From ad6f17cd93fb5d505240802d6cf53a285086594f Mon Sep 17 00:00:00 2001
From: Rangi <remy.oukaour+rangi42@gmail.com>
Date: Wed, 16 Dec 2020 11:08:18 -0500
Subject: [PATCH] Support SOURCE_DATE_EPOCH for reproducible builds

See https://reproducible-builds.org/docs/source-date-epoch/

Fixes #286
---
 include/asm/symbol.h |  3 ++-
 src/asm/main.c       | 14 ++++++++++++--
 src/asm/rgbasm.5     |  6 ++++++
 src/asm/symbol.c     |  4 +---
 4 files changed, 21 insertions(+), 6 deletions(-)

diff --git a/include/asm/symbol.h b/include/asm/symbol.h
index f9005bc2..63578234 100644
--- a/include/asm/symbol.h
+++ b/include/asm/symbol.h
@@ -12,6 +12,7 @@
 #include <stdbool.h>
 #include <stdint.h>
 #include <string.h>
+#include <time.h>
 
 #include "asm/section.h"
 
@@ -140,7 +141,7 @@ struct Symbol *sym_AddMacro(char const *symName, int32_t defLineNo, char *body,
 struct Symbol *sym_Ref(char const *symName);
 struct Symbol *sym_AddString(char const *symName, char const *value);
 void sym_Purge(char const *symName);
-void sym_Init(void);
+void sym_Init(time_t now);
 
 /* Functions to save and restore the current symbol scope. */
 char const *sym_GetCurrentSymbolScope(void);
diff --git a/src/asm/main.c b/src/asm/main.c
index 47ee0019..16a251f6 100644
--- a/src/asm/main.c
+++ b/src/asm/main.c
@@ -218,7 +218,7 @@ static char *make_escape(const char *str)
 }
 
 /* Short options */
-static char const *optstring = "b:D:Eg:hi:LM:o:p:r:VvW:w";
+static const char *optstring = "b:D:Eg:hi:LM:o:p:r:VvW:w";
 
 /* Variables for the long-only options */
 static int depType; /* Variants of `-M` */
@@ -283,6 +283,16 @@ int main(int argc, char *argv[])
 
 	char *tzMainfile;
 
+	time_t now = time(NULL);
+	char *sourceDateEpoch = getenv("SOURCE_DATE_EPOCH");
+
+	/*
+	 * Support SOURCE_DATE_EPOCH for reproducible builds
+	 * https://reproducible-builds.org/docs/source-date-epoch/
+	 */
+	if (sourceDateEpoch)
+		now = (time_t)strtoul(sourceDateEpoch, NULL, 0);
+
 	dependfile = NULL;
 
 	/* Initial number of allocated elements in array */
@@ -481,7 +491,7 @@ int main(int argc, char *argv[])
 
 	nTotalLines = 0;
 	nIFDepth = 0;
-	sym_Init();
+	sym_Init(now);
 	sym_SetExportAll(exportall);
 
 	opt_ParseDefines();
diff --git a/src/asm/rgbasm.5 b/src/asm/rgbasm.5
index 568d1d68..d787d4fb 100644
--- a/src/asm/rgbasm.5
+++ b/src/asm/rgbasm.5
@@ -1092,6 +1092,12 @@ The following symbols are defined by the assembler:
 .It Ic EQU Ta Dv __RGBDS_MINOR__ Ta Minor version number of RGBDS
 .It Ic EQU Ta Dv __RGBDS_PATCH__ Ta Patch version number of RGBDS
 .El
+.Pp
+The current time values will be taken from the
+.Dv SOURCE_DATE_EPOCH
+environment variable if that is defined as a UNIX timestamp.
+Refer to the spec at
+.Lk https://reproducible-builds.org/docs/source-date-epoch/ .
 .Sh DEFINING DATA
 .Ss Declaring variables in a RAM section
 .Ic DS
diff --git a/src/asm/symbol.c b/src/asm/symbol.c
index 3ce5c221..699bbb4d 100644
--- a/src/asm/symbol.c
+++ b/src/asm/symbol.c
@@ -655,7 +655,7 @@ static inline struct Symbol *createBuiltinSymbol(char const *name)
 /*
  * Initialize the symboltable
  */
-void sym_Init(void)
+void sym_Init(time_t now)
 {
 	PCSymbol = createBuiltinSymbol("@");
 	struct Symbol *_NARGSymbol = createBuiltinSymbol("_NARG");
@@ -677,8 +677,6 @@ void sym_Init(void)
 	sym_AddEqu("__RGBDS_MINOR__", PACKAGE_VERSION_MINOR)->isBuiltin = true;
 	sym_AddEqu("__RGBDS_PATCH__", PACKAGE_VERSION_PATCH)->isBuiltin = true;
 
-	time_t now = time(NULL);
-
 	if (now == (time_t)-1) {
 		warn("Couldn't determine current time");
 		/* Fall back by pretending we are at the Epoch */