[PATCH] arch/ppc/qemu: Moved exception handlers from beginning of RAM
Do not put exception handler routines between 0x00-0xff as some OSes use this area for their own purposes and can corrupt them. (In particular MorphOS writes to 0x80 during boot). This patch frees up this area by moving the routines that were there higher. Signed-off-by: BALATON Zoltan <balaton@eik.bme.hu> --- This replaces my previous attempt (Use exception vectors from ROM instead of copying them to page zero) as that relied on the MSR[IP] bit that was found not to be generally available. Index: openbios-devel/arch/ppc/qemu/start.S =================================================================== --- openbios-devel/arch/ppc/qemu/start.S (revision 1304) +++ openbios-devel/arch/ppc/qemu/start.S (working copy) @@ -280,21 +280,9 @@ GLOBL(__vectors): 1: nop // b 1b -call_dsi_exception: - LOAD_REG_FUNC(r3, dsi_exception) - mtctr r3 - bctrl - b exception_return +VECTOR( 0x100, "SRE" ): + b _entry -call_isi_exception: - LOAD_REG_FUNC(r3, isi_exception) - mtctr r3 - bctrl - b exception_return - -exception_return: - EXCEPTION_EPILOGUE - trap_error: lis r1, 0x8000 /* r1=0x80000000 */ add. r1,r1,r1 /* r1=r1+r1 (high 32bit !0) */ @@ -309,9 +297,6 @@ trap_error: mtctr r4 bctr -VECTOR( 0x100, "SRE" ): - b _entry - ILLEGAL_VECTOR( 0x200 ) VECTOR( 0x300, "DSI" ): @@ -373,11 +358,16 @@ VECTOR( 0x2200, "ISI_64" ): real_dsi: EXCEPTION_PREAMBLE - b call_dsi_exception + LOAD_REG_FUNC(r3, dsi_exception) + b call_exception_handler real_isi: EXCEPTION_PREAMBLE - b call_isi_exception + LOAD_REG_FUNC(r3, isi_exception) +call_exception_handler: + mtctr r3 + bctrl + EXCEPTION_EPILOGUE GLOBL(__vectors_end):
On 26.05.14 23:24, BALATON Zoltan wrote:
Do not put exception handler routines between 0x00-0xff as some OSes use this area for their own purposes and can corrupt them. (In particular MorphOS writes to 0x80 during boot). This patch frees up this area by moving the routines that were there higher.
Signed-off-by: BALATON Zoltan <balaton@eik.bme.hu>
So do you happen to have any idea why the code was written the way it was written? I don't feel very confident that I grasp why the original author did it that way. Alex
---
This replaces my previous attempt (Use exception vectors from ROM instead of copying them to page zero) as that relied on the MSR[IP] bit that was found not to be generally available.
Index: openbios-devel/arch/ppc/qemu/start.S =================================================================== --- openbios-devel/arch/ppc/qemu/start.S (revision 1304) +++ openbios-devel/arch/ppc/qemu/start.S (working copy) @@ -280,21 +280,9 @@ GLOBL(__vectors): 1: nop // b 1b
-call_dsi_exception: - LOAD_REG_FUNC(r3, dsi_exception) - mtctr r3 - bctrl - b exception_return +VECTOR( 0x100, "SRE" ): + b _entry
-call_isi_exception: - LOAD_REG_FUNC(r3, isi_exception) - mtctr r3 - bctrl - b exception_return - -exception_return: - EXCEPTION_EPILOGUE - trap_error: lis r1, 0x8000 /* r1=0x80000000 */ add. r1,r1,r1 /* r1=r1+r1 (high 32bit !0) */ @@ -309,9 +297,6 @@ trap_error: mtctr r4 bctr
-VECTOR( 0x100, "SRE" ): - b _entry - ILLEGAL_VECTOR( 0x200 )
VECTOR( 0x300, "DSI" ): @@ -373,11 +358,16 @@ VECTOR( 0x2200, "ISI_64" ):
real_dsi: EXCEPTION_PREAMBLE - b call_dsi_exception + LOAD_REG_FUNC(r3, dsi_exception) + b call_exception_handler
real_isi: EXCEPTION_PREAMBLE - b call_isi_exception + LOAD_REG_FUNC(r3, isi_exception) +call_exception_handler: + mtctr r3 + bctrl + EXCEPTION_EPILOGUE
GLOBL(__vectors_end):
On 28/05/14 00:59, Alexander Graf wrote:
On 26.05.14 23:24, BALATON Zoltan wrote:
Do not put exception handler routines between 0x00-0xff as some OSes use this area for their own purposes and can corrupt them. (In particular MorphOS writes to 0x80 during boot). This patch frees up this area by moving the routines that were there higher.
Signed-off-by: BALATON Zoltan <balaton@eik.bme.hu>
So do you happen to have any idea why the code was written the way it was written? I don't feel very confident that I grasp why the original author did it that way.
+1. ATB, Mark.
Le 28 mai 2014 à 10:02, Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk> a écrit :
On 28/05/14 00:59, Alexander Graf wrote:
On 26.05.14 23:24, BALATON Zoltan wrote:
Do not put exception handler routines between 0x00-0xff as some OSes use this area for their own purposes and can corrupt them. (In particular MorphOS writes to 0x80 during boot). This patch frees up this area by moving the routines that were there higher.
