[Qemu-devel] [PATCH] set vidmode in linux kernel header when boot x86 using qemu bootloader

[joy zhao <yanhwizhao@gmail.com>]

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hi,
I made a patch to have qemu parse vga field in kernel command line and set
the vid_mode field of real-mode kernel header.
This patch is necessary because vga is one of the special command line
options that should be parsed in bootloader, as in linux kernel
Documentation/x86/i386/boot.txt. After bootloader write the passed vga value
into the vid_mode field of linux real-mode kernel header, this vid_mode will
be handled by linux/x86/boot/video.c in linux kernel to select vesa graphics
mode, and only in this mode can vesafb be registered(in vesafb_probe()).
So, if we decide to launch linux directly from qemu command line as "qemu
-kernel ... -initrd... -append "..." ", (use qemu bootloader) and use vesafb
as framebuffer driver, this patch to qemu is required, otherwise, the screen
should just blank since the vesafb fails to register itself.
Joy.


diff --git a/qemu/hw/pc.c b/qemu-new/hw/pc.c
index 66cc780..5615db8 100644
--- a/qemu/hw/pc.c
+++ b/qemu-new/hw/pc.c
@@ -593,6 +593,77 @@ static long get_file_size(FILE *f)
     return size;
 }

+static uint16_t hato16i(char *hex)
+{
+ uint16_t integer = 0;
+ if(hex[1] == 'x')
+    hex += 2;
+
+    while(*hex != '\0'){
+  integer = (integer<<4);
+
+  if(*hex >= 0x30 && *hex <= 0x39){ /*0~9*/
+   integer += *hex - 0x30;
+  }else if(*hex >= 0x61 && *hex <= 0x66){ /*a~f*/
+   integer += *hex - 0x61 + 0xa;
+  }else if(*hex >= 0x41 && *hex <= 0x46){ /*A~F*/
+   integer += *hex - 0x41 + 0xa;
+  }else
+   break;
+
+  hex++;
+ }
+ return integer;
+}
+
+static uint16_t ato16i(char *dec)
+{
+ uint16_t integer = 0;
+
+    while(*dec != '\0'){
+  integer *= 10;
+
+  if(*dec >= 0x30 && *dec <= 0x39){ /*0~9*/
+   integer += *dec - 0x30;
+  }else
+   break;
+
+  dec++;
+ }
+ return integer;
+}
+
+static int get_vga_mode(const char* kernel_cmdline, uint16_t *vga_mode)
+{
+ char mode[6];
+ int i = 0;
+ char *p = strstr(kernel_cmdline, "vga=");
+ if(p == NULL)
+  return 1;
+
+ p += 4;
+
+ while(*p != ' ' && *p != '\0' && i < 6) {
+  mode[i] = *p;
+  i++;
+  p++;
+ }
+
+ if(!strncmp(mode, "ask", 3)){
+  *vga_mode = 0xfffd;
+ }else if(!strncmp(mode, "normal",6)){
+  *vga_mode = 0xffff;
+ }else if(!strncmp(mode, "ext", 3)){
+  *vga_mode = 0xfffe;
+ }else if(!strncmp(mode, "0x", 2)){//in hexdecimal
+  *vga_mode = hato16i(mode);
+ }else //in decimal
+  *vga_mode = ato16i(mode);
+
+ return 0;
+}
+
+
 static void load_linux(target_phys_addr_t option_rom,
                        const char *kernel_filename,
          const char *initrd_filename,
@@ -605,6 +676,7 @@ static void load_linux(target_phys_addr_t option_rom,
     uint16_t real_seg;
     int setup_size, kernel_size, initrd_size, cmdline_size;
     uint32_t initrd_max;
+ uint16_t vid_mode;
     uint8_t header[1024];
     target_phys_addr_t real_addr, prot_addr, cmdline_addr, initrd_addr;
     FILE *f, *fi;
@@ -683,6 +755,12 @@ static void load_linux(target_phys_addr_t option_rom,
     if (protocol >= 0x200)
  header[0x210] = 0xB0;

+ /*parse cmdline and set vga mode*/
+ if(!get_vga_mode(kernel_cmdline, &vid_mode)){
+  header[0x1fa] = vid_mode&0xff;
+  header[0x1fb] = (vid_mode&0xff00)>>8;
+ }
+
     /* heap */
     if (protocol >= 0x201) {
  header[0x211] |= 0x80; /* CAN_USE_HEAP */

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