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| author | Kevin O'Connor <kevin@koconnor.net> | 2014-11-05 09:05:36 -0500 |
|---|---|---|
| committer | Kevin O'Connor <kevin@koconnor.net> | 2014-11-12 12:17:57 -0500 |
| commit | aa66d6539cb11720477f2219a5821a9de1916384 (patch) | |
| tree | 5e0cd3c967b3096142c39bf105a3b34aa1a0dc04 /vgasrc/vgaentry.S | |
| parent | b4eb6fc5cc051e18d07f9483c093c9c32cece2f7 (diff) | |
| download | seabios-aa66d6539cb11720477f2219a5821a9de1916384.tar.gz | |
Use an aligned stack offset when entering on the extra stack
The size of 'struct bregs' is not evenly divisible by four and where
the assembler placed a 'struct bregs' on the extra stack as part of
entering into the C functions it caused the C functions to run with a
non-aligned stack. It's technically not correct to use an unaligned
stack and it is certainly less efficient.
This patch avoids using BREGS_size (the sizeof struct bregs) and
instead introduces PUSHBREGS_size (the size of the general purpose
registers in struct bregs) in the assembler. Where the code actually
did use the %cs:%ip and flags, an extra 8 (instead of 6) bytes are
added to maintain a sane alignment.
Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
Diffstat (limited to 'vgasrc/vgaentry.S')
| -rw-r--r-- | vgasrc/vgaentry.S | 20 |
1 files changed, 10 insertions, 10 deletions
diff --git a/vgasrc/vgaentry.S b/vgasrc/vgaentry.S index c05502d8..f9cf6568 100644 --- a/vgasrc/vgaentry.S +++ b/vgasrc/vgaentry.S @@ -112,10 +112,10 @@ entry_10_extrastack: pushw %ds // Set %ds:%eax to space on ExtraStack pushl %eax movw %cs:ExtraStackSeg, %ds - movl $(CONFIG_VGA_EXTRA_STACK_SIZE-BREGS_size-8), %eax + movl $(CONFIG_VGA_EXTRA_STACK_SIZE-PUSHBREGS_size-16), %eax SAVEBREGS_POP_DSEAX // Save registers on extra stack - movl %esp, BREGS_size+0(%eax) - movw %ss, BREGS_size+4(%eax) + movl %esp, PUSHBREGS_size+8(%eax) + movw %ss, PUSHBREGS_size+12(%eax) popl BREGS_code(%eax) popw BREGS_flags(%eax) @@ -125,8 +125,8 @@ entry_10_extrastack: VGA_CALLL handle_10 movl %esp, %eax // Restore registers and return - movw BREGS_size+4(%eax), %ss - movl BREGS_size+0(%eax), %esp + movw PUSHBREGS_size+12(%eax), %ss + movl PUSHBREGS_size+8(%eax), %esp popl %edx popw %dx pushw BREGS_flags(%eax) @@ -148,10 +148,10 @@ entry_timer_hook_extrastack: pushw %ds // Set %ds:%eax to space on ExtraStack pushl %eax movw %cs:ExtraStackSeg, %ds - movl $(CONFIG_VGA_EXTRA_STACK_SIZE-BREGS_size-8), %eax + movl $(CONFIG_VGA_EXTRA_STACK_SIZE-PUSHBREGS_size-8), %eax SAVEBREGS_POP_DSEAX - movl %esp, BREGS_size(%eax) - movw %ss, BREGS_size+4(%eax) + movl %esp, PUSHBREGS_size(%eax) + movw %ss, PUSHBREGS_size+4(%eax) movw %ds, %dx // Setup %ss/%esp and call function movw %dx, %ss @@ -159,7 +159,7 @@ entry_timer_hook_extrastack: calll handle_timer_hook movl %esp, %eax // Restore registers and return - movw BREGS_size+4(%eax), %ss - movl BREGS_size(%eax), %esp + movw PUSHBREGS_size+4(%eax), %ss + movl PUSHBREGS_size(%eax), %esp RESTOREBREGS_DSEAX ljmpw *%cs:Timer_Hook_Resume |