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Version 1 (modified by jazz, 17 years ago) (diff)
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BUGFIX: jfbterm (1)

08-11-15@GMT-6 原紀錄 BUGFIX: jfbterm (1)

[DRBL] jfbterm Bug

https://bugs.launchpad.net/ubuntu/+source/jfbterm/+bug/253163
http://launchpadlibrarian.net/16414131/jfbterm-segfault.txt
http://launchpadlibrarian.net/16414135/jfbterm-segfault-strace.txt

[測試]

安裝 Ubuntu 8.10 Server AMD64

用 Ubuntu 8.10 的測試步驟:

root@intrepid:~# apt-get update
root@intrepid:~# apt-get upgrade
root@intrepid:~# reboot
root@intrepid:~# uname -a
Linux intrepid 2.6.27-7-server #1 SMP Tue Nov 4 20:16:57 UTC 2008 x86_64 GNU/Linux
root@intrepid:~# apt-get install jfbterm v86d
root@intrepid:~# reboot
root@intrepid:~# dpkg -S chvt
kbd: /usr/share/man/man1/chvt.1.gz
kbd: /bin/chvt
root@intrepid:~# chvt 1
root@intrepid:~# rmmod uvesafb
ERROR: Module uvesafb does not exist in /proc/modules
root@intrepid:~# modprobe uvesafb mode_option=1024x768
root@intrepid:~# screen
root@intrepid:~# jfbterm -e ls
... 略 ...
color 15 : ffff, ffff
cannot mmap(mmio) : Invalid argument
Segmentation fault

[備註] 如果沒有裝 v86d 的話，當執行 modprobe uvesafb 時會在 dmesg 看到以下資訊

[  703.839376] uvesafb: failed to execute /sbin/v86d
[  703.840224] uvesafb: make sure that the v86d helper is installed and executable
[  703.841494] uvesafb: Getting VBE info block failed (eax=0x4f00, err=-2)
[  703.842307] uvesafb: vbe_init() failed with -22
[  703.843019] uvesafb: probe of uvesafb.0 failed with error -22

[備註] 如果有裝 v86d 的話，當執行 modprobe uvesafb 時會在 dmesg 看到以下資訊

[  268.848377] uvesafb: VMware, IncVMware virtual machine2.0, VMware virtual machine2.0, 2.0, OEM: V M ware, Inc. VBE support 2.0VMware, IncVMware virtual machine2.0, VBE v2.0
[  268.884099] uvesafb: no monitor limits have been set, default refresh rate will be used
[  268.885202] uvesafb: VBE state buffer size cannot be determined (eax=0x0, err=0)
[  268.885265] uvesafb: scrolling: redraw
[  268.896617] mtrr: your processor doesn't support write-combining
[  268.909303] Console: switching to colour frame buffer device 128x48
[  269.938085] uvesafb: framebuffer at 0xf0000000, mapped to 0xffffc20000180000, using 16384k, total 16384k
[  269.938101] fb0: VESA VGA frame buffer device

Ubuntu 8.10 Kernel 2.6.27-7-server 的 uvesafb 參數包括 scroll、vgapal、pmipal、mtrr、blank、nocrtc、noedid、vram_remap、vram_total、maxclk、maxhf、maxvf、mode_option、vbemode、v86d。

root@intrepid:~# modinfo uvesafb
filename:       /lib/modules/2.6.27-7-server/kernel/drivers/video/uvesafb.ko
description:    Framebuffer driver for VBE2.0+ compliant graphics boards
author:         Michal Januszewski <spock@gentoo.org>
license:        GPL
srcversion:     21EDEFDED06E0673208A0D5
depends:
vermagic:       2.6.27-7-server SMP mod_unload modversions
parm:           scroll:Scrolling mode, set to 'redraw', 'ypan', or 'ywrap' (scroll)
parm:           vgapal:Set palette using VGA registers (invbool)
parm:           pmipal:Set palette using PMI calls (bool)
parm:           mtrr:Memory Type Range Registers setting. Use 0 to disable. (uint)
parm:           blank:Enable hardware blanking (bool)
parm:           nocrtc:Ignore CRTC timings when setting modes (bool)
parm:           noedid:Ignore EDID-provided monitor limits when setting modes (bool)
parm:           vram_remap:Set amount of video memory to be used [MiB] (uint)
parm:           vram_total:Set total amount of video memoery [MiB] (uint)
parm:           maxclk:Maximum pixelclock [MHz], overrides EDID data (ushort)
parm:           maxhf:Maximum horizontal frequency [kHz], overrides EDID data (ushort)
parm:           maxvf:Maximum vertical frequency [Hz], overrides EDID data (ushort)
parm:           mode_option:Specify initial video mode as "<xres>x<yres>[-<bpp>][@<refresh>]" (charp)
parm:           vbemode:VBE mode number to set, overrides the 'mode' option (ushort)
parm:           v86d:Path to the v86d userspace helper. (string)

