projects / ipfire-2.x.git / blame
| Commit | Line | Data |
|---|---|---|
| 00e5a55c BS |
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 | } |