[RISCV][ASAN] Fix TLS offsets

[luismarques]

Summary

This fixes an ASan test failure: TestCases/Linux/static_tls.cpp.
The original code was introduced by rG809a42e3d535.

[luismarques]

NFC

[luismarques]

compiler-rt/lib/sanitizer_common/sanitizer_linux_libcdep.cpp

379–381

(I would use __builtin_thread_pointer, but IIRC that's not supported by GCC for RISC-V, and the code for the sanitizers is shared between codebases)

[EccoTheDolphin]

LGTM

[lenary]

compiler-rt/lib/sanitizer_common/sanitizer_linux_libcdep.cpp

379–381

We should leave a TODO, I think we've (recently) agreed that __builtin_thread_pointer will always return tp.

[kito-cheng]

compiler-rt/lib/sanitizer_common/sanitizer_linux_libcdep.cpp

379–381

RISC-V GCC has implemented __builtin_thread_pointer, so I think it's fine to use that.

https://github.com/gcc-mirror/gcc/commit/1073b500e5d33af8b75567108a8c04fe2598df2b

[luismarques]

Use __builtin_thread_pointer.

[luismarques]

Thanks for the info @kito-cheng

compiler-rt/lib/sanitizer_common/sanitizer_linux_libcdep.cpp

asm volatile(".set push;\
                 .set mips64r2;\
                 rdhwr %0,$29;\
                 .set pop" : "=r" (thread_pointer));
   descr_addr = thread_pointer - kTlsTcbOffset - TlsPreTcbSize();
 #elif defined(__aarch64__) || defined(__arm__)
   descr_addr = reinterpret_cast<uptr>(__builtin_thread_pointer()) -
                                       ThreadDescriptorSize();
 #elif SANITIZER_RISCV64
-  uptr tcb_end;
-  asm volatile("mv %0, tp;\n" : "=r"(tcb_end));
   // https://github.com/riscv/riscv-elf-psabi-doc/issues/53
-  const uptr kTlsTcbOffset = 0x800;
-  descr_addr =
-      reinterpret_cast<uptr>(tcb_end - kTlsTcbOffset - TlsPreTcbSize());
+  uptr thread_pointer = reinterpret_cast<uptr>(__builtin_thread_pointer());
+  descr_addr = thread_pointer - TlsPreTcbSize();
 #elif defined(__s390__)
   descr_addr = reinterpret_cast<uptr>(__builtin_thread_pointer());
 #elif defined(__powerpc64__)
   // PPC64LE uses TLS variant I. The thread pointer (in GPR 13)
   // points to the end of the TCB + 0x7000. The pthread_descr structure is
   // immediately in front of the TCB. TlsPreTcbSize() includes the size of the
   // TCB and the size of pthread_descr.
   const uptr kTlsTcbOffset = 0x7000;
   uptr thread_pointer;

compiler-rt/lib/sanitizer_common/sanitizer_tls_get_addr.cpp

void DTLS_Destroy() {
   uptr s = dtls.dtv_size;
   dtls.dtv_size = kDestroyedThread;  // Do this before unmap for AS-safety.
   DTLS_Deallocate(dtls.dtv, s);
 }
 
 #if defined(__powerpc64__) || defined(__mips__)
 // This is glibc's TLS_DTV_OFFSET:
 // "Dynamic thread vector pointers point 0x8000 past the start of each
-//  TLS block."
+//  TLS block." (sysdeps/<arch>/dl-tls.h)
 static const uptr kDtvOffset = 0x8000;
+#elif defined(__riscv)
+// This is glibc's TLS_DTV_OFFSET:
+// "Dynamic thread vector pointers point 0x800 past the start of each
+// TLS block." (sysdeps/riscv/dl-tls.h)
+static const uptr kDtvOffset = 0x800;
 #else
 static const uptr kDtvOffset = 0;
 #endif
 
 DTLS::DTV *DTLS_on_tls_get_addr(void *arg_void, void *res,
                                 uptr static_tls_begin, uptr static_tls_end) {
   if (!common_flags()->intercept_tls_get_addr) return 0;
   TlsGetAddrParam *arg = reinterpret_cast<TlsGetAddrParam *>(arg_void);