Commit:     8c027ae2dcfa7b9130941a2a743c735c1fee04ee
Parent:     7ad37df02c529525c4ad19035359af89d2d2a5bd
Author:     H. Peter Anvin <[EMAIL PROTECTED]>
AuthorDate: Mon Jul 16 11:58:24 2007 -0700
Committer:  H. Peter Anvin <[EMAIL PROTECTED]>
CommitDate: Wed Jul 18 11:36:17 2007 -0700

    [x86 setup] Save/restore DS around invocations of INT 10h
    There exists at least one card, Trident TVGA8900CL (BIOS dated 1992/9/8)
    which clobbers DS when "scrolling in an SVGA text mode of more than
    800x600 pixels."  Although we are extremely unlikely to run into that
    situation, it is cheap insurance to save and restore DS, and it only adds
    a grand total of 50 bytes to the total output.
    Pointed out by Etienne Lorrain.
    Cc: Etienne Lorrain <[EMAIL PROTECTED]>
    Signed-off-by: H. Peter Anvin <[EMAIL PROTECTED]>
 arch/i386/boot/tty.c   |    2 +-
 arch/i386/boot/video.h |    9 ++++++++-
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/arch/i386/boot/tty.c b/arch/i386/boot/tty.c
index a8db787..9c668aa 100644
--- a/arch/i386/boot/tty.c
+++ b/arch/i386/boot/tty.c
@@ -31,7 +31,7 @@ void __attribute__((section(".inittext"))) putchar(int ch)
        /* int $0x10 is known to have bugs involving touching registers
           it shouldn't.  Be extra conservative... */
-       asm volatile("pushal; int $0x10; popal"
+       asm volatile("pushal; pushw %%ds; int $0x10; popw %%ds; popal"
                     : : "b" (0x0007), "c" (0x0001), "a" (0x0e00|ch));
diff --git a/arch/i386/boot/video.h b/arch/i386/boot/video.h
index 29eca17..b92447d 100644
--- a/arch/i386/boot/video.h
+++ b/arch/i386/boot/video.h
@@ -117,8 +117,15 @@ extern int graphic_mode;   /* Graphics mode with linear 
frame buffer */
  * int $0x10 is notorious for touching registers it shouldn't.
  * gcc doesn't like %ebp being clobbered, so define it as a push/pop
  * sequence here.
+ *
+ * A number of systems, including the original PC can clobber %bp in
+ * certain circumstances, like when scrolling.  There exists at least
+ * one Trident video card which could clobber DS under a set of
+ * circumstances that we are unlikely to encounter (scrolling when
+ * using an extended graphics mode of more than 800x600 pixels), but
+ * it's cheap insurance to deal with that here.
-#define INT10 "pushl %%ebp; int $0x10; popl %%ebp"
+#define INT10 "pushl %%ebp; pushw %%ds; int $0x10; popw %%ds; popl %%ebp"
 /* Accessing VGA indexed registers */
 static inline u8 in_idx(u16 port, u8 index)
To unsubscribe from this list: send the line "unsubscribe git-commits-head" in
the body of a message to [EMAIL PROTECTED]
More majordomo info at

Reply via email to