[lld-macho] Flip ZERO_AR_DATE default

[keith]

Summary

Previously unless ZERO_AR_DATE was set to any value, ld64.lld would
embed non-hermetic timestamps into the final binary. This flips that
default to zero those values unless ZERO_AR_DATE is set explicitly to 0.
As far as I know there isn't a downside to this, except that it differs
from ld64.

[keith]

I don't feel strongly about this if folks think we just shouldn't differ here, it just seems like the right default. For reference even though llvm-ar has D it defaults to this behavior as well.

[int3]

Fine by me. Can we document this in the ld64-vs-lld.rst doc?

[keith]

Include difference in docs

[int3]

lgtm

lld/docs/MachO/ld64-vs-lld.rst

64

[keith]

Formatting

lld/MachO/Config.h

struct Configuration {
   SymbolPatterns unexportedSymbols;
   SymbolPatterns whyLive;
 
   std::vector<std::pair<llvm::StringRef, llvm::StringRef>> aliasedSymbols;
 
   SymtabPresence localSymbolsPresence = SymtabPresence::All;
   SymbolPatterns localSymbolPatterns;
 
-  bool zeroModTime = false;
+  bool zeroModTime = true;
 
   llvm::StringRef osoPrefix;
 
   std::vector<llvm::StringRef> dyldEnvs;
 
   llvm::MachO::Architecture arch() const { return platformInfo.target.Arch; }
 
   llvm::MachO::PlatformType platform() const {

lld/MachO/Driver.cpp

for (const Arg *arg : args.filtered(OPT_ignore_auto_link_option))
     config->ignoreAutoLinkOptions.insert(arg->getValue());
 
   for (const Arg *arg : args.filtered(OPT_alias)) {
     config->aliasedSymbols.push_back(
         std::make_pair(arg->getValue(0), arg->getValue(1)));
   }
 
   // FIXME: Add a commandline flag for this too.
-  config->zeroModTime = getenv("ZERO_AR_DATE");
+  if (const char *zero = getenv("ZERO_AR_DATE"))
+    config->zeroModTime = strcmp(zero, "0") != 0;
 
   std::array<PlatformType, 3> encryptablePlatforms{
       PLATFORM_IOS, PLATFORM_WATCHOS, PLATFORM_TVOS};
   config->emitEncryptionInfo =
       args.hasFlag(OPT_encryptable, OPT_no_encryption,
                    is_contained(encryptablePlatforms, config->platform()));
 
 #ifndef LLVM_HAVE_LIBXAR

lld/docs/MachO/ld64-vs-lld.rst

 Aliases
 =======
 ld64 treats all aliases as strong extern definitions. Having two aliases of the
 same name, or an alias plus a regular extern symbol of the same name, both
 result in duplicate symbol errors. LLD does not check for duplicate aliases;
 instead we perform alias resolution first, and only then do we check for
 duplicate symbols. In particular, we will not report a duplicate symbol error if
 the aliased symbols turn out to be weak definitions, but ld64 will.
+
+``ZERO_AR_DATE`` enabled by default
+***********************************
+ld64 has a special mode where it sets some stabs modification times to 0 for
+hermetic builds, enabled by setting any value for the ``ZERO_AR_DATE``
+environment variable. LLD flips this default to perfer hermetic builds, but
+allows disabling this behavior by setting ``ZERO_AR_DATE=0``. Any other value
+of ``ZERO_AR_DATE`` will be ignored.

lld/test/MachO/lto-object-path.ll

 ; REQUIRES: x86
 ; UNSUPPORTED: system-windows
 
 ; RUN: rm -rf %t; mkdir %t
 ; RUN: opt -thinlto-bc %s -o %t/test.o
 
 ; RUN: %lld %t/test.o -o %t/test
 ; RUN: llvm-nm -pa %t/test | FileCheck %s --check-prefixes CHECK,NOOBJPATH
 
-; RUN: %lld %t/test.o -o %t/test -object_path_lto %t/lto-temps
+; RUN: ZERO_AR_DATE=0 %lld %t/test.o -o %t/test -object_path_lto %t/lto-temps
 ; RUN: llvm-nm -pa %t/test | FileCheck %s --check-prefixes CHECK,OBJPATH-DIR -DDIR=%t/lto-temps
 
 ;; Ensure object path is still used if the cache is used
-; RUN: %lld %t/test.o -o %t/test -object_path_lto %t/lto-temps -prune_interval_lto 20 -cache_path_lto %t/cache --thinlto-cache-policy=cache_size_files=1:cache_size_bytes=10
+; RUN: ZERO_AR_DATE=0 %lld %t/test.o -o %t/test -object_path_lto %t/lto-temps -prune_interval_lto 20 -cache_path_lto %t/cache --thinlto-cache-policy=cache_size_files=1:cache_size_bytes=10
 ; RUN: llvm-nm -pa %t/test | FileCheck %s --check-prefixes CHECK,OBJPATH-DIR -DDIR=%t/lto-temps
 ;; And that dsymutil can read the result
 ; RUN: dsymutil -f -o - %t/test | llvm-dwarfdump - | FileCheck %s --check-prefix=DSYM
 
