[compiler-rt] TlsBaseAddr value for darwin arm64

[devnexen]

Summary

getting the tls base address. unlike linux arm64, the tpidr_el0 returns always 0 (aka unused) thus using tpidrro_el0 instead clearing up the cpu id encoded in the lower bits.

[yln]

Hi David, thanks for the patch! :)

I have no objections; before landing, can you help me understand and document in the commit message which problem this is solving or what it is improving?
I see that TlsBaseAddr() now also returns a non-zero value for arm64 and that it is only used in GetThreadStackAndTls() which has a couple of callers.

void GetThreadStackAndTls(bool main, uptr *stk_addr, uptr *stk_size, uptr *tls_addr, uptr *tls_size);

[yln]

Note, I am getting the following warning when compiling your patch:

compiler-rt/lib/sanitizer_common/sanitizer_mac.cpp:559:36: warning: value size does not match register size specified by the constraint and modifier [-Wasm-operand-widths]
  asm("mrs %0, tpidrro_el0" : "=r"(segbase));
                                   ^
compiler-rt/lib/sanitizer_common/sanitizer_mac.cpp:559:12: note: use constraint modifier "w"
  asm("mrs %0, tpidrro_el0" : "=r"(segbase));
           ^~
           %w0

[devnexen]

In D112866#3115965, @yln wrote:

Note, I am getting the following warning when compiling your patch:

compiler-rt/lib/sanitizer_common/sanitizer_mac.cpp:559:36: warning: value size does not match register size specified by the constraint and modifier [-Wasm-operand-widths]
  asm("mrs %0, tpidrro_el0" : "=r"(segbase));
                                   ^
compiler-rt/lib/sanitizer_common/sanitizer_mac.cpp:559:12: note: use constraint modifier "w"
  asm("mrs %0, tpidrro_el0" : "=r"(segbase));
           ^~
           %w0

the warning is weird, I do not get this on my mac M1 arm64, compiled with Xcode clang.

[devnexen]

In D112866#3115965, @yln wrote:

Note, I am getting the following warning when compiling your patch:

compiler-rt/lib/sanitizer_common/sanitizer_mac.cpp:559:36: warning: value size does not match register size specified by the constraint and modifier [-Wasm-operand-widths]
  asm("mrs %0, tpidrro_el0" : "=r"(segbase));
                                   ^
compiler-rt/lib/sanitizer_common/sanitizer_mac.cpp:559:12: note: use constraint modifier "w"
  asm("mrs %0, tpidrro_el0" : "=r"(segbase));
           ^~
           %w0

hopefully the last diff clears the warning even tough should be unnecessary.

[yln]

Are there any tests that now pass (but didn't before)?

[devnexen]

next step would be the tlssize.

compiler-rt/lib/sanitizer_common/sanitizer_mac.cpp

 }
 
 uptr TlsBaseAddr() {
   uptr segbase = 0;
 #if defined(__x86_64__)
   asm("movq %%gs:0,%0" : "=r"(segbase));
 #elif defined(__i386__)
   asm("movl %%gs:0,%0" : "=r"(segbase));
+#elif defined(__aarch64__)
+  asm("mrs %0, tpidrro_el0" : "=r"(segbase));
+  segbase &= 0x07ul;  // clearing lower bits, cpu id stored there
 #endif
   return segbase;
 }
 
 // The size of the tls on darwin does not appear to be well documented,
 // however the vm memory map suggests that it is 1024 uptrs in size,
 // with a size of 0x2000 bytes on x86_64 and 0x1000 bytes on i386.
 uptr TlsSize() {
 #if defined(__x86_64__) || defined(__i386__)