Update output for timestamp with llvm-readobj on XCOFF files.

[stephenpeckham]

Summary

The llvm-readobj prints extra characters for the timestamp when --file-headers is used with an XCOFF file. This change updates the format string used to print the time. In addition, the timestamp is printed in the local timezone, and a thread-safe call is used to convert the time.

[jhenderson]

llvm/tools/llvm-readobj/XCOFFDumper.cpp

105

This is failing to build on Windows.

[stephenpeckham]

This update backs out the changes except for removing the extra characters. WIthout a Windows system, the changes to use localtime_r() and update the test case are not practical. It would be nice to have a common function to print timestamps for all object file formats.

[jhenderson]

LGTMing this, to clear my objection, but I'm not a user of XCOFF, so I'd like one of the developers who regularly works on this to take a look too before this lands.

@Esme/@DiggerLin, any comments from either of you two?

@stephenpeckham, don't forget to update your commit message if you're dropping the localtime_r stuff.

[DiggerLin]

LGTM

llvm/test/tools/llvm-readobj/XCOFF/file-header.test

 ## This is a general test for the --file-header option.
 
 # RUN: yaml2obj %s -o %t1
-# RUN: llvm-readobj %t1 --file-header | \
+# RUN: TZ=GMT llvm-readobj %t1 --file-header | \
 # RUN:   FileCheck %s --strict-whitespace --match-full-lines --check-prefix=FILEHEADER32
 
 #      FILEHEADER32:Format: aixcoff-rs6000
 # FILEHEADER32-NEXT:Arch: powerpc
 # FILEHEADER32-NEXT:AddressSize: 32bit
 # FILEHEADER32-NEXT:FileHeader {
 # FILEHEADER32-NEXT:  Magic: 0x1DF
 # FILEHEADER32-NEXT:  NumberOfSections: 1
-# FILEHEADER32-NEXT:  TimeStamp: 1970-01-01T00:00:01Z (0x1)
+# FILEHEADER32-NEXT:  TimeStamp: 1970-01-01 00:00:01 GMT (0x1)
 # FILEHEADER32-NEXT:  SymbolTableOffset: 0x3C
 # FILEHEADER32-NEXT:  SymbolTableEntries: 1
 # FILEHEADER32-NEXT:  OptionalHeaderSize: 0x0
 # FILEHEADER32-NEXT:  Flags: 0x12
 # FILEHEADER32-NEXT:}
 
 --- !XCOFF
 FileHeader:

llvm/tools/llvm-readobj/XCOFFDumper.cpp

void XCOFFDumper::printFileHeaders() {
   // Negative timestamp values are reserved for future use.
   int32_t TimeStamp = Obj.getTimeStamp();
   if (TimeStamp > 0) {
     // This handling of the time stamp assumes that the host system's time_t is
     // compatible with AIX time_t. If a platform is not compatible, the lit
     // tests will let us know.
     time_t TimeDate = TimeStamp;
 
-    char FormattedTime[21] = {};
-    size_t BytesWritten =
-        strftime(FormattedTime, 21, "%Y-%m-%dT%H:%M:%SZ", gmtime(&TimeDate));
-    if (BytesWritten)
+    char FormattedTime[80] = {};
+    struct tm local_tm;
+    size_t BytesFormatted =
+        strftime(FormattedTime, sizeof(FormattedTime), "%F %T %Z",
+                 localtime_r(&TimeDate, &local_tm));
+    if (BytesFormatted)
       W.printHex("TimeStamp", FormattedTime, TimeStamp);
     else
       W.printHex("Timestamp", TimeStamp);
   } else {
     W.printHex("TimeStamp", TimeStamp == 0 ? "None" : "Reserved Value",
                TimeStamp);
   }