scc

commit 575a2d87cac49174b7f53aa6ac5f9186c2165697
parent cc00e16d081e5f802f046bc0a40ef597a4af1c0e
Author: Sören Tempel <soeren+git@soeren-tempel.net>
Date:   Wed, 19 Aug 2026 20:32:01 +0200

Don't specify a QBE return type for C functions with void return type

Without this patch, SCC currently emits QBE functions that have a "w"
return type for C functions that have a void return type. However, in
the return statement of these functions, it doesn't return a value.
Depending on the reader's interpretation, one could argue that this is
in violation of the QBE specification, which states: “All return values
of this function must have [the specified] return type” [1]. Arguably, a
ret instruction without an argument does not have a "w" return type.
qbe(1) itself accepts this, but other tooling built around QBE may not.

With this patch, functions with zero-sized types are now represented as
not having a return type in the QBE representation. Further, the emitted
QBE call instruction no longer assigns the return value of functions
with a void return type to a temporary.

This was discovered while executing SCC's emitted QBE representation
using quebex, a software analysis framework that comes with its own
standalone implementation of the QBE specification [2].

[1]: https://c9x.me/compile/doc/il.html#Functions
[2]: https://git.8pit.net/quebex

Diffstat:
M
src/cmd/scc-cc/cc2/qbe/code.c
 | 
10
+++++++---

1 file changed, 7 insertions(+), 3 deletions(-)
diff --git a/src/cmd/scc-cc/cc2/qbe/code.c b/src/cmd/scc-cc/cc2/qbe/code.c
@@ -411,7 +411,10 @@ writeout(void)
 
 	if (curfun->kind == SGLOB)
 		fputs("export ", stdout);
-	printf("function %s %s(", size2stack(&curfun->rtype), symname(curfun));
+	printf("function ");
+	if (curfun->rtype.size > 0)
+		printf("%s ", size2stack(&curfun->rtype));
+	printf("%s(", symname(curfun));
 
 	/* declare formal parameters */
 	sep = "";
@@ -519,8 +522,9 @@ call(void)
 
 	strcpy(to, addr2txt(&pc->to));
 	strcpy(from, addr2txt(&pc->from1));
-	printf("\t%s =%s\tcall\t%s(",
-	       to, size2stack(&sym->type), from);
+	if (sym->type.size > 0)
+		printf("\t%s =%s", to, size2stack(&sym->type));
+	printf("\tcall\t%s(", from);
 }
 
 static void