P0012R1, accepted into C++17, makes a function’s “noexcept” (or
“throw()”) specification part of its signature. GCC 7.2 provides a
warning, -Wnoexcept-type, that is triggered when a function pointer type
with an exception specification is used in pre-C++17 code in such a way
as to pose an ABI incompatibility with C++17 code.
https://gcc.gnu.org/onlinedocs/gcc-7.2.0/gcc/C_002b_002b-Dialect-Options.html#index-Wnoexcept-type
Warnings are of the form:
In file included from ../../util/misc/from_pointer_cast_test.cc:15:0:
../../util/misc/from_pointer_cast.h:64:1: error: mangled name for ‘typename std::enable_if<(std::is_pointer<From>::value && std::is_pointer<_Tp>::value), To>::type crashpad::FromPointerCast(From) [with To = const volatile void*; From = void* (*)(long unsigned int) throw ()]’ will change in C++17 because the exception specification is part of a function type [-Werror=noexcept-type]
FromPointerCast(From from) {
^~~~~~~~~~~~~~~
../../util/misc/from_pointer_cast.h:64:1: error: mangled name for ‘typename std::enable_if<(std::is_pointer<From>::value && std::is_pointer<_Tp>::value), To>::type crashpad::FromPointerCast(From) [with To = volatile void*; From = void* (*)(long unsigned int) throw ()]’ will change in C++17 because the exception specification is part of a function type [-Werror=noexcept-type]
In Crashpad, this warning is triggered by the two FromPointerCast<>()
variants that accept function pointer “From” arguments. This occurs when
using glibc as the standard C library, since glibc declares its
functions as “throw()”. FromPointerCast<>() is used with pointers to
glibc functions such as malloc() and getpid().
The warning is disabled for the FromPointerCast<>() variants that would
trigger it. The warning is not useful or actionable in this internal
Crashpad code where ABI changes due to language version (including
mangling changes) are not a concern.
Clang 4.0 has the similar -Wc++1z-compat-mangling option (also available
as -Wc++17-compat-mangling and the GCC-compatible -Wnoexcept-type in
Clang 5.0) but it is not triggered by this pattern.
Change-Id: Id293db3954be415f67a55476ca72bfb7d399aa3b
Reviewed-on: https://chromium-review.googlesource.com/738292
Reviewed-by: Joshua Peraza <jperaza@chromium.org>
Commit-Queue: Mark Mentovai <mark@chromium.org>
I opted to leave casts to types that were definitely the same size
alone. reinterpret_cast<uintptr_t>(pointer) and
reinterpret_cast<intptr_t>(pointer) should always be safe, for example.
Casts to other integral types have been replaced with
FromPointerCast<>(), which does zero-extension or sign-extension based
on the target type.
To make it possible to use FromPointerCast<>() with some use sites that
were already using checked_cast<>(), FromPointerCast<>() now uses
check_cast<>() when converting to a narrower type.
Test: crashpad_util_test FromPointerCast*, others
Change-Id: I4a71b4aa2d87f545c75524290a702f5f3138d675
Reviewed-on: https://chromium-review.googlesource.com/489701
Reviewed-by: Scott Graham <scottmg@chromium.org>
Some of the new Linux/Android tests were failing in 32-bit code where
pointers were being casted via reinterpret_cast<>() to LinuxVMAddress,
an unsigned 64-bit type. The behavior of such casts is
implementation-defined, and in this case, sign-extension was being used
to convert the 32-bit pointers to 64 bits, resulting in very large
(unsigned) LinuxVMAddress values that could not possibly refer to proper
addresses in a 32-bit process’ address space.
The offending reinterpret_cast<>() conversions have been replaced with
the new FromPointerCast<>(), which is careful to do sign-extension when
converting to a signed type, and zero-extension when converting to an
unsigned type like LinuxVMAddress.
Bug: crashpad:30
Test: crashpad_util_test FromPointerCast*:MemoryMap.*:ProcessMemory.*
Change-Id: I6f1408dc63369a8740ecd6015d657e4407a7c271
Reviewed-on: https://chromium-review.googlesource.com/488264
Reviewed-by: Joshua Peraza <jperaza@chromium.org>
