On 04/12/15 15:37, Ralf Baechle wrote:
On Fri, Dec 04, 2015 at 08:20:05AM +0000, Matt Redfearn wrote:
Although, it could still be reduced:
PTR_ADDU sp, gp, _THREAD_SIZE - 32 - PT_SIZE
Assuming the immediate is in range of signed 16bit.
The immediate would be 32552, so in range of signed 16bit, but that would be
brittle if either _THREAD_SIZE or PT_SIZE were to change in future....
The maximum value possible for _THREAD_SIZE would be with 64k pages for
which the expression will exceed the signed 16 bit range. The good news
is that GAS is smart enough to cope with the situation by suitably
expanding the instruction into a macro unless ".set noat" or ".set nomacro"
mode are enabled:
$ cat s.s
addu $sp, $gp, 65536
[ralf@h7 tmp]$ mips-linux-as -O2 -als -o s.o s.s
GAS LISTING s.s page 1
1 0000 3C010001 addu $sp, $gp, 65536
1 0381E821
1 00000000
1 00000000
GAS LISTING s.s page 2
NO DEFINED SYMBOLS
NO UNDEFINED SYMBOLS
[ralf@h7 tmp]$ mips-linux-objdump -d s.o
s.o: file format elf32-tradbigmips
Disassembly of section .text:
00000000 <.text>:
0: 3c010001 lui at,0x1
4: 0381e821 addu sp,gp,at
...
And of course that macro should better not be expanded in a branch
delay slot ...
Ralf
Cool, then it would be neater to do this (and perhaps the other instance
of this for setting the original kernel stack pointer up). Would you
prefer to see that in this series?
Thanks,
Matt
