I just discovered that my compiler is scheduling the code in the asm
blocks in unaligned.c *before* the 'goto sigbus'. My gcc is 3.1.1 with
some almost certainly unrelated local mods.
Anyway, is there a reason these aren't marked as volatile? The gcc docs
have the scary comment "You can prevent an `asm' instruction from being
deleted, MOVED SIGNIFICANTLY, or combined, by writing the keyword
`volatile' after the`asm'."
Here's an example, for the lw_op case in the mips64 kernel:
---------
case lw_op:
if (verify_area(VERIFY_READ, addr, 4))
goto sigbus;
__asm__(
"1:\tlwl\t%0, (%2)\n"
"2:\tlwr\t%0, 3(%2)\n\t"
---------
Compiled with normal mips64 build flags (for SB1) was turned into:
---------
### verify_area
ld $2,2400($28)
daddu $3,$5,4
or $3,$5,$3
and $2,$2,$3
li $4,-14 # 0xfffffffffffffff2
movz $4,$0,$2
...
### the asm code
1: lwl $9, ($5)
2: lwr $9, 3($5)
li $3, 0
3: .section .fixup,"ax"
4: li $3, -14
j 3b
...
### finally, the verify_area result check
beq $4,$0,$L1131
---------
Kip