 ;; Test that the object path hardlinks to the cache when possible
-;; NB: 
+;; NB:
 ;; 1) Need to delete current object path contents or hardlink will fail.
 ;; 2) Note the cache policy is different from the test above (which is crafted
 ;;    to ensure that the cache is pruned immediately; we want the opposite here).
 ; RUN: rm -rf %t/lto-temps
 ; RUN: %lld %t/test.o -o %t/test -object_path_lto %t/lto-temps -prune_interval_lto 20 -cache_path_lto %t/cache --thinlto-cache-policy=cache_size_files=10:cache_size_bytes=10000
 ;; Get the link count.
 ; RUN: ls -l %t/lto-temps/1.x86_64.lto.o | tr -s ' ' | cut -f 2 -d ' ' | FileCheck %s --check-prefix=HARDLINK
 
 ;; check that the object path can be an existing file
 ; RUN: touch %t/lto-tmp.o
-; RUN: %lld %t/test.o -o %t/test -object_path_lto %t/lto-tmp.o
+; RUN: ZERO_AR_DATE=0 %lld %t/test.o -o %t/test -object_path_lto %t/lto-tmp.o
 ; RUN: llvm-nm -pa %t/test | FileCheck %s --check-prefixes CHECK,OBJPATH-FILE -DFILE=%t/lto-tmp.o
 
 
 ; CHECK:             0000000000000000                - 00 0000    SO /tmp/test.cpp
 ; NOOBJPATH-NEXT:    0000000000000000                - 03 0001   OSO /tmp/lto.tmp
 ;; check that modTime is nonzero when `-object_path_lto` is provided
 ; OBJPATH-DIR-NEXT:  {{[0-9a-f]*[1-9a-f]+[0-9a-f]*}} - 03 0001   OSO [[DIR]]/1.x86_64.lto.o
 ; OBJPATH-FILE-NEXT: {{[0-9a-f]*[1-9a-f]+[0-9a-f]*}} - 03 0001   OSO [[FILE]]

lld/test/MachO/stabs.s

 # REQUIRES: x86, shell
 # UNSUPPORTED: system-windows
 # RUN: rm -rf %t; split-file %s %t
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/test.s -o %t/test.o
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/foo.s -o %t/foo.o
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/no-debug.s -o %t/no-debug.o
 ## Set modtimes of the files for deterministic test output.
 # RUN: env TZ=UTC touch -t "197001010000.16" %t/test.o
 # RUN: env TZ=UTC touch -t "197001010000.32" %t/foo.o
 # RUN: llvm-ar rcsU %t/foo.a %t/foo.o
 
-# RUN: %lld -lSystem %t/test.o %t/foo.o %t/no-debug.o -o %t/test
+# RUN: ZERO_AR_DATE=0 %lld -lSystem %t/test.o %t/foo.o %t/no-debug.o -o %t/test
 # RUN: (llvm-objdump --section-headers %t/test; dsymutil -s %t/test) | \
 # RUN:   FileCheck %s -DDIR=%t -DFOO_PATH=%t/foo.o \
 # RUN:       -D#TEST_TIME=0x10 -D#FOO_TIME=0x20
 
 ## Check that we emit the right modtime even when the object file is in an
 ## archive.
-# RUN: %lld -lSystem %t/test.o %t/foo.a %t/no-debug.o -o %t/test
+# RUN: ZERO_AR_DATE=0 %lld -lSystem %t/test.o %t/foo.a %t/no-debug.o -o %t/test
 # RUN: (llvm-objdump --section-headers %t/test; dsymutil -s %t/test) | \
 # RUN:   FileCheck %s -DDIR=%t -DFOO_PATH=%t/foo.a\(foo.o\) \
 # RUN:       -D#TEST_TIME=0x10 -D#FOO_TIME=0x20
 
 ## Check that we don't emit modtimes if ZERO_AR_DATE is set.
 # RUN: env ZERO_AR_DATE=1 %lld -lSystem %t/test.o %t/foo.o %t/no-debug.o \
 # RUN:     -o %t/test
 # RUN: (llvm-objdump --section-headers %t/test; dsymutil -s %t/test) | \
 # RUN:   FileCheck %s -DDIR=%t -DFOO_PATH=%t/foo.o \
 # RUN:       -D#TEST_TIME=0 -D#FOO_TIME=0
-# RUN: env ZERO_AR_DATE=1 %lld -lSystem %t/test.o %t/foo.a %t/no-debug.o \
+# RUN: env %lld -lSystem %t/test.o %t/foo.a %t/no-debug.o \
 # RUN:     -o %t/test
 # RUN: (llvm-objdump --section-headers %t/test; dsymutil -s %t/test) | \
 # RUN:   FileCheck %s -DDIR=%t -DFOO_PATH=%t/foo.a\(foo.o\) \
 # RUN:       -D#TEST_TIME=0 -D#FOO_TIME=0
-# RUN: env ZERO_AR_DATE=1 %lld -lSystem %t/test.o %t/no-debug.o \
+# RUN: env %lld -lSystem %t/test.o %t/no-debug.o \
 # RUN:     -all_load %t/foo.a -o %t/test
 # RUN: (llvm-objdump --section-headers %t/test; dsymutil -s %t/test) | \
 # RUN:   FileCheck %s -DDIR=%t -DFOO_PATH=%t/foo.a\(foo.o\) \
 # RUN:       -D#TEST_TIME=0 -D#FOO_TIME=0
-# RUN: env ZERO_AR_DATE=1 %lld -lSystem %t/test.o %t/no-debug.o \
+# RUN: env %lld -lSystem %t/test.o %t/no-debug.o \
 # RUN:     -force_load %t/foo.a -o %t/test
 # RUN: (llvm-objdump --section-headers %t/test; dsymutil -s %t/test) | \
 # RUN:   FileCheck %s -DDIR=%t -DFOO_PATH=%t/foo.a\(foo.o\) \
 # RUN:       -D#TEST_TIME=0 -D#FOO_TIME=0
 
