[AArch64][PAC][lldb] Support PAuth features in user expressions

[kovdan01]

This PR contains changes related to PAuth support in lldb (particularly, in lldb user expressions).

For implicitly signed stuff, we rely on correct LangOptions. They are set depending on the GNU_PROPERTY_AARCH64_FEATURE_PAUTH value, so the PR includes its support implementation at all levels. See:

• tools (llvm-readelf/llvm-readobj): c8d71df
• frontend: a0cc186
• backend: a3ddb4e
• lld: e4ff3bf
• lldb: aa37665

For explicitly signed stuff, we still need to set LangOptions properly, but we also need to parse the explicit signing schema from Dwarf. See:

• __ptrauth-qualified pointers: 8e62fa8
• [[clang::ptrauth_vtable_pointer(...)]] attribute: 8ed84bc
• [[clang::ptrauth_struct(...)]] attribute: 3a04a18

Any prefix of the patch series can be merged independently of the remaining suffix - when reset to any of the commits, all tests still pass and the functionality implemented in the commits from the prefix of the series works.

---

The PR contains tests for all the changes, but manual testing is also used since lldb unit tests might not be enough (at least unless we have lldb shell lit tests). See C/C++ code under spoilers and lldb session output while debugging corresponding executables below.

Free function pointer
source

int n = 0;

typedef void fptr();

void a() {
  n = 1;
}

fptr *b = &a;

int main() {
  b();
  return n;
}

lldb session

$ lldb ./freefun
(lldb) target create "./freefun"
Current executable set to '/path/to/freefun' (aarch64).
(lldb) b main
Breakpoint 1: where = freefun`main + 20 at freefun.c:12:3, address = 0x0000000000010770
(lldb) r
Process 3155439 launched: '/path/to/freefun' (aarch64)
Process 3155439 stopped
* thread #1, name = 'freefun', stop reason = breakpoint 1.1
    frame #0: 0x0000aaaaaaab0770 freefun`main at freefun.c:12:3
(lldb) p b
(fptr *) 0x0036aaaaaaab074c (actual=0x0000aaaaaaab074c freefun`a at freefun.c:6:5)
(lldb) p n
(int) 0
(lldb) expr b()
(lldb) p n
(int) 1

Member function pointer
source

int n = 0;

struct A {
  void foo() { n = 1; }
};

A a;

void (A::*fptr)() = &A::foo;

int main() {
  (a.*fptr)();
  return n;
}

lldb session

$ lldb ./member
(lldb) target create "./member"
Current executable set to '/path/to/member' (aarch64).
(lldb) b main
Breakpoint 1: where = member`main + 32 at member.cpp:12:7, address = 0x0000000000010774
(lldb) r
Process 3155481 launched: '/path/to/member' (aarch64)
Process 3155481 stopped
* thread #1, name = 'member', stop reason = breakpoint 1.1
    frame #0: 0x0000aaaaaaab0774 member`main at member.cpp:12:7
(lldb) p fptr
(void (A::*)()) 0x0000000000000000001aaaaaaaab0804 (actual=0x0000aaaaaaab0804 member`A::foo() at member-implicit.cpp:4)
(lldb) p n
(int) 0
(lldb) (a.*fptr)()
error: '(a.*fptr)()' is not a valid command.
(lldb) expr (a.*fptr)()
(lldb) p n
(int) 1

Virtual table pointer and virtual function pointer
source

int n = 0;

struct A {
  virtual void foo() { n = 1; }
};

A a;

int main() {
  a.foo();
  return n;
}

lldb session

$ lldb ./implicit/virt
(lldb) target create "./virt"
Current executable set to '/path/to/virt' (aarch64).
(lldb) b main
Breakpoint 1: where = virt`main + 20 at virt.cpp:10:5, address = 0x0000000000010818
(lldb) r
Process 3155530 launched: '/path/to/virt' (aarch64)
Process 3155530 stopped
* thread #1, name = 'virt', stop reason = breakpoint 1.1
    frame #0: 0x0000aaaaaaab0818 virt`main at virt.cpp:10:5
(lldb) p *(void**)(&a)
(void *) 0x0039aaaaaaac0900
(lldb) p *(void**)(0xaaaaaaac0900)
(void *) 0x0010aaaaaaab0838
(lldb) p n
(int) 0
(lldb) expr a.foo()
(lldb) p n
(int) 1

---

TODO:

• Add more manual tests in this description
• Distinguish naming for ELF and MachO PAuth ABI versioning