[HWASan] Use tagged-globals feature on x86.

[morehouse]

Summary

Allows us to use the small code model when we disable relocation
relaxation.

[eugenis]

LGTM

clang/lib/Driver/SanitizerArgs.cpp

CmdArgs.push_back(Args.MakeArgString(
         AsanDetectStackUseAfterReturnModeToString(AsanUseAfterReturn)));
   }
 
   if (!HwasanAbi.empty()) {
     CmdArgs.push_back("-default-function-attr");
     CmdArgs.push_back(Args.MakeArgString("hwasan-abi=" + HwasanAbi));
   }
 
-  if (Sanitizers.has(SanitizerKind::HWAddress) && TC.getTriple().isAArch64()) {
+  if (Sanitizers.has(SanitizerKind::HWAddress) && !HwasanUseAliases) {
     CmdArgs.push_back("-target-feature");
     CmdArgs.push_back("+tagged-globals");
   }
 
   // MSan: Workaround for PR16386.
   // ASan: This is mainly to help LSan with cases such as
   // https://github.com/google/sanitizers/issues/373
   // We can't make this conditional on -fsanitize=leak, as that flag shouldn't

compiler-rt/test/hwasan/TestCases/global.c

 // RUN: %clang_hwasan %s -o %t
 // RUN: %run %t 0
 // RUN: not %run %t 1 2>&1 | FileCheck --check-prefixes=CHECK,RSYM %s
 // RUN: not %env_hwasan_opts=symbolize=0 %run %t 1 2>&1 | FileCheck --check-prefixes=CHECK,RNOSYM %s
 // RUN: not %run %t -1 2>&1 | FileCheck --check-prefixes=CHECK,LSYM %s
 // RUN: not %env_hwasan_opts=symbolize=0 %run %t -1 2>&1 | FileCheck --check-prefixes=CHECK,LNOSYM %s
 
+// Test with and without optimizations, with and without PIC, since different
+// backend passes run depending on these flags.
+// RUN: %clang_hwasan -fno-pic %s -o %t
+// RUN: not %run %t 1 2>&1 | FileCheck --check-prefixes=CHECK,RSYM %s
+// RUN: %clang_hwasan -fno-pic -O2 %s -o %t
+// RUN: not %run %t 1 2>&1 | FileCheck --check-prefixes=CHECK,RSYM %s
+// RUN: %clang_hwasan -O2 %s -o %t
+// RUN: not %run %t 1 2>&1 | FileCheck --check-prefixes=CHECK,RSYM %s
+
 // REQUIRES: pointer-tagging
 
 int x = 1;
 
 int main(int argc, char **argv) {
   // CHECK: Cause: global-overflow
   // RSYM: is located 0 bytes to the right of 4-byte global variable x {{.*}} in {{.*}}global.c.tmp
   // RNOSYM: is located to the right of a 4-byte global variable in
   // RNOSYM-NEXT: #0 0x{{.*}} ({{.*}}global.c.tmp+{{.*}})
   // LSYM: is located 4 bytes to the left of 4-byte global variable x {{.*}} in {{.*}}global.c.tmp
   // LNOSYM: is located to the left of a 4-byte global variable in
   // LNOSYM-NEXT: #0 0x{{.*}} ({{.*}}global.c.tmp+{{.*}})
   // CHECK-NOT: can not describe
   (&x)[atoi(argv[1])] = 1;
 }

compiler-rt/test/hwasan/lit.cfg.py

 clang_cxxflags = config.cxx_mode_flags + clang_cflags
 clang_hwasan_common_cflags = clang_cflags + ["-fsanitize=hwaddress", "-fuse-ld=lld"]
 
 if config.target_arch == 'x86_64' and config.enable_aliases == '1':
   clang_hwasan_common_cflags += ["-fsanitize-hwaddress-experimental-aliasing"]
 else:
   config.available_features.add('pointer-tagging')
 if config.target_arch == 'x86_64':
-  # This does basically the same thing as tagged-globals on aarch64. Because
-  # the x86_64 implementation is for testing purposes only there is no
-  # equivalent target feature implemented on x86_64.
-  clang_hwasan_common_cflags += ["-mcmodel=large"]
+  # By default the assembler uses R_X86_64_REX_GOTPCRELX relocations, which can
+  # be relaxed to direct references.  When tagged globals are enabled, these
+  # references fail to link since they have more than a 32-bit offset from RIP.
+  # As a workaround, we disable the relaxation.
+  # TODO: Implement a way to disable for the affected relocations only.
+  clang_hwasan_common_cflags += ["-Wa,-mrelax-relocations=no"]
 
   # The callback instrumentation used on x86_64 has a 1/64 chance of choosing a
   # stack tag of 0.  This causes stack tests to become flaky, so we force tags
   # to be generated via calls to __hwasan_generate_tag, which never returns 0.
   # TODO: See if we can remove this once we use the outlined instrumentation.
   clang_hwasan_common_cflags += ["-mllvm", "-hwasan-generate-tags-with-calls=1"]
 clang_hwasan_cflags = clang_hwasan_common_cflags + ["-mllvm", "-hwasan-globals",
                                                    "-mllvm", "-hwasan-use-short-granules",