sd-boot: terminal handling tweaks (#39026)

Let's make sd-boot's terminal handling a bit cleaner, to the point that
uefi's weird handling allows this.

src/boot/boot.c

@@ -495,8 +495,9 @@ static bool menu_run(
         ST->ConIn->Reset(ST->ConIn, false);
         ST->ConOut->EnableCursor(ST->ConOut, false);
 
-        /* draw a single character to make ClearScreen work on some firmware */
-        ST->ConOut->OutputString(ST->ConOut, (char16_t *) u" ");
+        /* Draw a single character to the beginning of a line, in order to make ClearScreen() work on certain
+         * broken firmware. And let's immediately move back to the beginning of the line. */
+        printf("\r \r");
 
         err = console_set_mode(config->console_mode_efivar != CONSOLE_MODE_KEEP ?
                                config->console_mode_efivar : config->console_mode);

src/boot/efi-string.c

@@ -917,6 +917,37 @@ static bool handle_format_specifier(FormatContext *ctx, SpecifierContext *sp) {
         }
 }
 
+#if SD_BOOT
+static void output_string_safe(EFI_SIMPLE_TEXT_OUTPUT_PROTOCOL *this, const char16_t *s) {
+        assert(this);
+        assert(s);
+
+        /* This is a color-conscious version of ST->ConOut->OutputString(). Whenever it encounters a newline
+         * character, it will reset the color to our default, because some UEFI implementations/terminals
+         * reset the color in that case, and we want our default color to remain in effect */
+
+        int32_t saved_attribute = ST->ConOut->Mode->Attribute;
+        for (;;) {
+                const char16_t *nl = strchr16(s, '\n');
+                if (!nl) /* No further newline */
+                        return (void) ST->ConOut->OutputString(ST->ConOut, (char16_t*) s);
+
+                if (nl[1] == 0) { /* Newline is at the end of the string */
+                        (void) ST->ConOut->OutputString(ST->ConOut, (char16_t*) s);
+                        set_attribute_safe(saved_attribute);
+                        return;
+                }
+
+                /* newline is in the middle of the string */
+                _cleanup_free_ char16_t *x = xstrndup16(s, nl - s + 1);
+                (void) ST->ConOut->OutputString(ST->ConOut, x);
+                set_attribute_safe(saved_attribute);
+
+                s = nl + 1;
+        }
+}
+#endif
+
 /* printf_internal is largely compatible to userspace vasprintf. Any features omitted should trigger asserts.
  *
  * Supported:
@@ -983,7 +1014,7 @@ _printf_(2, 0) static char16_t *printf_internal(EFI_STATUS status, const char *f
         }
 
 #if SD_BOOT
-        ST->ConOut->OutputString(ST->ConOut, ctx.buf);
+        output_string_safe(ST->ConOut, ctx.buf);
 #endif
 
         return mfree(ctx.dyn_buf);

src/boot/secure-boot.c

@@ -105,6 +105,9 @@ EFI_STATUS secure_boot_enroll_at(EFI_FILE *root_dir, const char16_t *path, bool
                                 timeout_sec--;
                                 continue;
                         }
+
+                        printf("\n");
+
                         if (err != EFI_SUCCESS)
                                 return log_error_status(
                                                 err,

src/boot/util.c

@@ -195,16 +195,27 @@ EFI_STATUS file_read(
         return file_handle_read(handle, offset, size, ret, ret_size);
 }
 
+void set_attribute_safe(size_t attr) {
+        /* Various UEFI implementations suppress color changes from a color to the same color. Often, we want
+         * to force out the color change though, hence change the color here once, and then back. We simply
+         * mark the color as bright for a moment, and then revert that. */
+
+        attr ^= 0x08;
+        ST->ConOut->SetAttribute(ST->ConOut, attr);
+        attr ^= 0x08;
+        ST->ConOut->SetAttribute(ST->ConOut, attr);
+}
+
 void print_at(size_t x, size_t y, size_t attr, const char16_t *str) {
         assert(str);
         ST->ConOut->SetCursorPosition(ST->ConOut, x, y);
-        ST->ConOut->SetAttribute(ST->ConOut, attr);
+        set_attribute_safe(attr);
         ST->ConOut->OutputString(ST->ConOut, (char16_t *) str);
 }
 
 void clear_screen(size_t attr) {
         log_wait();
-        ST->ConOut->SetAttribute(ST->ConOut, attr);
+        set_attribute_safe(attr);
         ST->ConOut->ClearScreen(ST->ConOut);
 }
 

src/boot/util.h

@@ -152,6 +152,7 @@ static inline void unload_imagep(EFI_HANDLE *image) {
 #define GUID_FORMAT_VAL(g) (g).Data1, (g).Data2, (g).Data3, (g).Data4[0], (g).Data4[1], \
         (g).Data4[2], (g).Data4[3], (g).Data4[4], (g).Data4[5], (g).Data4[6], (g).Data4[7]
 
+void set_attribute_safe(size_t attr);
 void print_at(size_t x, size_t y, size_t attr, const char16_t *str);
 void clear_screen(size_t attr);