 ## Check that we emit absolute paths to the object files in our OSO entries
 ## even if our inputs are relative paths.
-# RUN: cd %t && %lld -lSystem test.o foo.o no-debug.o -o test
+# RUN: cd %t && ZERO_AR_DATE=0 %lld -lSystem test.o foo.o no-debug.o -o test
 # RUN: (llvm-objdump --section-headers %t/test; dsymutil -s %t/test) | \
 # RUN:   FileCheck %s -DDIR=%t -DFOO_PATH=%t/foo.o \
 # RUN:       -D#TEST_TIME=0x10 -D#FOO_TIME=0x20
 
 ## Check that we emit relative path to object files in OSO entries
 ## when -oso_prefix <path> is used.
-# RUN: cd %t && %lld -lSystem test.o foo.o no-debug.o -oso_prefix "%t" -o %t/test-rel
+# RUN: cd %t && ZERO_AR_DATE=0 %lld -lSystem test.o foo.o no-debug.o -oso_prefix "%t" -o %t/test-rel
 # RUN: dsymutil -s  %t/test-rel | grep 'N_OSO' | FileCheck %s  -D#TEST_TIME=0x10 -D#FOO_TIME=0x20 --check-prefix=REL-PATH
-# RUN: cd %t && %lld -lSystem test.o foo.o no-debug.o -oso_prefix "%t/" -o %t/test-rel
+# RUN: cd %t && ZERO_AR_DATE=0 %lld -lSystem test.o foo.o no-debug.o -oso_prefix "%t/" -o %t/test-rel
 # RUN: dsymutil -s  %t/test-rel | grep 'N_OSO' | FileCheck %s  -D#TEST_TIME=0x10 -D#FOO_TIME=0x20 --check-prefix=REL-PATH-NO-SLASH
-# RUN: cd %t && %lld -lSystem test.o foo.o no-debug.o -oso_prefix "." -o %t/test-rel-dot
+# RUN: cd %t && ZERO_AR_DATE=0 %lld -lSystem test.o foo.o no-debug.o -oso_prefix "." -o %t/test-rel-dot
 # RUN: dsymutil -s  %t/test-rel-dot | grep 'N_OSO' | FileCheck %s  -D#TEST_TIME=0x10 -D#FOO_TIME=0x20 --check-prefix=REL-DOT
 ## Set HOME to %t (for ~ to expand to)
-# RUN: cd %t && env HOME=%t %lld -lSystem test.o foo.o no-debug.o -oso_prefix "~" -o %t/test-rel-tilde
+# RUN: cd %t && env HOME=%t ZERO_AR_DATE=0 %lld -lSystem test.o foo.o no-debug.o -oso_prefix "~" -o %t/test-rel-tilde
 # RUN: dsymutil -s  %t/test-rel-tilde | grep 'N_OSO' | FileCheck %s  -D#TEST_TIME=0x10 -D#FOO_TIME=0x20 --check-prefix=REL-PATH
 
 ## Check that we don't emit DWARF or stabs when -S is used
 # RUN: %lld -lSystem test.o foo.o no-debug.o -S -o %t/test-no-debug
 ## grep returns an exit code of 1 if it cannot match the intended pattern. We
 ## expect to not find any entries which requires the exit code to be negated.
 # RUN: llvm-nm -ap %t/test-no-debug | not grep -e ' - '
 
-# RUN: cd %t && %lld -lSystem test.o foo.a no-debug.o -o %t/test
+# RUN: cd %t && ZERO_AR_DATE=0 %lld -lSystem test.o foo.a no-debug.o -o %t/test
 # RUN: (llvm-objdump --section-headers %t/test; dsymutil -s %t/test) | \
 # RUN:   FileCheck %s -DDIR=%t -DFOO_PATH=%t/foo.a\(foo.o\) \
 # RUN:       -D#TEST_TIME=0x10 -D#FOO_TIME=0x20
 
 # CHECK:       Sections:
 # CHECK-NEXT:  Idx                Name
 # CHECK-NEXT:  [[#TEXT_ID:]]      __text
 # CHECK-NEXT:  [[#DATA_ID:]]      __data