root@intrepid:~# LANG=C apt-cache policy v86d
v86d:
  Installed: 0.1.5-1ubuntu2
  Candidate: 0.1.5-1ubuntu2
  Version table:
 *** 0.1.5-1ubuntu2 0
        500 http://tw.archive.ubuntu.com intrepid/universe Packages
        100 /var/lib/dpkg/status

root@intrepid:~# LANG=C apt-cache policy jfbterm
jfbterm:
  Installed: 0.4.7-7.2
  Candidate: 0.4.7-7.2
  Version table:
 *** 0.4.7-7.2 0
        500 http://tw.archive.ubuntu.com intrepid/universe Packages
        100 /var/lib/dpkg/status

追蹤 jfbterm 的 deb package 原始碼

root@intrepid:~# apt-get build-dep jfbterm
root@intrepid:~# apt-get install dpkg-dev
root@intrepid:~# apt-get source jfbterm

uvesafb 作者的推測:

As to why the console becomes unresponsive after exiting jfbterm --
jfbterm sets KD_GRAPHICS mode on the console on which it is started,
and apparently fails to set it back to KD_TEXT before segfaulting.  This
leaves the console in the broken state.

尋找合理懷疑對象:

root@intrepid:~/jfbterm-0.4.7# grep "KD_GRAPHICS" *
vterm.c:        ioctl(0, KDSETMODE, KD_GRAPHICS);

root@intrepid:~/jfbterm-0.4.7# grep "KD_TEXT" *
main.c:        if (mode == KD_TEXT) {
vterm.c:        ioctl(0, KDSETMODE, KD_TEXT);

BUGFIX: jfbterm (2)

08-11-16@GMT-6 原紀錄 BUGFIX: jfbterm (2)

尋找合理懷疑對象:

root@intrepid:~/jfbterm-0.4.7# grep "KD_GRAPHICS" *
vterm.c:        ioctl(0, KDSETMODE, KD_GRAPHICS);

root@intrepid:~/jfbterm-0.4.7# grep "KD_TEXT" *
main.c:        if (mode == KD_TEXT) {
vterm.c:        ioctl(0, KDSETMODE, KD_TEXT);

root@intrepid:~/jfbterm-0.4.7# grep "cannot mmap" *
fbcommon.c:             die("cannot mmap(smem)");
fbcommon.c:             die("cannot mmap(mmio)");
fbcommon.c:             print_message("cannot mmap(mmio) : %s\n", strerror(errno));

啟用 DEBUG 旗標，編譯 jfbterm，使用 gdb 追蹤

root@intrepid:~/jfbterm-0.4.7# ./configure --enable-debug
root@intrepid:~/jfbterm-0.4.7# make
root@intrepid:~/jfbterm-0.4.7# gdb ./jfbterm
(gdb) run

縱使用 gdb 還是無法正常跳回文字模式，因此直接追原始碼。

根據錯誤訊息,應該是錯在 fbcommon.c 的第 572 行，往前追造成錯誤的原因是 566 行的 mmap()，歸屬在 tfbm_open() 函數

< fbcommon.c >

482 void tfbm_open(TFrameBufferMemory* p)

566         p->mmio = (u_char*)mmap(NULL, p->mlen, PROT_READ|PROT_WRITE,
567                                 MAP_SHARED, p->fh, p->slen);
568         if ((long)p->mmio == -1) {
569 #ifdef JFB_MMIO_CHECK
570                 die("cannot mmap(mmio)");
571 #else
572                 print_message("cannot mmap(mmio) : %s\n", strerror(errno));
573 #endif

< main.c >

368 int main(int argc, char *argv[])
431         tfbm_open(&gFramebuffer);

安裝 manpages-dev 套件，查 mmap 、 strerror 跟 errno 的 manpage。從 cannot mmap(mmio) : Invalid argument 這個錯誤訊息可以判斷 errno 等於 EINVAL。而 mmap 發生 EINVAL 的情形有三種，最可能的原因是第一個：We don't like addr, length, or offset (e.g., they are too large, or not aligned on a page boundary).

這裡注意到 mmap 的 offset 參數必須是 sysconf 中定義 _SC_PAGE_SIZE 的倍數。(offset must be a multiple of the page size as returned by sysconf(_SC_PAGE_SIZE).)

root@intrepid:~/jfbterm-0.4.7# apt-get install manpages-dev

root@intrepid:~/jfbterm-0.4.7# man errno

       EINVAL          Invalid argument (POSIX.1)

void *mmap(void *addr, size_t length, int prot, int flags, int fd, off_t offset);

offset must be a multiple of the page size as returned by sysconf(_SC_PAGE_SIZE).

