[lld] [LLD] [COFF] Pick timestamps from the SOURCE_DATE_EPOCH variable (PR #81326)

[Martin Storsjö via llvm-commits]

https://github.com/mstorsjo created https://github.com/llvm/llvm-project/pull/81326

The SOURCE_DATE_EPOCH environment variable can be set in order to get reproducible build.

When linking PE/COFF modules with LLD, the timestamp field is set to the current time, unless either the /timestamp: or /Brepro option is set. If neither of them is set, check the SOURCE_DATE_EPOCH variable, before resorting to using the actual current date and time.

>From 1e8254e60bad8f8a2286daedd41dd36660e757f6 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Martin=20Storsj=C3=B6?= <martin at martin.st>
Date: Sat, 10 Feb 2024 00:36:16 +0200
Subject: [PATCH] [LLD] [COFF] Pick timestamps from the SOURCE_DATE_EPOCH
 variable

The SOURCE_DATE_EPOCH environment variable can be set in order
to get reproducible build.

When linking PE/COFF modules with LLD, the timestamp field is
set to the current time, unless either the /timestamp: or
/Brepro option is set. If neither of them is set, check the
SOURCE_DATE_EPOCH variable, before resorting to using the
actual current date and time.
---
 lld/COFF/Driver.cpp          | 10 +++++++++-
 lld/test/COFF/timestamp.test |  2 ++
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/lld/COFF/Driver.cpp b/lld/COFF/Driver.cpp
index e0afb6b18805b2..22ee2f133be98a 100644
--- a/lld/COFF/Driver.cpp
+++ b/lld/COFF/Driver.cpp
@@ -1825,7 +1825,15 @@ void LinkerDriver::linkerMain(ArrayRef<const char *> argsArr) {
     }
   } else {
     config->repro = false;
-    config->timestamp = time(nullptr);
+    if (std::optional<std::string> epoch =
+            Process::GetEnv("SOURCE_DATE_EPOCH")) {
+      StringRef value(*epoch);
+      if (value.getAsInteger(0, config->timestamp))
+        fatal(Twine("invalid SOURCE_DATE_EPOCH timestamp: ") + value +
+              ".  Expected 32-bit integer");
+    } else {
+      config->timestamp = time(nullptr);
+    }
   }
 
   // Handle /alternatename
diff --git a/lld/test/COFF/timestamp.test b/lld/test/COFF/timestamp.test
index fbdc5788a33a55..f94eeee8793f01 100644
--- a/lld/test/COFF/timestamp.test
+++ b/lld/test/COFF/timestamp.test
@@ -3,9 +3,11 @@ RUN: yaml2obj %p/Inputs/generic.yaml -o %t.obj
 RUN: lld-link %t.obj /debug /Brepro /entry:main /nodefaultlib /out:%t.1.exe
 RUN: lld-link %t.obj /debug /Brepro /entry:main /nodefaultlib /out:%t.2.exe
 RUN: lld-link %t.obj /debug /timestamp:0 /entry:main /nodefaultlib /out:%t.3.exe
+RUN: env SOURCE_DATE_EPOCH=0 lld-link %t.obj /debug /entry:main /nodefaultlib /out:%t.4.exe
 RUN: llvm-readobj --file-headers --coff-debug-directory %t.1.exe | FileCheck %s --check-prefix=HASH
 RUN: llvm-readobj --file-headers --coff-debug-directory %t.2.exe | FileCheck %s --check-prefix=HASH
 RUN: llvm-readobj --file-headers --coff-debug-directory %t.3.exe | FileCheck %s --check-prefix=ZERO
+RUN: llvm-readobj --file-headers --coff-debug-directory %t.4.exe | FileCheck %s --check-prefix=ZERO
 
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