perform ucontext->pc variants testing in compile-time

As part of cpu profiler we're extracting current PC (program counter)
of out signal's ucontext. Different OS and hardware combinations have
different ways for that. We had a list of variants that we tested at
compile time and populated PC_FROM_UCONTEXT macro into config.h. It
caused duplication and occasional mismatches between our autoconf and
cmake bits.

So this commit changes testing to be compile-time. We remove
complexity from build system and add some to C++ source.

We use SFINAE to find which of those variants compile (and we silently
assume that 'compiles' implies 'works'; this is what config-time
testing did too). Occasionally we'll face situations where several
variants compile. And we couldn't handle this case in pure C++. So we
have a small Ruby program that generates chain of inheritance among
SFINAE-specialized class templates. This handles prioritization among
variants.

List of ucontext->pc extraction variants is mostly same. We dropped
super-obsolete (circa Linux kernel 2.0) arm variant. And NetBSD case
is now improved. We now use their nice architecture-independent macro
instead of x86-specific access.

CMakeLists.txt

@@ -60,7 +60,6 @@ include(GNUInstallDirs)
 
 list(APPEND CMAKE_MODULE_PATH ${CMAKE_CURRENT_SOURCE_DIR}/cmake)
 include(DefineTargetVariables)
-include(PCFromUContext)
 
 define_target_variables()
 
@@ -191,6 +190,9 @@ check_include_file("grp.h" HAVE_GRP_H) # for heapchecker_unittest
 check_include_file("pwd.h" HAVE_PWD_H) # for heapchecker_unittest
 check_include_file("sys/resource.h" HAVE_SYS_RESOURCE_H) # for memalign_unittest.cc
 check_include_file("sys/cdefs.h" HAVE_SYS_CDEFS_H) # Where glibc defines __THROW
+check_include_file("ucontext.h" HAVE_UCONTEXT_H)
+check_include_file("sys/ucontext.h" HAVE_SYS_UCONTEXT_H)
+check_include_file("cygwin/signal.h" HAVE_CYGWIN_SIGNAL_H)
 
 check_include_file("unistd.h" HAVE_UNISTD_H)
 # We also need <ucontext.h>/<sys/ucontext.h>, but we get those from
@@ -220,16 +222,6 @@ if(NOT WIN32)
   set(HAVE_MMAP 1)
 endif()
 
-# We want to access the "PC" (Program Counter) register from a struct
-# ucontext.  Every system has its own way of doing that.  We try all the
-# possibilities we know about.  Note REG_PC should come first (REG_RIP
-# is also defined on solaris, but does the wrong thing).  But don't
-# bother if we're not doing cpu-profiling.
-# [*] means that we've not actually tested one of these systems
-if (GPERFTOOLS_BUILD_CPU_PROFILER)
-  pc_from_ucontext(PC_FROM_UCONTEXT_DEF)
-endif ()
-
 # Some tests test the behavior of .so files, and only make sense for dynamic.
 option(GPERFTOOLS_BUILD_STATIC "Enable Static" ON)
 

cmake/config.h.in

@@ -206,9 +206,6 @@
 /* Define to the version of this package. */
 #define PACKAGE_VERSION "@PROJECT_VERSION@"
 
-/* How to access the PC from a struct ucontext */
-#define PC_FROM_UCONTEXT @PC_FROM_UCONTEXT_DEF@
-
 /* Always the empty-string on non-windows systems. On windows, should be
    "__declspec(dllexport)". This way, when we compile the dll, we export our
    functions/classes. It's safe to define this here because config.h is only

configure.ac

@@ -270,8 +270,11 @@ AC_CHECK_HEADERS(grp.h)         # for heapchecker_unittest
 AC_CHECK_HEADERS(pwd.h)         # for heapchecker_unittest
 AC_CHECK_HEADERS(sys/resource.h)         # for memalign_unittest.cc
 AC_CHECK_HEADERS(sys/cdefs.h)   # Where glibc defines __THROW
-# We also need <ucontext.h>/<sys/ucontext.h>, but we get those from
-# AC_PC_FROM_UCONTEXT, below.
+
+AC_CHECK_HEADERS(sys/ucontext.h)
+AC_CHECK_HEADERS(ucontext.h)
+AC_CHECK_HEADERS(cygwin/signal.h)        # ucontext on cywgin
+AC_CHECK_HEADERS(asm/ptrace.h)           # get ptrace macros, e.g. PT_NIP
 
 # check for socketpair, some system, such as QNX, need link in an socket library to use it
 AC_SEARCH_LIBS([socketpair], [socket])
@@ -305,14 +308,14 @@ case "$host" in
 esac
 
 # We want to access the "PC" (Program Counter) register from a struct
-# ucontext.  Every system has its own way of doing that.  We try all the
-# possibilities we know about.  Note REG_PC should come first (REG_RIP
-# is also defined on solaris, but does the wrong thing).  But don't
-# bother if we're not doing cpu-profiling.
-# [*] means that we've not actually tested one of these systems
+# ucontext.  Every system has its own way of doing that. But in case
+# we're dealing with unknown system, we have to check if GetPC
+# actually works. But don't bother if we're not doing cpu-profiling.
 if test "$enable_cpu_profiler" = yes; then
-  AC_PC_FROM_UCONTEXT(AC_MSG_WARN(Could not find the PC.  Will not try to compile libprofiler...);
-                      enable_cpu_profiler=no)
+  AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include "src/getpc.h"]], [GetPC({})])],
+                    [],
+                    [AC_MSG_WARN(Could not find the PC.  Will not try to compile libprofiler...)
+                     enable_cpu_profiler=no])
 fi
 
 # Some tests test the behavior of .so files, and only make sense for dynamic.