Improve linker script align (#1271)

An offset is now supported, and invalid values are no longer silently
truncated, aligning behaviour with other instances of the directive.

man/rgblink.5

@@ -68,15 +68,25 @@ and
 .Ic DS :
 .Bl -bullet
 .It
-.Ic ORG
+.Ic ORG Ar addr
-sets the address in which new sections will be placed.
+sets the address in which new sections will be placed to
+.Ar addr .
 It can not be lower than the current address.
 .It
-.Ic ALIGN
+.Ic ALIGN Ar addr
+or
+.Ic ALIGN Ar addr , Ar offset
 will increase the address until it is aligned to the specified boundary
-.Po it tries to set to 0 the number of bits specified after the directive:
+.Po it tries to set to
+.Ar offset
+the number of bits specified by
+.Ar align :
+for example,
 .Ql ALIGN 8
-will align to $100
+will align to $100 ,
+and
+.Ql ALIGN 8 , 10
+will align to $10A
 .Pc .
 .It
 .Ic DS

src/link/script.y

@@ -51,6 +51,7 @@
 
 %token YYEOF 0 "end of file"
 %token newline
+%token COMMA ","
 %token ORG "ORG"
        INCLUDE "INCLUDE"
        ALIGN "ALIGN"
@@ -83,6 +84,7 @@ directive: section_type { setSectionType($1); }
          | section_type number { setSectionType($1, $2); }
          | ORG number { setAddr($2); }
          | ALIGN number { alignTo($2, 0); }
+         | ALIGN number COMMA number { alignTo($2, $4); }
          | DS number { pad($2); }
          | string { placeSection($1); }
 ;
@@ -197,6 +199,8 @@ try_again: // Can't use a `do {} while(0)` loop, otherwise compilers (wrongly) t
 		} else {
 			return yy::parser::make_YYEOF();
 		}
+	} else if (c == ',') {
+		return yy::parser::make_COMMA();
 	} else if (isNewline(c)) {
 		// Handle CRLF.
 		if (c == '\r' && context.file.sgetc() == '\n') {
@@ -372,18 +376,37 @@ static void alignTo(uint32_t alignment, uint32_t alignOfs) {
 	auto const &typeInfo = sectionTypeInfo[activeType];
 	auto &pc = curAddr[activeType][activeBankIdx];
 
-	// TODO: maybe warn if truncating?
+	if (alignment > 16) {
-	alignOfs %= 1 << alignment;
+		scriptError(context, "Cannot align: The alignment (%" PRIu32 ") must be less than 16\n",
+			    alignment);
+		return;
+	}
+
+	// Let it wrap around, this'll trip the final check if alignment == 16.
+	uint16_t length = alignOfs - pc;
+
+	if (alignment < 16) {
+		uint32_t alignSize = 1u << alignment;
+
+		if (alignOfs >= alignSize) {
+			scriptError(context, "Cannot align: The alignment offset (%" PRIu32
+					      ") must be less than alignment size (%" PRIu32 ")\n",
+				    alignOfs, 1 << alignment);
+			return;
+		}
 
 		assert(pc >= typeInfo.startAddr);
-	uint16_t length = alignment < 16 ? (uint16_t)(alignOfs - pc) % (1u << alignment)
+		length %= alignSize;
-	                                 : alignOfs - pc; // Let it wrap around, this'll trip the check.
-	if (uint16_t offset = pc - typeInfo.startAddr; length > typeInfo.size - offset) {
-		scriptError(context, "Cannot align: the next suitable address after $%04" PRIx16 " is $%04" PRIx16 ", past $%04" PRIx16,
-		            pc, (uint16_t)(pc + length), (uint16_t)(endaddr(activeType) + 1));
-	} else {
-		pc += length;
 	}
+
+	if (uint16_t offset = pc - typeInfo.startAddr; length > typeInfo.size - offset) {
+		scriptError(context, "Cannot align: the next suitable address after $%04"
+				     PRIx16 " is $%04" PRIx16 ", past $%04" PRIx16,
+			    pc, (uint16_t)(pc + length), (uint16_t)(endaddr(activeType) + 1));
+		return;
+	}
+
+	pc += length;
 }
 
 static void pad(uint32_t length) {

test/link/section-attributes-mismatch.out

@@ -1,2 +1,2 @@
-error: ./section-attributes-mismatch.link(3): The linker script assigns section "sec" to address $0018, but that would be ALIGN[4, 8] instead of the requested ALIGN[4, 0]
+error: ./section-attributes-mismatch.link(3): The linker script assigns section "sec" to address $0018, but that would be ALIGN[4, 8] instead of the requested ALIGN[4, 2]
 Linking failed with 1 error

test/link/section-attributes.asm

@@ -1,3 +1,3 @@
-SECTION "sec",ROM0,ALIGN[4]
+SECTION "sec",ROM0,ALIGN[4,2]
-	ds 8, $42
+	ds 6, $42
 SECTION "secfix",ROM0[$20]

test/link/section-attributes.link

@@ -1,6 +1,7 @@
 ROM0
-	align 4
+	align 4, 2
 	"sec"
 	ds $18
 	org $20
+	align 5
 	"secfix"