Signed-off-by: BALATON Zoltan <balaton@eik.bme.hu>
So do you happen to have any idea why the code was written the way it was written? I don't feel very confident that I grasp why the original author did it that way.
+1.
I think arch/ppc/qemu/start.S is coming from Mac-On-Linux. The MOL module is patching the host exception table to manage the virtual CPU. So I think this is the reason why it is written as it is. But Alexander I think you know better than me how MOL is working. Regards, Laurent
On Wed, 28 May 2014, Alexander Graf wrote:
So do you happen to have any idea why the code was written the way it was written? I don't feel very confident that I grasp why the original author did it that way.
No I don't have any idea why it looks like this but maybe only because previous changes wanted to preserve as much as possible (or change as little as possible) and they have added up like this. Looking at the commit logs I've found the following: - The exception_return part has been there from the beginning. - In r945 afaerber added call_[di]si_exception to free up 0x380 and 0x480 for illegal vectors. - The real_[di]si jumps has been added in r1043 by agraf probably because adding more instructions to the EXCEPTION_PREAMBLE made it not fit in 0x80 bytes any more. So I think you should now better as it seems you two are the original authors. Regards, BALATON Zoltan
Am 28.05.2014 12:05, schrieb BALATON Zoltan:
On Wed, 28 May 2014, Alexander Graf wrote:
So do you happen to have any idea why the code was written the way it was written? I don't feel very confident that I grasp why the original author did it that way.
No I don't have any idea why it looks like this but maybe only because previous changes wanted to preserve as much as possible (or change as little as possible) and they have added up like this. Looking at the commit logs I've found the following:
- The exception_return part has been there from the beginning.
- In r945 afaerber added call_[di]si_exception to free up 0x380 and 0x480 for illegal vectors.
AFAIR the issue was that the space in the exception table was insufficient so I needed to branch out somewhere. Another issue to keep in mind was that depending on QEMU's -cpu, OpenBIOS testing revealed that sometimes the exception code was called in place at fffffxxx and sometimes at the relocated addresses, so there were absolute vs. relative branches to consider. From the code relocated to 0x0 (or wherever that was) you need to do absolute jumps into the main OpenBIOS code, which require more instructions. Regards, Andreas
- The real_[di]si jumps has been added in r1043 by agraf probably because adding more instructions to the EXCEPTION_PREAMBLE made it not fit in 0x80 bytes any more.
So I think you should now better as it seems you two are the original authors.
Regards, BALATON Zoltan
-- SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg, Germany GF: Jeff Hawn, Jennifer Guild, Felix Imendörffer; HRB 16746 AG Nürnberg
On 26.05.14 23:24, BALATON Zoltan wrote:
Do not put exception handler routines between 0x00-0xff as some OSes use this area for their own purposes and can corrupt them. (In particular MorphOS writes to 0x80 during boot). This patch frees up this area by moving the routines that were there higher.
Signed-off-by: BALATON Zoltan <balaton@eik.bme.hu>
Please split this into 2 patches. One that only moves code from the call_xsi_exception into the real_xsi parts of the code. Then if you like do another patch on top that changes the calls to use call_exception_handler. The reason I'm asking for this is that there's quite some potential for breakage, and I would like to make sure we can easily find it through a bisect. Alex
---
This replaces my previous attempt (Use exception vectors from ROM instead of copying them to page zero) as that relied on the MSR[IP] bit that was found not to be generally available.
Index: openbios-devel/arch/ppc/qemu/start.S =================================================================== --- openbios-devel/arch/ppc/qemu/start.S (revision 1304) +++ openbios-devel/arch/ppc/qemu/start.S (working copy) @@ -280,21 +280,9 @@ GLOBL(__vectors): 1: nop // b 1b
-call_dsi_exception: - LOAD_REG_FUNC(r3, dsi_exception) - mtctr r3 - bctrl - b exception_return +VECTOR( 0x100, "SRE" ): + b _entry
-call_isi_exception: - LOAD_REG_FUNC(r3, isi_exception) - mtctr r3 - bctrl - b exception_return - -exception_return: - EXCEPTION_EPILOGUE - trap_error: lis r1, 0x8000 /* r1=0x80000000 */ add. r1,r1,r1 /* r1=r1+r1 (high 32bit !0) */ @@ -309,9 +297,6 @@ trap_error: mtctr r4 bctr
-VECTOR( 0x100, "SRE" ): - b _entry - ILLEGAL_VECTOR( 0x200 )
VECTOR( 0x300, "DSI" ): @@ -373,11 +358,16 @@ VECTOR( 0x2200, "ISI_64" ):
real_dsi: EXCEPTION_PREAMBLE - b call_dsi_exception + LOAD_REG_FUNC(r3, dsi_exception) + b call_exception_handler
real_isi: EXCEPTION_PREAMBLE - b call_isi_exception + LOAD_REG_FUNC(r3, isi_exception) +call_exception_handler: + mtctr r3 + bctrl + EXCEPTION_EPILOGUE
GLOBL(__vectors_end):
participants (5)
-
Alexander Graf -
Andreas Färber -
BALATON Zoltan -
Laurent Vivier -
Mark Cave-Ayland