The branch main has been updated by tsoome:

URL: 
https://cgit.FreeBSD.org/src/commit/?id=ad1ebbe5cea8ffac0037966990ddf0f80faa55d5

commit ad1ebbe5cea8ffac0037966990ddf0f80faa55d5
Author:     Toomas Soome <tso...@freebsd.org>
AuthorDate: 2021-01-16 10:18:32 +0000
Commit:     Toomas Soome <tso...@freebsd.org>
CommitDate: 2021-01-16 10:23:22 +0000

    loader: create local copy of mode list provided by vbeinfoblock
    
    Apparently some systems do corrupt mode list memory area, so we need
    to use local copy instead.
---
 stand/i386/libi386/vbe.c | 82 +++++++++++++++++++++++++++++-------------------
 1 file changed, 49 insertions(+), 33 deletions(-)

diff --git a/stand/i386/libi386/vbe.c b/stand/i386/libi386/vbe.c
index 6a70cfe6f3e9..8b2c74ade92e 100644
--- a/stand/i386/libi386/vbe.c
+++ b/stand/i386/libi386/vbe.c
@@ -48,12 +48,14 @@
 
 static struct vbeinfoblock *vbe;
 static struct modeinfoblock *vbe_mode;
+
+static uint16_t *vbe_mode_list;
+static size_t vbe_mode_list_size;
+
 /* The default VGA color palette format is 6 bits per primary color. */
 int palette_format = 6;
 
 #define        VESA_MODE_BASE  0x100
-#define        VESA_MODE_MAX   0x1ff
-#define        VESA_MODE_COUNT (VESA_MODE_MAX - VESA_MODE_BASE + 1)
 
 /*
  * palette array for 8-bit indexed colors. In this case, cmap does store
@@ -545,9 +547,17 @@ mode_set(struct env_var *ev, int flags __unused, const 
void *value)
        return (0);
 }
 
+static void *
+vbe_farptr(uint32_t farptr)
+{
+       return (PTOV((((farptr & 0xffff0000) >> 12) + (farptr & 0xffff))));
+}
+
 void
 vbe_init(void)
 {
+       uint16_t *p, *ml;
+
        /* First set FB for text mode. */
        gfx_state.tg_fb_type = FB_TEXT;
        gfx_state.tg_fb.fb_height = TEXT_ROWS;
@@ -573,6 +583,27 @@ vbe_init(void)
                vbe_mode = NULL;
        }
 
+       /*
+        * Copy mode list. We must do this because some systems do
+        * corrupt the provided list (vbox 6.1 is one example).
+        */
+       p = ml = vbe_farptr(vbe->VideoModePtr);
+       while(*p++ != 0xFFFF)
+               ;
+
+       vbe_mode_list_size = (uintptr_t)p - (uintptr_t)ml;
+       vbe_mode_list = malloc(vbe_mode_list_size);
+       if (vbe_mode_list == NULL) {
+               free(vbe);
+               vbe = NULL;
+               free(vbe_mode);
+               vbe_mode = NULL;
+       }
+       bcopy(ml, vbe_mode_list, vbe_mode_list_size);
+
+       /* reset VideoModePtr, so we will not have chance to use bad data. */
+       vbe->VideoModePtr = 0;
+
        env_setenv("screen.textmode", EV_VOLATILE, "1", mode_set,
            env_nounset);
        env_setenv("vbe_max_resolution", EV_VOLATILE, NULL, mode_set,
@@ -717,12 +748,6 @@ vbe_set_mode(int modenum)
        return (0);
 }
 
-static void *
-vbe_farptr(uint32_t farptr)
-{
-       return (PTOV((((farptr & 0xffff0000) >> 12) + (farptr & 0xffff))));
-}
-
 /*
  * Verify existance of mode number or find mode by
  * dimensions. If depth is not given, walk values 32, 24, 16, 8.
@@ -731,15 +756,13 @@ static int
 vbe_find_mode_xydm(int x, int y, int depth, int m)
 {
        struct modeinfoblock mi;
-       uint32_t farptr;
+       uint16_t *farptr;
        uint16_t mode;
-       int safety, i;
+       int idx, nitems, i;
 
        memset(vbe, 0, sizeof (*vbe));
        if (biosvbe_info(vbe) != VBE_SUCCESS)
                return (0);
-       if (vbe->VideoModePtr == 0)
-               return (0);
 
        if (m != -1)
                i = 8;
@@ -748,17 +771,17 @@ vbe_find_mode_xydm(int x, int y, int depth, int m)
        else
                i = depth;
 
+       nitems = vbe_mode_list_size / sizeof(*vbe_mode_list);
        while (i > 0) {
-               farptr = vbe->VideoModePtr;
-               safety = 0;
-               while ((mode = *(uint16_t *)vbe_farptr(farptr)) != 0xffff) {
-                       safety++;
-                       farptr += 2;
-                       if (safety == VESA_MODE_COUNT)
+               for (idx = 0; idx < nitems; idx++) {
+                       mode = vbe_mode_list[idx];
+                       if (mode == 0xffff)
                                break;
+
                        if (biosvbe_get_mode_info(mode, &mi) != VBE_SUCCESS) {
                                continue;
                        }
+
                        /* we only care about linear modes here */
                        if (vbe_mode_is_supported(&mi) == 0)
                                continue;
@@ -910,9 +933,8 @@ void
 vbe_modelist(int depth)
 {
        struct modeinfoblock mi;
-       uint32_t farptr;
        uint16_t mode;
-       int nmodes = 0, safety = 0;
+       int nmodes, idx, nentries;
        int ddc_caps;
        uint32_t width, height;
        bool edid = false;
@@ -948,6 +970,7 @@ vbe_modelist(int depth)
                if (vbe_get_flatpanel(&width, &height))
                        printf(": Panel %dx%d\n", width, height);
 
+       nmodes = 0;
        memset(vbe, 0, sizeof (*vbe));
        memcpy(vbe->VbeSignature, "VBE2", 4);
        if (biosvbe_info(vbe) != VBE_SUCCESS)
@@ -958,26 +981,19 @@ vbe_modelist(int depth)
        vbe_print_vbe_info(vbe);
        printf("Modes: ");
 
-       farptr = vbe->VideoModePtr;
-       if (farptr == 0)
-               goto done;
-
-       while ((mode = *(uint16_t *)vbe_farptr(farptr)) != 0xffff) {
-               safety++;
-               farptr += 2;
-               if (safety == VESA_MODE_COUNT) {
-                       printf("[?] ");
+       nentries = vbe_mode_list_size / sizeof(*vbe_mode_list);
+       for (idx = 0; idx < nentries; idx++) {
+               mode = vbe_mode_list[idx];
+               if (mode == 0xffff)
                        break;
-               }
+
                if (biosvbe_get_mode_info(mode, &mi) != VBE_SUCCESS)
                        continue;
+
                /* we only care about linear modes here */
                if (vbe_mode_is_supported(&mi) == 0)
                        continue;
 
-               /* we found some mode so reset safety counter */
-               safety = 0;
-
                /* apply requested filter */
                if (depth != -1 && mi.BitsPerPixel != depth)
                        continue;
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