src/patches/suse-2.6.27.25/patches.fixes/video-vesa-bad-mode

   1 From: Michael Matz <matz@suse.de>
   2 Subject: x86/boot: fix clobbered register in vesa_store_edid
   3 References: bnc#400487
   4
   5 The only relevant difference that I can detect in the asm (comparing
   6 the output of gcc42-4.2.1_20070724-17.1 and gcc43-4.3.3_20081022-1.2) is
   7 in vesa_store_edid(), where the constant 0x4f15 is stored in a register
   8 which is reused in the second use after an int 0x10 call that could possibly
   9 clobber that register.
  10
  11 The asm certainly misses a clobber.  So, can you try adding one to this
  12 asm in vesa_store_edid:
  13
  14         /* Note: The VBE DDC spec is different from the main VESA spec;
  15            we genuinely have to assume all registers are destroyed here. */
  16         asm("pushw %%es; movw %2,%%es; "INT10"; popw %%es"
  17             : "+a" (ax), "+b" (bx)
  18             :  "c" (cx), "D" (di)
  19             : "esi");
  20
  21 In particular add "edx" to the clobber list (that's the register used
  22 in my case), but the above also misses "ecx", "edi", which have to be added
  23 as in/out constraints (i.e. "+c") probably, not as clobbers.
  24
  25 Note especially how the comment explicitely warns about assuming that
  26 all regs are destroyed, but how the asm makes no try to cater for that.
  27
  28 Tested-by: Andreas Schwab <schwab@suse.de>
  29 Acked-by: Jeff Mahoney <jeffm@suse.com>
  30 ---
  31
  32  arch/x86/boot/video-vesa.c |   12 +++++++-----
  33  1 file changed, 7 insertions(+), 5 deletions(-)
  34
  35 --- a/arch/x86/boot/video-vesa.c
  36 +++ b/arch/x86/boot/video-vesa.c
  37 @@ -270,9 +270,10 @@ void vesa_store_edid(void)
  38            we genuinely have to assume all registers are destroyed here. */
  39
  40         asm("pushw %%es; movw %2,%%es; "INT10"; popw %%es"
  41 -           : "+a" (ax), "+b" (bx)
  42 -           :  "c" (cx), "D" (di)
  43 -           : "esi");
  44 +           : "+a" (ax), "+b" (bx),
  45 +             "+c" (cx), "+D" (di)
  46 +           :
  47 +           : "esi", "edx");
  48
  49         if (ax != 0x004f)
  50                 return;         /* No EDID */
  51 @@ -286,8 +287,9 @@ void vesa_store_edid(void)
  52         dx = 0;                 /* EDID block number */
  53         di =(size_t) &boot_params.edid_info; /* (ES:)Pointer to block */
  54         asm(INT10
  55 -           : "+a" (ax), "+b" (bx), "+d" (dx), "=m" (boot_params.edid_info)
  56 -           : "c" (cx), "D" (di)
  57 +           : "+a" (ax), "+b" (bx), "+d" (dx), "=m" (boot_params.edid_info),
  58 +             "+c" (cx), "+D" (di)
  59 +           :
  60             : "esi");
  61  #endif /* CONFIG_FIRMWARE_EDID */
  62  }