Fix detection of backtrace() availability on FreeBSD

[arichardson]

Summary

On FreeBSD backtrace is not part of libc and depends on libexecinfo being
available. Instead of using manual checks we can use the builtin CMake
module FindBacktrace.cmake to detect availability of backtrace() in a
portable way.

[dim]

LGTM.

[emaste]

FYI I added libexecinfo before FreeBSD 10 so all supported FreeBSD releases have it.

[krytarowski]

Does NetBSD need it too?

Backtrace seems to work for me..

(lldb) bt
* thread #1, stop reason = step over
  * frame #0: 0x00007816c08f3eaf libc.so.12`fopen(file="", mode="") at fopen.c:116
    frame #1: 0x0000000096e0b0d2 phantasia`main at main.c:317
    frame #2: 0x0000000096e0b047 phantasia`main(argc=1, argv=0x00007f7fff162b48) at main.c:95
    frame #3: 0x0000000096e0203b phantasia`___start + 229

[theraven]

It's probably worth having Joerg look at this, as I believe a similar fix is needed on NetBSD.

[krytarowski]

Right, it's no LLDB....

For detecting libexecinfo please go for: Backtrace_LIBRARY It will handle FreeBSD and NetBSD

[krytarowski]

https://github.com/Kitware/CMake/blob/master/Modules/FindBacktrace.cmake

[arichardson]

Use FindBacktrace.cmake instead

[krytarowski]

Thanks, I'm going to test it.

[arichardson]

I noticed that the backtraces are not particularly useful on FreeBSD, they always look like this (even when I disable sigaltstack()):

#0 0x000000080183d35c llvm::sys::PrintStackTrace(llvm::raw_ostream&) /exports/users/alr48/sources/llvm-upstream/lib/Support/Unix/Signals.inc:399:11
#1 0x000000080183d799 PrintStackTraceSignalHandler(void*) /exports/users/alr48/sources/llvm-upstream/lib/Support/Unix/Signals.inc:463:1
#2 0x000000080183a797 llvm::sys::RunSignalHandlers(void) /exports/users/alr48/sources/llvm-upstream/lib/Support/Signals.cpp:45:5
#3 0x000000080183da0a SignalHandler(int) /exports/users/alr48/sources/llvm-upstream/lib/Support/Unix/Signals.inc:253:1
#4 0x0000000801aa778f (/lib/libthr.so.3+0xe78f)
#5 0x0000000801aa6d6f (/lib/libthr.so.3+0xdd6f)

I hacked around this issue by printing the stacktrace prior to calling abort but there must be a better solution.

[krytarowski]

Build for me:

NetBSD chieftec 7.99.66 NetBSD 7.99.66 (GENERIC) #6: Wed Mar 29 21:21:19 CEST 2017  root@chieftec:/public/netbsd-root/sys/arch/amd64/compile/GENERIC amd64

$ grep  -i backtrace CMakeCache.txt    
//Header providing backtrace(3) facility
Backtrace_HEADER:STRING=execinfo.h
Backtrace_INCLUDE_DIR:PATH=/usr/include
Backtrace_LIBRARY:FILEPATH=/usr/lib/libexecinfo.so
//Enable embedding backtraces on crash.
LLVM_ENABLE_BACKTRACES:BOOL=ON
//ADVANCED property for variable: Backtrace_HEADER
Backtrace_HEADER-ADVANCED:INTERNAL=1
//ADVANCED property for variable: Backtrace_INCLUDE_DIR
Backtrace_INCLUDE_DIR-ADVANCED:INTERNAL=1
//ADVANCED property for variable: Backtrace_LIBRARY
Backtrace_LIBRARY-ADVANCED:INTERNAL=1
//Details about finding Backtrace
FIND_PACKAGE_MESSAGE_DETAILS_Backtrace:INTERNAL=[/usr/lib/libexecinfo.so][/usr/include][v()]
//Have symbol _Unwind_Backtrace
HAVE__UNWIND_BACKTRACE:INTERNAL=1
//Have symbol backtrace
_Backtrace_SYM_FOUND:INTERNAL=

[arichardson]

I don't have commit access, could someone commit for me?

cmake/config-ix.cmake

 
 check_library_exists(xar xar_open "" HAVE_LIBXAR)
 if(HAVE_LIBXAR)
   set(XAR_LIB xar)
 endif()
 
 # function checks
 check_symbol_exists(arc4random "stdlib.h" HAVE_DECL_ARC4RANDOM)
+if(CMAKE_SYSTEM MATCHES "FreeBSD")
+  list(APPEND CMAKE_REQUIRED_LIBRARIES "execinfo")
+endif()
 check_symbol_exists(backtrace "execinfo.h" HAVE_BACKTRACE)
 check_symbol_exists(_Unwind_Backtrace "unwind.h" HAVE__UNWIND_BACKTRACE)
 check_symbol_exists(getpagesize unistd.h HAVE_GETPAGESIZE)
 check_symbol_exists(sysconf unistd.h HAVE_SYSCONF)
 check_symbol_exists(getrusage sys/resource.h HAVE_GETRUSAGE)
 check_symbol_exists(setrlimit sys/resource.h HAVE_SETRLIMIT)
 check_symbol_exists(isatty unistd.h HAVE_ISATTY)
 check_symbol_exists(futimens sys/stat.h HAVE_FUTIMENS)

lib/Support/CMakeLists.txt

elseif( CMAKE_HOST_UNIX )
   endif()
   set(system_libs ${system_libs} ${LLVM_PTHREAD_LIB})
   if ( LLVM_ENABLE_ZLIB AND HAVE_LIBZ )
     set(system_libs ${system_libs} z)
   endif()
   if( UNIX AND NOT (BEOS OR HAIKU) )
     set(system_libs ${system_libs} m)
   endif()
+  if (HAVE_BACKTRACE AND CMAKE_SYSTEM MATCHES "FreeBSD")
+    set(system_libs ${system_libs} execinfo)
+  endif()
 endif( MSVC OR MINGW )
 
 add_llvm_library(LLVMSupport
   APFloat.cpp
   APInt.cpp
   APSInt.cpp
   ARMBuildAttrs.cpp
   ARMAttributeParser.cpp

lib/Support/Unix/Signals.inc

 #include <mach/mach.h>
 #endif
 #if HAVE_LINK_H
 #include <link.h>
 #endif
 #ifdef HAVE__UNWIND_BACKTRACE
 // FIXME: We should be able to use <unwind.h> for any target that has an
 // _Unwind_Backtrace function, but on FreeBSD the configure test passes
-// despite the function not existing, and on Android, <unwind.h> conflicts
-// with <link.h>.
+// despite the function not existing unless _GNU_SOURCE is defined, and
+// on Android, <unwind.h> conflicts with <link.h>.
 #ifdef __GLIBC__
 #include <unwind.h>
 #else
 #undef HAVE__UNWIND_BACKTRACE
 #endif
 #endif
 
 using namespace llvm;