Kernel build parameter CONFIG_REGPARAM breaks binary modules

[Earle Nietzel]

I've noticed since moving to 2.6.x that none of my binary modules would
load correctly.

After reading that CONFIG_REGPARAM was the culprit I disabled it but to
my surprise nothing changed.

Come to find out that in "arch/i386/Makefile":

CFLAGS += -pipe -mregparm=3 -msoft-float -fno-builtin-sprintf -fno-
builtin-log2 -fno-builtin-puts

You'll notice "-mregparm=3"?

After removing this compiler flag my binary modules began to load
correctly.

Anyone care to comment on this?


Earle Nietzel




Here is what the kernel oops looks like with with "-mregparm=3":

Unable to handle kernel paging request at virtual address e0a18ab4
 printing eip:
e0a64a58
*pde = 170fc2a5
Oops: 0000 [#1]
CPU:    1
EIP:    0060:[<e0a64a58>]    Tainted: PF
EFLAGS: 00010246
EIP is at firegl_init+0x40/0xf6 [fglrx]
eax: e0a891e0   ebx: e0a18ab4   ecx: 00000002   edx: dead4ead
esi: e0a893a0   edi: e0a89210   ebp: c033ebb8   esp: def79f58
ds: 007b   es: 007b   ss: 0068
Process modprobe (pid: 761, threadinfo=def78000 task=df166000)
Stack: 00000012 00000000 00000000 e0a891e0 e0a88980 e0a891e0 e0a88980
e0807280
       e0a18ab4 00000246 09289088 00000000 c032e618 b7e77008 c033ebd8
c033ebd8
       c033ebb8 c01450a6 c016bc7c df505578 df5055a0 00000000 b7e77008
bff73658
Call Trace:
 [<e0807280>] firegl_init_module+0x110/0x1b0 [fglrx]
 [<c01450a6>] sys_init_module+0x136/0x290
 [<c016bc7c>] sys_close+0x7c/0xf0
 [<c010bc3f>] syscall_call+0x7/0xb
 
Code: 81 3b 00 00 02 10 74 11 c7 44 24 04 03 7b a7 e0 c7 04 24 40

[Dave Jones]

On Tue, 2004-03-16 at 23:47, Earle Robert Nietzel wrote:
>  I've noticed since moving to 2.6.x that none of my binary modules
> would
>  load correctly.
>  
>  After reading that CONFIG_REGPARAM was the culprit I disabled it but to
>  my surprise nothing changed.
>  
>  Come to find out that in "arch/i386/Makefile":
>  
>  CFLAGS += -pipe -mregparm=3 -msoft-float -fno-builtin-sprintf -fno-
>  builtin-log2 -fno-builtin-puts
>  
>  You'll notice "-mregparm=3"?
>  
>  After removing this compiler flag my binary modules began to load
>  correctly.
>  
>  Anyone care to comment on this? 
A leftover from the days before CONFIG_REGPARM existed.
I've killed it in cvs.

	Dave

[Alan Cox]

On Wed, Mar 17, 2004 at 12:47:13AM +0100, Earle Robert Nietzel wrote:
>  Come to find out that in "arch/i386/Makefile":
>  
>  CFLAGS += -pipe -mregparm=3 -msoft-float -fno-builtin-sprintf -fno-
>  builtin-log2 -fno-builtin-puts
>  
>  You'll notice "-mregparm=3"?
>  
>  After removing this compiler flag my binary modules began to load
>  correctly.
>  
>  Anyone care to comment on this? 
Your binary modules need to match the kernel. -mregparm=3 tells the
kernel to try and use registers for some of the argument passing, and
thus be more efficient

[Earle Nietzel]

On Wed, 2004-03-17 at 09:38 -0500, Alan Cox wrote:
>  On Wed, Mar 17, 2004 at 12:47:13AM +0100, Earle Robert Nietzel
> wrote:
>  > Come to find out that in "arch/i386/Makefile":
>  > 
>  > CFLAGS += -pipe -mregparm=3 -msoft-float -fno-builtin-sprintf -fno-
>  > builtin-log2 -fno-builtin-puts
>  > 
>  > You'll notice "-mregparm=3"?
>  > 
>  > After removing this compiler flag my binary modules began to load
>  > correctly.
>  > 
>  > Anyone care to comment on this?
>  
>  Your binary modules need to match the kernel. -mregparm=3 tells the
>  kernel to try and use registers for some of the argument passing, and
>  thus be more efficient 
I patched the ATI fglrx driver so that it compiles with -mregparm=3 and
the performance difference is noticably faster. 

I understand the reason for using fastcalls but could you explain the
syntax implementation?

For example I know GCC uses a __attribute__((cdecl)) but the actual
details behind this are not obvious to me.

Thanks for your time and patience!

[Alan Cox]

On Thu, Mar 18, 2004 at 12:34:36AM +0100, Earle Robert Nietzel wrote:
>  I patched the ATI fglrx driver so that it compiles with -mregparm=3
> and
>  the performance difference is noticably faster. 
>  
>  I understand the reason for using fastcalls but could you explain the
>  syntax implementation?
>  
>  For example I know GCC uses a __attribute__((cdecl)) but the actual
>  details behind this are not obvious to me. 
You want to be able to use regcalls but also specify some functions
(for example functions in other languages, libraries or asm blocks)
should be called using the traditional syntax