Initialize variables before assignment in asm

[protze.joachim]

Summary

When applying MemorySanitizer to an OpenMP application, msan complains about uninitialized access for these variables, which are assigned in assembler code. With these changes, I could successfully apply MemorySanitizer to an OpenMP application.

If the initialization is considered harmful, an alternative would be to wrap the initialization in

#if defined(__has_feature)
#  if __has_feature(memory_sanitizer)
// code that builds only under MemorySanitizer
#  endif
#endif

[jlpeyton]

Can you put a constructor in the kmp_cpuid structure inside kmp.h which initializes eax, ebx, ecx & edx to 0?

[jlpeyton]

Changing the state to request changes

runtime/src/kmp_affinity.cpp

static int __kmp_affinity_create_apicid_map(AddrUnsPair **address2os,
   return depth;
 }
 
 // Intel(R) microarchitecture code name Nehalem, Dunnington and later
 // architectures support a newer interface for specifying the x2APIC Ids,
 // based on cpuid leaf 11.
 static int __kmp_affinity_create_x2apicid_map(AddrUnsPair **address2os,
                                               kmp_i18n_id_t *const msg_id) {
-  kmp_cpuid buf;
+  kmp_cpuid buf = {0, 0, 0, 0};
   *address2os = NULL;
   *msg_id = kmp_i18n_null;
 
   // Check to see if cpuid leaf 11 is supported.
   __kmp_x86_cpuid(0, 0, &buf);
   if (buf.eax < 11) {
     *msg_id = kmp_i18n_str_NoLeaf11Support;
     return -1;

runtime/src/kmp_runtime.cpp

 }
 
 #if KMP_ARCH_X86 || KMP_ARCH_X86_64
 // Propagate any changes to the floating point control registers out to the team
 // We try to avoid unnecessary writes to the relevant cache line in the team
 // structure, so we don't make changes unless they are needed.
 inline static void propagateFPControl(kmp_team_t *team) {
   if (__kmp_inherit_fp_control) {
-    kmp_int16 x87_fpu_control_word;
-    kmp_uint32 mxcsr;
+    kmp_int16 x87_fpu_control_word = 0;
+    kmp_uint32 mxcsr = 0;
 
     // Get master values of FPU control flags (both X87 and vector)
     __kmp_store_x87_fpu_control_word(&x87_fpu_control_word);
     __kmp_store_mxcsr(&mxcsr);
     mxcsr &= KMP_X86_MXCSR_MASK;
 
     // There is no point looking at t_fp_control_saved here.
     // If it is TRUE, we still have to update the values if they are different

 }
 
 // Do the opposite, setting the hardware registers to the updated values from
 // the team.
 inline static void updateHWFPControl(kmp_team_t *team) {
   if (__kmp_inherit_fp_control && team->t.t_fp_control_saved) {
     // Only reset the fp control regs if they have been changed in the team.
     // the parallel region that we are exiting.
-    kmp_int16 x87_fpu_control_word;
-    kmp_uint32 mxcsr;
+    kmp_int16 x87_fpu_control_word = 0;
+    kmp_uint32 mxcsr = 0;
     __kmp_store_x87_fpu_control_word(&x87_fpu_control_word);
     __kmp_store_mxcsr(&mxcsr);
     mxcsr &= KMP_X86_MXCSR_MASK;
 
     if (team->t.t_x87_fpu_control_word != x87_fpu_control_word) {
       __kmp_clear_x87_fpu_status_word();
       __kmp_load_x87_fpu_control_word(&team->t.t_x87_fpu_control_word);
     }

runtime/src/kmp_utility.cpp

if (0 < value &&
     }
     result = value;
   }
   return result;
 
 } // func __kmp_parse_cpu_frequency
 
 void __kmp_query_cpuid(kmp_cpuinfo_t *p) {
-  struct kmp_cpuid buf;
+  struct kmp_cpuid buf = {0, 0, 0, 0};
   int max_arg;
   int log_per_phy;
 #ifdef KMP_DEBUG
   int cflush_size;
 #endif
 
   p->initialized = 1;