Fix for Pointer Authentication

[bgaechter]

Properly strip PAC signatures from an arm64 process

Description of changes:
The build on Apple M1 notebooks currently fails with the following errors
/src/backward.h:4032:64: error: no member named 'pc' in '__darwin_mcontext64' error_addr = reinterpret_cast<void*>(uctx->uc_mcontext.pc);

src/backward.h:4032:63: error: member reference type 'struct __darwin_mcontext64 *' is a pointer; did you mean to use '->'? error_addr = reinterpret_cast<void*>(uctx->uc_mcontext.pc);

This is happens because of PAC. This change handles PAC and make the code compile again on M1 Macbooks.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[bmoffatt]

Confirmed that this works on my M1 Mac. Before merging, I also want to check that this works on Linux aarch64, as that's not currently covered by the test workflows

[bmoffatt]

yeah that did not go well on Linux/aarch64!

bryan@air aws-lambda-cpp % docker run --rm -it -v `pwd`:/src public.ecr.aws/amazonlinux/amazonlinux:2
bash-4.2# yum install -q -y curl-devel openssl-devel gcc-c++ ninja-build cmake3
Delta RPMs disabled because /usr/bin/applydeltarpm not installed.
bash-4.2# cmake3 -S /src -B /src/build -G Ninja
-- The CXX compiler identification is GNU 7.3.1
-- Check for working CXX compiler: /usr/bin/c++
-- Check for working CXX compiler: /usr/bin/c++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Found CURL: /usr/lib64/libcurl.so (found version "7.79.1")
-- Looking for backtrace
-- Looking for backtrace - found
-- backtrace facility detected in default set of libraries
-- Found Backtrace: /usr/include
-- Configuring done
-- Generating done
-- Build files have been written to: /src/build
bash-4.2# cmake3 --build /src/build
[4/5] Building CXX object CMakeFiles/aws-lambda-runtime.dir/src/backward.cpp.o
FAILED: CMakeFiles/aws-lambda-runtime.dir/src/backward.cpp.o
/usr/bin/c++  -DAWS_LAMBDA_LOG=0 -I../include -flto -fno-fat-lto-objects   -fno-exceptions -fno-rtti -fvisibility=hidden -fvisibility-inlines-hidden -Wall -Wextra -Werror -Wconversion -Wno-sign-conversion -std=gnu++11 -MD -MT CMakeFiles/aws-lambda-runtime.dir/src/backward.cpp.o -MF CMakeFiles/aws-lambda-runtime.dir/src/backward.cpp.o.d -o CMakeFiles/aws-lambda-runtime.dir/src/backward.cpp.o -c ../src/backward.cpp
In file included from ../src/backward.cpp:26:0:
../src/backward.h: In static member function 'static void backward::SignalHandling::handleSignal(int, siginfo_t*, void*)':
../src/backward.h:4032:63: error: base operand of '->' has non-pointer type 'mcontext_t {aka sigcontext}'
         error_addr = reinterpret_cast<void*>(uctx->uc_mcontext->__ss.__pc);
                                                               ^~
ninja: build stopped: subcommand failed.
bash-4.2# uname -a
Linux 7f7d47b6b999 5.10.104-linuxkit #1 SMP PREEMPT Thu Mar 17 17:05:54 UTC 2022 aarch64 aarch64 aarch64 GNU/Linux

Needs more ifdef!

Probably a fresh update of backward.h is actually what we want

[bmoffatt]

This should be resolved now with #154