[sanitizer] Print errno for report file open failure

[tejohnson]

Summary

To help debug failures, specifically the llvm-avr-linux bot failure from
5c20d7db9f2791367b9311130eb44afecb16829c:

http://lab.llvm.org:8011/#/builders/112/builds/407/steps/5/logs/FAIL__MemProfiler-x86_64-linux-dynamic__log_path_t

Also re-enable the failing test which I temporarily disabled, to
see if this change will help identify why that particular log file can't
be opened for write on that bot (when another log file in the same
directory could earlier in the test).

[vitalybuka]

compiler-rt/lib/sanitizer_common/sanitizer_file.cpp

68

[vitalybuka]

Fails on bot http://lab.llvm.org:8011/#/builders/37/builds/275

[tejohnson]

In D90120#2363238, @vitalybuka wrote:

Fails on bot http://lab.llvm.org:8011/#/builders/37/builds/275

Yep, saw that one fail too. And finally figured out the issue after staring at the paths again. Its due to macro expansion of the "linux" in the path name with "1" in the path specified to PROFILE_VAR_NAME, since the bot has "-linux" in its name and therefore the path. I've disabled the test again in rGd124ac0c223a, with an explanation of what is going on. I can reproduce it locally on my linux box when I manually compile the test with -DPROFILE_VAR_NAME set to a path with "-linux" in it. I'm not sure how to prevent multiple levels of macros from being expanded in the stringizing sequence. I might just have it pass a hardcoded bad path and test that it gets passed through (via one of the errors like I am checking with CHECK-INVALID).

compiler-rt/lib/sanitizer_common/sanitizer_file.cpp

void ReportFile::ReopenIfNecessary() {
 
   const char *exe_name = GetProcessName();
   if (common_flags()->log_exe_name && exe_name) {
     internal_snprintf(full_path, kMaxPathLength, "%s.%s.%zu", path_prefix,
                       exe_name, pid);
   } else {
     internal_snprintf(full_path, kMaxPathLength, "%s.%zu", path_prefix, pid);
   }
-  fd = OpenFile(full_path, WrOnly);
+  error_t err;
+  fd = OpenFile(full_path, WrOnly, &err);
   if (fd == kInvalidFd) {
     const char *ErrorMsgPrefix = "ERROR: Can't open file: ";
     WriteToFile(kStderrFd, ErrorMsgPrefix, internal_strlen(ErrorMsgPrefix));
     WriteToFile(kStderrFd, full_path, internal_strlen(full_path));
+    char errmsg[100];
+    internal_snprintf(errmsg, sizeof(errmsg), " (reason: %d)", err);
+    WriteToFile(kStderrFd, errmsg, internal_strlen(errmsg));
     Die();
   }
   fd_pid = pid;
 }
 
 void ReportFile::SetReportPath(const char *path) {
   if (path) {
     uptr len = internal_strlen(path);

compiler-rt/test/memprof/TestCases/log_path_test.cpp

 // Invalid log_path.
 // RUN: %env_memprof_opts=log_path=/dev/null/INVALID not %run %t 2>&1 | FileCheck %s --check-prefix=CHECK-INVALID --dump-input=always
 
 // Too long log_path.
 // RUN: %env_memprof_opts=log_path=`for((i=0;i<10000;i++)); do echo -n $i; done` \
 // RUN:   not %run %t 2>&1 | FileCheck %s --check-prefix=CHECK-LONG --dump-input=always
 
 // Specifying the log name via the __memprof_profile_filename variable.
-// TODO: Temporarily disabled due to llvm-avr-linux bot failure
-// %clangxx_memprof  %s -o %t -DPROFILE_NAME_VAR="%t.log2"
-// rm -f %t.log2.*
-// %run %t
-// FileCheck %s --check-prefix=CHECK-GOOD --dump-input=always < %t.log2.*
+// RUN: %clangxx_memprof  %s -o %t -DPROFILE_NAME_VAR="%t.log2"
+// RUN: rm -f %t.log2.*
+// RUN: %run %t
+// RUN: FileCheck %s --check-prefix=CHECK-GOOD --dump-input=always < %t.log2.*
 
 #ifdef PROFILE_NAME_VAR
 #define xstr(s) str(s)
 #define str(s) #s
 char __memprof_profile_filename[] = xstr(PROFILE_NAME_VAR);
 #endif
 
 #include <stdlib.h>