From b015124e562a040f7faf361c72e8f5f457ac6cf5 Mon Sep 17 00:00:00 2001 From: "H. Peter Anvin" Date: Wed, 22 Aug 2007 16:28:01 -0700 Subject: [x86 setup] Volatilize asm() statements asm() statements need to be volatile when: a. They have side effects (other than value returned). b. When the value returned can vary over time. c. When they have ordering constraints that cannot be expressed to gcc. In particular, the keyboard and timer reads were violating constraint (b), which resulted in the keyboard/timeout poll getting loop-invariant-removed when compiling with gcc 4.2.0. Thanks to an anonymous bug reporter for pointing this out. Signed-off-by: H. Peter Anvin --- arch/i386/boot/video-vga.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) (limited to 'arch/i386/boot/video-vga.c') diff --git a/arch/i386/boot/video-vga.c b/arch/i386/boot/video-vga.c index 700d09a..d660e60 100644 --- a/arch/i386/boot/video-vga.c +++ b/arch/i386/boot/video-vga.c @@ -47,16 +47,16 @@ static u8 vga_set_basic_mode(void) #ifdef CONFIG_VIDEO_400_HACK if (adapter >= ADAPTER_VGA) { - asm(INT10 - : : "a" (0x1202), "b" (0x0030) - : "ecx", "edx", "esi", "edi"); + asm volatile(INT10 + : : "a" (0x1202), "b" (0x0030) + : "ecx", "edx", "esi", "edi"); } #endif ax = 0x0f00; - asm(INT10 - : "+a" (ax) - : : "ebx", "ecx", "edx", "esi", "edi"); + asm volatile(INT10 + : "+a" (ax) + : : "ebx", "ecx", "edx", "esi", "edi"); mode = (u8)ax; -- cgit v1.1 From 71351b98b9be6a867aa00276d67716c0728cfff7 Mon Sep 17 00:00:00 2001 From: "H. Peter Anvin" Date: Thu, 23 Aug 2007 09:28:42 -0700 Subject: [x86 setup] Make sure AH=00h when setting a video mode Passing a u8 into a register doesn't mean gcc will zero-extend it. Also, don't depend on thhe register not to change. Per bug report from Saul Tamari. Signed-off-by: H. Peter Anvin --- arch/i386/boot/video-vga.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) (limited to 'arch/i386/boot/video-vga.c') diff --git a/arch/i386/boot/video-vga.c b/arch/i386/boot/video-vga.c index d660e60..aef02f9 100644 --- a/arch/i386/boot/video-vga.c +++ b/arch/i386/boot/video-vga.c @@ -73,9 +73,10 @@ static u8 vga_set_basic_mode(void) mode = 3; /* Set the mode */ + ax = mode; asm volatile(INT10 - : : "a" (mode) - : "ebx", "ecx", "edx", "esi", "edi"); + : "+a" (ax) + : : "ebx", "ecx", "edx", "esi", "edi"); do_restore = 1; return mode; } -- cgit v1.1