From 28bfd02af512f572aaa1255332ca95bf363da05e Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Wed, 25 Mar 2026 16:42:24 +0300
Subject: [PATCH] cgen: fix compilation with -freestanding missing main (fixes
 #20227)

---
 vlib/builtin/linux_bare/libc_impl.v             |  2 +-
 vlib/v/gen/c/fn.v                               | 17 ++++++++++++++++-
 ...freestanding_memcpy_declarations.c.must_have |  6 ++++++
 .../freestanding_memcpy_declarations.vv         |  2 ++
 4 files changed, 25 insertions(+), 2 deletions(-)
 create mode 100644 vlib/v/gen/c/testdata/freestanding_memcpy_declarations.c.must_have
 create mode 100644 vlib/v/gen/c/testdata/freestanding_memcpy_declarations.vv

diff --git a/vlib/builtin/linux_bare/libc_impl.v b/vlib/builtin/linux_bare/libc_impl.v
index 7a1cc2a4e..3054a44fa 100644
--- a/vlib/builtin/linux_bare/libc_impl.v
+++ b/vlib/builtin/linux_bare/libc_impl.v
@@ -25,7 +25,7 @@ fn __malloc(n usize) voidptr {
 
 @[export: 'strlen']
 @[unsafe]
-fn strlen(const_s &char) usize {
+fn strlen(const_s voidptr) usize {
 	s := unsafe { &u8(const_s) }
 	mut i := 0
 	for ; unsafe { s[i] } != 0; i++ {}
diff --git a/vlib/v/gen/c/fn.v b/vlib/v/gen/c/fn.v
index 568a78f5e..5ee0e8923 100644
--- a/vlib/v/gen/c/fn.v
+++ b/vlib/v/gen/c/fn.v
@@ -1505,7 +1505,12 @@ fn (mut g Gen) fn_decl_params(params []ast.Param, scope &ast.Scope, is_variadic
 			} else {
 				''
 			}
-			s := '${const_prefix}${param_type_name} ${var_name_prefix}${caname}'
+			const_param_type_name := if const_prefix != '' {
+				g.const_pointer_param_type_name(typ, param_type_name)
+			} else {
+				param_type_name
+			}
+			s := '${const_prefix}${const_param_type_name} ${var_name_prefix}${caname}'
 			if !g.inside_c_extern {
 				g.write(s)
 			}
@@ -1530,6 +1535,16 @@ fn (mut g Gen) fn_decl_params(params []ast.Param, scope &ast.Scope, is_variadic
 	return fparams, fparamtypes, heap_promoted
 }
 
+fn (mut g Gen) const_pointer_param_type_name(typ ast.Type, param_type_name string) string {
+	unwrapped_typ := g.unwrap_generic(typ)
+	return match unwrapped_typ {
+		ast.voidptr_type { 'void*' }
+		ast.byteptr_type { 'u8*' }
+		ast.charptr_type { 'char*' }
+		else { param_type_name }
+	}
+}
+
 fn (mut g Gen) get_anon_fn_type_name(mut node ast.AnonFn, var_name string) string {
 	mut builder := strings.new_builder(64)
 	return_styp := g.styp(node.decl.return_type)
diff --git a/vlib/v/gen/c/testdata/freestanding_memcpy_declarations.c.must_have b/vlib/v/gen/c/testdata/freestanding_memcpy_declarations.c.must_have
new file mode 100644
index 000000000..dc0952adb
--- /dev/null
+++ b/vlib/v/gen/c/testdata/freestanding_memcpy_declarations.c.must_have
@@ -0,0 +1,6 @@
+void *memcpy(void *dest, const void *src, size_t n);
+void *memmove(void *dest, const void *src, size_t n);
+VV_EXP voidptr memcpy(voidptr dest, const void* const_src, usize n);
+VV_EXP voidptr memmove(voidptr dest, const void* const_src, usize n);
+VV_EXP int memcmp(const void* const_a, const void* const_b, usize n);
+VV_EXP usize strlen(const void* const_s);
diff --git a/vlib/v/gen/c/testdata/freestanding_memcpy_declarations.vv b/vlib/v/gen/c/testdata/freestanding_memcpy_declarations.vv
new file mode 100644
index 000000000..e59812a3b
--- /dev/null
+++ b/vlib/v/gen/c/testdata/freestanding_memcpy_declarations.vv
@@ -0,0 +1,2 @@
+// vtest vflags: -freestanding
+fn main() {}
-- 
2.39.5