From 269caa8ae18eb33e1286e4c21d434ea07228a619 Mon Sep 17 00:00:00 2001 From: johannst Date: Wed, 10 Apr 2024 19:37:02 +0000 Subject: deploy: ae498864bb638e597b589c52ff27237835625281 --- development/c++.html | 106 ++++++++++++++++++++++++++++++++++++- development/c++/Makefile | 5 +- development/c++/concepts-20.cc | 105 ++++++++++++++++++++++++++++++++++++ development/ld.so.html | 3 ++ development/ldso/samename/Makefile | 13 +++++ development/ldso/samename/lib.c | 9 ++++ development/ldso/samename/main.c | 36 +++++++++++++ 7 files changed, 275 insertions(+), 2 deletions(-) create mode 100644 development/c++/concepts-20.cc create mode 100644 development/ldso/samename/Makefile create mode 100644 development/ldso/samename/lib.c create mode 100644 development/ldso/samename/main.c (limited to 'development') 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");

A more detailed description is available in the SO discussion How does void_t work.

+

Example: Concepts since c++20

+
// 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>; });
+

Template selection with partially / fully specializations.

enum Kind {
     kPrimary,
@@ -886,7 +990,7 @@ int main() {
     // * No specialization matches, take the primary template.
 }
-

Example: Perfect forwarding

+

Example: Perfect forwarding

#include <cassert>
 #include <cstdio>
 #include <new>
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 
+#include 
+
+// 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
+using Alias = T;
+
+void print(int);
+
+// -- CONCEPTS & REQUIRE EXPRESSIONS -------------------------------------------
+
+// Simple concept from a type trait.
+template
+concept Same = std::is_same::value;
+
+// Simple requirement concepts.
+template
+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
+concept TraitTypes = requires(T t) {
+    // T must have a type definition inner.
+    typename T::inner;
+    // Type alias must exist.
+    typename Alias;
+};
+
+// Compound requirement concepts.
+template
+concept TraitFns = requires(T t, const T c) {
+    // void T::foo() must exist.
+    { t.foo() };
+    // bool T::bar() const; must exist.
+    { c.bar() } -> Same;
+    // static void T::stat(); must exist.
+    { T::stat() } -> Same;
+};
+
+// Nested requirement concepts.
+template
+concept TraitNested = requires(T t) {
+    // Must satisfy other concepts.
+    requires TraitTypes;
+    requires TraitFns;
+};
+
+// -- REQUIRE EXPRESSIONS ------------------------------------------------------
+
+// Require expressions can be evaluated to booleans.
+template
+static constexpr bool IsTraitFns = requires { requires TraitFns; };
+
+// Require expressions can also be used in static assertions.
+static_assert(requires { requires Same; });
+static_assert(!requires {
+    typename Alias;
+    requires Same;
+});
+
+// -- TESTS --------------------------------------------------------------------
+
+static_assert(requires { requires TraitAddAndPrint; });
+
+struct FnTypeGood {
+    using inner = int;
+};
+struct FnTypeBad {};
+static_assert(requires { requires TraitTypes; });
+static_assert(!requires { requires TraitTypes; });
+
+struct FnGood {
+    void foo();
+    bool bar() const;
+    static int stat();
+};
+struct FnBad {};
+static_assert(requires { requires TraitFns; });
+static_assert(!requires { requires TraitFns; });
+
+struct NestedGood : FnTypeGood, FnGood {};
+struct NestedBad1 : FnGood {};
+struct NestedBad2 : FnTypeGood {};
+static_assert(requires { requires TraitNested; });
+static_assert(!requires { requires TraitNested; });
+static_assert(!requires { requires TraitNested; });
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)
+

Load lib with same name from different locations

+

The sources in ldso/samename show some experiments, loading the +libs with the same name but potentially from different locations (paths).

Dynamic Linking (x86_64)

Dynamic linking basically works via one indirect jump. It uses a combination of function trampolines (.plt section) and a function pointer table (.got.plt 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 + +#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 +#include +#include +#include + +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; +} -- cgit v1.2.3