From a9e0174fb69f3ddc85cd9c510b68cec22b6ebf42 Mon Sep 17 00:00:00 2001
From: lemon <lsof@mailbox.org>
Date: Sun, 23 Nov 2025 15:26:55 +0100
Subject: c: __builtin_va_copy

---
 c/builtin.c       | 29 +++++++++++++++++++++--------
 embedfilesdir.c   |  2 +-
 test/10-varargs.c | 17 +++++++++++++++++
 3 files changed, 39 insertions(+), 9 deletions(-)

diff --git a/c/builtin.c b/c/builtin.c
index 23e1872..29a3191 100644
--- a/c/builtin.c
+++ b/c/builtin.c
@@ -24,11 +24,11 @@ callcheck(const struct span *span, int nparam, const union type *param, int narg
    return ok;
 }
 
-#define DEF_FNLIKE_SEMA(name, retty, ...)                                        \
-   static bool                                                                   \
-   name##_sema(struct comp *cm, struct expr *ex) {                               \
-      static union type par[] = { {{0}}, __VA_ARGS__ };                          \
-      ex->ty = retty;                                                            \
+#define DEF_FNLIKE_SEMA(name, retty, ...)                                          \
+   static bool                                                                     \
+   name##_sema(struct comp *cm, struct expr *ex) {                                 \
+      union type par[] = { {{0}}, __VA_ARGS__ };                                   \
+      ex->ty = retty;                                                              \
       return callcheck(&ex->span, arraylength(par)-1, par+1, ex->narg, ex->sub+1); \
    }
 
@@ -50,6 +50,8 @@ va_start_comp(struct function *fn, struct expr *ex, bool discard)
    return NOREF;
 }
 
+DEF_FNLIKE_SEMA(trap, mktype(TYVOID), )
+
 static bool
 va_end_sema(struct comp *cm, struct expr *ex)
 {
@@ -63,7 +65,19 @@ va_end_comp(struct function *fn, struct expr *ex, bool discard)
    return NOREF;
 }
 
-DEF_FNLIKE_SEMA(trap, mktype(TYVOID), )
+DEF_FNLIKE_SEMA(va_copy, mktype(TYVOID), cvalistty, cvalistty)
+
+static union ref
+va_copy_comp(struct function *fn, struct expr *ex, bool discard)
+{
+   union irtype typ = mkirtype(cvalistty.t == TYARRAY ? typechild(cvalistty) : cvalistty);
+   assert(ex->sub[1].ty.bits == cvalistty.bits);
+   assert(ex->sub[2].ty.bits == cvalistty.bits);
+   addinstr(fn, mkarginstr(typ, compileexpr(fn, &ex->sub[1], 0)));
+   addinstr(fn, mkarginstr(typ, compileexpr(fn, &ex->sub[2], 0)));
+   addinstr(fn, mkintrin(INstructcopy, 0, 2));
+   return NOREF;
+}
 
 static union ref
 trap_comp(struct function *fn, struct expr *ex, bool discard)
@@ -81,8 +95,7 @@ builtin_va_arg_comp(struct function *fn, const struct expr *ex, bool discard)
 }
 
 #define LIST_BUILTINS(_) \
-   _(va_start) \
-   _(va_end) \
+   _(va_start) _(va_copy) _(va_end) \
    _(trap)
 
 static const struct {
diff --git a/embedfilesdir.c b/embedfilesdir.c
index d2670b3..05d65d0 100644
--- a/embedfilesdir.c
+++ b/embedfilesdir.c
@@ -27,7 +27,7 @@ typedef __builtin_va_list __gnuc_va_list;\n\
 #endif\n\
 #define va_start(ap,n)   __builtin_va_start(ap)\n\
 #define va_arg(ap,type)  __builtin_va_arg(ap, type)\n\
-#define va_copy(dst,src) (void)((dst)=(src))\n\
+#define va_copy(dst,src) __builtin_va_copy(dst, src)\n\
 #define va_end(ap)       __builtin_va_end(ap)\n\
 ")},
 
diff --git a/test/10-varargs.c b/test/10-varargs.c
index a3715ab..a523d97 100644
--- a/test/10-varargs.c
+++ b/test/10-varargs.c
@@ -2,6 +2,8 @@
 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 = 36
 <1.5>
 1.1 + 2.1 + 3.1 + 5.1 + 1.5 + -1.5 + 1.5 + -1.5 + 1.5 + -1 = 11.9
+fwd()/1: Hello World
+fwd()/2: Hello World
 */
 
 
@@ -37,9 +39,24 @@ double sumf(double x, ...) {
    return x;
 }
 
+void fwd(const char *fmt, ...) {
+   va_list ap, aq;
+   va_start(ap, fmt);
+   va_copy(aq, ap);
+   printf("fwd()/1: ");
+   vprintf(fmt, ap);
+   va_end(ap);
+   printf("\n");
+   printf("fwd()/2: ");
+   vprintf(fmt, aq);
+   printf("\n");
+   va_end(aq);
+}
+
 
 int main() {
    printf(" = %d\n", sum(1,2,3,4,5,6,7,8,0,0));
    printf("<%g>\n", stkarg(0,0,0,0,0,0,0,0,1.5));
    printf(" = %g\n", sumf(1.1, 2.1, 3.1, 5.1, 1.5, -1.5, 1.5, -1.5, 1.5, -1.0, 0.0));
+   fwd("%s %s", "Hello", "World");
 }
-- 
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