[libc-commits] [libc] [libc] Extend the baremetal I/O vendor ABI (PR #98683)

[Roland McGrath via libc-commits]

================
@@ -12,20 +12,52 @@
 
 namespace LIBC_NAMESPACE {
 
-// This is intended to be provided by the vendor.
+// These are intended to be provided by the vendor.
+//
+// The signature of these types and functions intentionally match `fopencookie`
+// which allows the following:
+//
+// ```
+// struct __llvm_libc_stdio_cookie __llvm_libc_stdin_cookie;
+// cookie_io_functions_t stdin_func = { .read = __llvm_libc_stdio_read };
+// FILE *stdin = fopencookie(&__llvm_libc_stdin_cookie, "r", stdin_func);
+// ...
+// struct __llvm_libc_stdio_cookie __llvm_libc_stdout_cookie;
+// cookie_io_functions_t stdout_func = { .write = __llvm_libc_stdio_write };
+// FILE *stdout = fopencookie(&__llvm_libc_stdout_cookie, "w", stdout_func);
+// ...
+// struct __llvm_libc_stdio_cookie __llvm_libc_stderr_cookie;
+// cookie_io_functions_t stderr_func = { .write = __llvm_libc_stdio_write };
+// FILE *stderr = fopencookie(&__llvm_libc_stderr_cookie, "w", stderr_func);
+// ```
+//
+// At the same time, implementation of functions like `printf` and `scanf` can
+// use `__llvm_libc_stdio_read` and `__llvm_libc_stdio_write` directly to avoid
+// the extra indirection.
 
-extern struct __llvm_libc_stdin __llvm_libc_stdin;
-extern "C" ssize_t __llvm_libc_stdin_read(void *cookie, char *buf, size_t size);
+struct __llvm_libc_stdio_cookie;
 
-extern "C" void __llvm_libc_log_write(const char *msg, size_t len);
+extern struct __llvm_libc_stdio_cookie __llvm_libc_stdin_cookie;
+extern struct __llvm_libc_stdio_cookie __llvm_libc_stdout_cookie;
+extern struct __llvm_libc_stdio_cookie __llvm_libc_stderr_cookie;
+
+extern "C" ssize_t __llvm_libc_stdio_read(void *cookie, char *buf, size_t size);
+extern "C" ssize_t __llvm_libc_stdio_write(void *cookie, const char *buf,
+                                           size_t size);
 
 ssize_t read_from_stdin(char *buf, size_t size) {
-  return __llvm_libc_stdin_read(reinterpret_cast<void *>(&__llvm_libc_stdin),
+  return __llvm_libc_stdio_read(static_cast<void *>(&__llvm_libc_stdin_cookie),
----------------
frobtech wrote:

The cast is superfluous but does no harm.


https://github.com/llvm/llvm-project/pull/98683