ERRORS
       EINVAL We don't like addr, length, or offset (e.g., they are too large, or not aligned on a page boundary).
       EINVAL (since Linux 2.6.12) length was 0.
       EINVAL flags contained neither MAP_PRIVATE or MAP_SHARED, or contained both of these values.

使用 gdb 設定中斷點在 fbcomm.c 第 566 行並觀察變數狀態

root@intrepid:~/jfbterm-0.4.7# gdb
(gdb) file jfbterm
Reading symbols from /root/jfbterm-0.4.7/jfbterm...done.
(gdb) set args -e ls
(gdb) show args
Argument list to give program being debugged when it is started is "-e ls".
(gdb) break fbcommon.c:566
Breakpoint 1 at 0x4034ba: file fbcommon.c, line 566.
(gdb) run
... 略 ...
Breakpoint 1, tfbm_open (p=0x6146e0) at fbcommon.c:566
566             p->mmio = (u_char*)mmap(NULL, p->mlen, PROT_READ|PROT_WRITE,
(gdb) l
561             }
562             p->smem = (char *)p->smem + p->soff;
563
564             p->moff = (u_long)(fb_fix.mmio_start) & (~PAGE_MASK);
565             p->mlen = (fb_fix.mmio_len + p->moff + ~PAGE_MASK) & PAGE_MASK;
566             p->mmio = (u_char*)mmap(NULL, p->mlen, PROT_READ|PROT_WRITE,
567                                     MAP_SHARED, p->fh, p->slen);
568             if ((long)p->mmio == -1) {
569     #ifdef JFB_MMIO_CHECK
570                     die("cannot mmap(mmio)");
(gdb) p fb_fix.mmio_len
$1 = 0
(gdb) p p->moff
$2 = 0
(gdb) p p->mlen
$3 = 0
(gdb) p p->fh
$4 = 6
(gdb) p p->slen
$5 = 1572864
(gdb) p fb_fix.smem_len
$6 = 1572864

BUGFIX: jfbterm (3)

08-11-17@GMT-6 原紀錄 BUGFIX: jfbterm (3)

編輯 GRUB 的 menu.lst 就可以不用每次都跑 modprobe

menu.lst

-                      old
+                      new
 title          Ubuntu 8.10, kernel 2.6.27-7-server
 uuid           574912ac-8bd6-4cc7-90c6-8c5362033fec
 kernel         /boot/vmlinuz-2.6.27-7-server root=UUID=574912ac-8bd6-4cc7-90c6-8c5362033fec ro quiet splash
+kernel         /boot/vmlinuz-2.6.27-7-server root=UUID=574912ac-8bd6-4cc7-90c6-8c5362033fec ro quiet splash vga=0x305
 initrd         /boot/initrd.img-2.6.27-7-server
 quiet

mmap 的 offset 參數必須是 sysconf 中定義 _SC_PAGE_SIZE 的倍數。(offset must be a multiple of the page size as returned by sysconf(_SC_PAGE_SIZE).)
使用 gdb 設定中斷點在 fbcomm.c 第 566 行並觀察變數狀態，可以知道送到 mmap 函數的 offset 參數內容為 1572864 。
```
(gdb) p p->slen
$5 = 1572864
```

為了確認 offset 參數是否為 _SC_PAGESIZE 的整數倍，先撰寫測試程式，用 sysconf 取得目前系統的 _SC_PAGESIZE 屬性。

root@intrepid:~# cat > get_sc_pagesize.c << EOF
#include <unistd.h>
#include <stdio.h>

int main()
{
  printf("_SC_PAGESIZE = %ld\n",sysconf(_SC_PAGESIZE));
}
EOF
root@intrepid:~# gcc get_sc_pagesize.c -o get_sc_pagesize
root@intrepid:~# ./get_sc_pagesize
_SC_PAGESIZE = 4096

根據 mmap 的 manpages，產生 EINVAL 錯誤的另一個原因是 length 等於零(從 Linux 2.6.12 以後)，確認主因為 length 參數 = p->mlen = 0

MMAP(2): void *mmap(void *addr, size_t length, int prot, int flags, int fd, off_t offset);
MMAP(2): EINVAL (since Linux 2.6.12) length was 0.

566             p->mmio = (u_char*)mmap(NULL, p->mlen, PROT_READ|PROT_WRITE,
567                                     MAP_SHARED, p->fh, p->slen);
(gdb) p p->mlen
$3 = 0

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