------------------------------------------------
+
+static_assert(requires { requires TraitAddAndPrint<int>; });
+
+struct FnTypeGood {
+    using inner = int;
+};
+struct FnTypeBad {};
+static_assert(requires { requires TraitTypes<FnTypeGood>; });
+static_assert(!requires { requires TraitTypes<FnTypeBad>; });
+
+struct FnGood {
+    void foo();
+    bool bar() const;
+    static int stat();
+};
+struct FnBad {};
+static_assert(requires { requires TraitFns<FnGood>; });
+static_assert(!requires { requires TraitFns<FnBad>; });
+
+struct NestedGood : FnTypeGood, FnGood {};
+struct NestedBad1 : FnGood {};
+struct NestedBad2 : FnTypeGood {};
+static_assert(requires { requires TraitNested<NestedGood>; });
+static_assert(!requires { requires TraitNested<NestedBad1>; });
+static_assert(!requires { requires TraitNested<NestedBad2>; });
diff --git a/development/ld.so.html b/development/ld.so.html
index c0d088b..6c0e2f0 100644
--- a/development/ld.so.html
+++ b/development/ld.so.html
@@ -352,6 +352,9 @@ symbol=default_main;  lookup in file=/usr/lib/libc.so.6 [0]
 symbol=default_main;  lookup in file=/lib64/ld-linux-x86-64.so.2 [0]
 ./main: error: symbol lookup error: undefined symbol: default_main (fatal)
 </code></pre>
+<h2 id="load-lib-with-same-name-from-different-locations"><a class="header" href="#load-lib-with-same-name-from-different-locations">Load lib with same name from different locations</a></h2>
+<p>The sources in <a href="https://github.com/johannst/notes/tree/master/src/development/ldso/samename">ldso/samename</a> show some experiments, loading the
+libs with the same name but potentially from different locations (paths).</p>
 <h2 id="dynamic-linking-x86_64"><a class="header" href="#dynamic-linking-x86_64">Dynamic Linking (x86_64)</a></h2>
 <p>Dynamic linking basically works via one indirect jump. It uses a combination of
 function trampolines (<code>.plt</code> section) and a function pointer table (<code>.got.plt</code>
diff --git a/development/ldso/samename/Makefile b/development/ldso/samename/Makefile
new file mode 100644
index 0000000..f35a1e3
--- /dev/null
+++ b/development/ldso/samename/Makefile
@@ -0,0 +1,13 @@
+all:
+	mkdir -p foo bar
+	gcc -g -o foo/lib.so lib.c -shared -fPIC -DNAME=\"foo\"
+	gcc -g -o bar/lib.so lib.c -shared -fPIC -DNAME=\"bar\"
+	gcc -g -o main main.c -ldl
+	./main foo/lib.so bar/lib.so
+	LD_LIBRARY_PATH=foo:bar ./main lib.so lib.so
+	LD_LIBRARY_PATH=bar:foo ./main lib.so lib.so
+	LD_LIBRARY_PATH=foo ./main lib.so foo/lib.so
+	LD_LIBRARY_PATH=foo ./main lib.so bar/lib.so
+
+clean:
+	$(RM) -r foo bar main
diff --git a/development/ldso/samename/lib.c b/development/ldso/samename/lib.c
new file mode 100644
index 0000000..d467d7f
--- /dev/null
+++ b/development/ldso/samename/lib.c
@@ -0,0 +1,9 @@
+#include <stdio.h>
+
+#ifndef NAME
+#define NAME __FILE_NAME__
+#endif
+
+void moose() {
+  puts(NAME " says moose");
+}
diff --git a/development/ldso/samename/main.c b/development/ldso/samename/main.c
new file mode 100644
index 0000000..6d6a8ea
--- /dev/null
+++ b/development/ldso/samename/main.c
@@ -0,0 +1,36 @@
+#include <assert.h>
+#include <dlfcn.h>
+#include <stdio.h>
+#include <string.h>
+
+void print_libso() {
+  FILE* m = fopen("/proc/self/maps", "r");
+  assert(m);
+
+  char line[256];
+  while (fgets(line, sizeof(line), m)) {
+    if (strstr(line, "lib.so")) {
+      printf("%s", line);
+    }
+  }
+  fclose(m);
+}
+
+int main(int argc, char* argv[]) {
+  for (int i = 1; i < argc; ++i) {
+    void* h = dlopen(argv[i], RTLD_LAZY | RTLD_GLOBAL);
+    if (!h) {
+      puts(dlerror());
+      return 1;
+    }
+
+    void (*next)() = dlsym(h, "moose");
+    assert(next);
+    next();
+
+    // leak lib, we want to priint the mmap.
+  }
+
+  print_libso();
+  return 0;
+}