[metal] Some minor fixes and tweaks (#933)

* [metal] Ensure DF is clear when calling C from exception handler
* [metal] Mark some internal routines and declarations as `@internal`
* [metal] Fix crash under UEFI when command line string is NULL
* [metal] Fix argc & argv[] setting, & VM page freeing, for UEFI

Part of the memory occupied by the argv[] contents was
erroneously used for page tables & then later erroneously
freed.  The symptom was that argv[0] would show up as an
empty string ("").

libc/vga/tty-graph.c

@@ -30,6 +30,7 @@
 #include "libc/vga/vga.internal.h"
 
 /**
+ * @internal
  * @fileoverview Instantiation of routines for normal console output in
  * graphical video modes.
  *

libc/vga/tty-graph.inc

@@ -31,6 +31,7 @@
 #include "libc/vga/vga.internal.h"
 
 /**
+ * @internal
  * @fileoverview Template for routines to support output in graphical video
  * modes for bare metal VGA.
  *

libc/vga/tty.greg.c

@@ -33,6 +33,7 @@
 #ifdef __x86_64__
 
 /**
+ * @internal
  * @fileoverview ECMA-48 / VT100 video terminal implementation for bare
  * metal VGA.
  *
@@ -325,6 +326,7 @@ static void TtySetCodepage(struct Tty *tty, char id) {
 }
 
 /**
+ * @internal
  * Map the given direct color value to one of the 16 basic foreground colors
  * or one of the 16 background colors.
  *
@@ -344,6 +346,7 @@ static uint8_t TtyGetTextColor(TtyCanvasColor color) {
 }
 
 /**
+ * @internal
  * Map the currently active foreground & background colors & terminal
  * configuration to a VGA text character attribute byte.
  *
@@ -794,12 +797,18 @@ static void TtyCsiN(struct Tty *tty) {
   }
 }
 
-/** Create a direct color pixel value. */
+/**
+ * @internal
+ * Create a direct color pixel value.
+ */
 static TtyCanvasColor TtyMapTrueColor(uint8_t r, uint8_t g, uint8_t b) {
   return (TtyCanvasColor){.bgr.r = r, .bgr.g = g, .bgr.b = b, .bgr.x = 0xff};
 }
 
-/** Map the given 256-color code to a direct color. */
+/**
+ * @internal
+ * Map the given 256-color code to a direct color.
+ */
 static TtyCanvasColor TtyMapXtermColor(uint8_t color) {
   uint8_t r, g, b;
   if (color < 8) {
@@ -822,7 +831,10 @@ static TtyCanvasColor TtyMapXtermColor(uint8_t color) {
   return TtyMapTrueColor(r, g, b);
 }
 
-/** Map the given ECMA-48 / VT100 SGR color code to a direct color. */
+/**
+ * @internal
+ * Map the given ECMA-48 / VT100 SGR color code to a direct color.
+ */
 static TtyCanvasColor TtyMapEcma48Color(uint8_t color) {
   return TtyMapXtermColor(color % 16);
 }

libc/vga/vga.internal.h

@@ -2,11 +2,20 @@
 #define COSMOPOLITAN_LIBC_VGA_VGA_INTERNAL_H_
 #include "libc/runtime/mman.internal.h"
 
-/** Preferred width of the video screen, in character units. */
+/**
+ * @internal
+ * Preferred width of the video screen, in character units.
+ */
 #define VGA_PREFER_TTY_HEIGHT 30
-/** Preferred width of the video screen, in character units. */
+/**
+ * @internal
+ * Preferred width of the video screen, in character units.
+ */
 #define VGA_PREFER_TTY_WIDTH 80
-/** Assumed height of each character in pixels, in graphics modes. */
+/**
+ * @internal
+ * Assumed height of each character in pixels, in graphics modes.
+ */
 #define VGA_ASSUME_CHAR_HEIGHT_PX 16
 /** Assumed width of each character in pixels, in graphics modes. */
 #define VGA_ASSUME_CHAR_WIDTH_PX 8
@@ -18,6 +27,7 @@
  */
 
 /**
+ * @internal
  * If VGA_USE_WCS is defined, the tty code can maintain an array of the
  * Unicode characters "underlying" the 8-bit (or 9-bit) characters that are
  * actually displayed on the text screen.  This Unicode character
@@ -33,6 +43,7 @@
  */
 #undef VGA_USE_WCS
 /**
+ * @internal
  * The VGA hardware can be configured — via the IBM BIOS, or via port I/O —
  * to either support blinking characters, or support the use of bright
  * background colors, but not both.  There is a hardware setting that
@@ -67,6 +78,7 @@
  */
 #undef VGA_USE_BLINK
 /**
+ * @internal
  * If VGA_PERSNICKETY_STATUS is defined, then when deciding how to return
  * status response codes (e.g. "\e[0n"), the tty code will pay attention to
  * the terminal's termios mode (TODO).  If undefined, the tty code will
@@ -75,7 +87,10 @@
  */
 #undef VGA_PERSNICKETY_STATUS
 
-/* Flags which are passed to _StartTty(). */
+/**
+ * @internal
+ * Flags which are passed to _StartTty().
+ */
 #define kTtyAllocWcs                       \
   0x01 /* allocate Unicode character array \
           (if VGA_USE_WCS also defined) */
@@ -85,6 +100,7 @@
           to show system messages */
 
 /**
+ * @internal
  * Flags for Tty::pr.  These govern properties of individual character cells.
  */
 #define kTtyFg      0x0001
@@ -102,6 +118,7 @@
 #define kTtyConceal 0x1000
 
 /**
+ * @internal
  * Flags for Tty::conf.  These govern the current state of the teletypewriter
  * as a whole.
  */
@@ -153,6 +170,10 @@ typedef union {
 typedef TtyBgrxColor TtyCanvasColor;
 struct Tty;
 
+/**
+ * @internal
+ * Video console object type.
+ */
 struct Tty {
   /**
    * Cursor position.  (y, x) = (0, 0) means the cursor is on the top left