[SeaBIOS] [PATCH] Use an aligned stack offset when entering on the extra stack
Kevin O'Connor
kevin at koconnor.net
Wed Nov 5 15:23:12 CET 2014
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 at koconnor.net>
---
src/asm-offsets.c | 1 -
src/entryfuncs.S | 2 ++
src/romlayout.S | 24 ++++++++++++------------
vgasrc/vgaentry.S | 20 ++++++++++----------
4 files changed, 24 insertions(+), 23 deletions(-)
diff --git a/src/asm-offsets.c b/src/asm-offsets.c
index 576bf34..b98f3b5 100644
--- a/src/asm-offsets.c
+++ b/src/asm-offsets.c
@@ -20,5 +20,4 @@ void foo(void)
OFFSET(BREGS_edi, bregs, edi);
OFFSET(BREGS_flags, bregs, flags);
OFFSET(BREGS_code, bregs, code);
- DEFINE(BREGS_size, sizeof(struct bregs));
}
diff --git a/src/entryfuncs.S b/src/entryfuncs.S
index cc1f433..7368bb6 100644
--- a/src/entryfuncs.S
+++ b/src/entryfuncs.S
@@ -9,6 +9,8 @@
* Macros for save and restore of 'struct bregs' registers
****************************************************************/
+#define PUSHBREGS_size 32
+
// Save registers (matches struct bregs) to stack
.macro PUSHBREGS
pushl %eax
diff --git a/src/romlayout.S b/src/romlayout.S
index 7a5df0e..c1751e1 100644
--- a/src/romlayout.S
+++ b/src/romlayout.S
@@ -257,7 +257,7 @@ entry_pmm:
movw %cx, %ds
shll $4, %ecx
movl $_cfunc32flat_handle_pmm, %eax // Setup: call32(handle_pmm, args, -1)
- leal BREGS_size-6+12(%esp, %ecx), %edx // %edx points to start of args
+ leal PUSHBREGS_size+12(%esp, %ecx), %edx // %edx points to start of args
movl $-1, %ecx
calll call32
movw %ax, BREGS_eax(%esp) // Modify %ax:%dx to return %eax
@@ -284,7 +284,7 @@ entry_pnp_real:
PUSHBREGS
movw %ss, %cx // Move %ss to %ds
movw %cx, %ds
- leal BREGS_size-6+12(%esp), %eax // %eax points to start of u16 args
+ leal PUSHBREGS_size+12(%esp), %eax // %eax points to start of u16 args
calll handle_pnp
movw %ax, BREGS_eax(%esp) // Modify %eax to return %ax
POPBREGS
@@ -433,11 +433,11 @@ irqentry_extrastack:
movl $_zonelow_seg, %eax
movl %eax, %ds
movl StackPos, %eax
- subl $BREGS_size+8, %eax
+ subl $PUSHBREGS_size+8, %eax
SAVEBREGS_POP_DSEAX
popl %ecx
- 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
@@ -445,8 +445,8 @@ irqentry_extrastack:
calll *%ecx
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
iretw
@@ -460,11 +460,11 @@ irqentry_arg_extrastack:
movl $_zonelow_seg, %eax
movl %eax, %ds
movl StackPos, %eax
- subl $BREGS_size+8, %eax
+ subl $PUSHBREGS_size+16, %eax
SAVEBREGS_POP_DSEAX // Save registers on extra stack
popl %ecx
- 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)
@@ -474,8 +474,8 @@ irqentry_arg_extrastack:
calll *%ecx
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)
diff --git a/vgasrc/vgaentry.S b/vgasrc/vgaentry.S
index c05502d..f9cf656 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
--
1.9.3
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