Use architecture-specific va_list type

Previously, cproc effectively used used

	typedef struct { /* 32 bytes, 8-byte aligned */ } __builtin_va_list[1];

However, this is not quite correct for x86_64 nor aarch64, though
it was close enough for both to work in most cases.

In actuality, for x86_64 we want

	typedef struct { /* 24 bytes, 8-byte aligned */ } __builtin_va_list[1];

and for aarch64 we want

	typedef struct { /* 32 bytes, 8-byte aligned */ } __builtin_va_list;

The difference only appears when the size of va_list matters, or
when va_list is passed as a parameter. However, the former is not
often the case, and the aarch64 ABI replaces aggregate arguments
with pointers to caller-allocated memory, which is quite similar
to arrays decaying to pointers in C except that the struct is not
copied.

Additionally, riscv64 simply uses

	typedef void *__builtin_va_list;

which again has a different size and calling convention.

To fix this, make the __builtin_va_list type architecture-specific
and use architecture-specific tests for varargs-related functionality.

1 files changed, 4 insertions, 0 deletions

diff --git a/qbe.c b/qbe.c
index df363c2..be7dce7 100644
--- a/qbe.c
+++ b/qbe.c
@@ -1104,6 +1104,10 @@ emittype(struct type *t)
 	}
 	fputs("type ", stdout);
 	emitvalue(t->value);
+	if (t == targ->typevalist) {
+		printf(" = align %d { %" PRIu64 " }\n", t->align, t->size);
+		return;
+	}
 	fputs(" = { ", stdout);
 	for (m = t->structunion.members, off = 0; m;) {
 		if (t->kind == TYPESTRUCT) {