* [Qemu-devel] [PATCH v2] linux-user: ppc64: don't use volatile register during safe_syscall
@ 2018-07-26 8:26 Shivaprasad G Bhat
2018-07-27 3:13 ` [Qemu-devel] [Qemu-ppc] " David Gibson
0 siblings, 1 reply; 4+ messages in thread
From: Shivaprasad G Bhat @ 2018-07-26 8:26 UTC (permalink / raw)
To: dgibson, riku.voipio, richard.henderson, laurent
Cc: qemu-ppc, sbhat, qemu-devel
r11 is a volatile register on PPC as per calling conventions.
The safe_syscall code uses it to check if the signal_pending
is set during the safe_syscall. When a syscall is interrupted
on return from signal handling, the r11 might be corrupted
before we retry the syscall leading to a crash. The registers
r0-r13 are not to be used here as they have
volatile/designated/reserved usages. Change the code to use
r14 which is non-volatile and is appropriate for local use in
safe_syscall.
Steps to reproduce:
On PPC host, issue `qemu-x86_64 /usr/bin/cc -E -`
Attempt Ctrl-C, the issue is reproduced.
Reference:
https://refspecs.linuxfoundation.org/ELF/ppc64/PPC-elf64abi-1.9.html#REG
Signed-off-by: Shivaprasad G Bhat <sbhat@linux.vnet.ibm.com>
Tested-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
---
v1: https://lists.gnu.org/archive/html/qemu-devel/2018-07/msg05089.html
Changes from v1:
Fixed the commit message as suggested
linux-user/host/ppc64/safe-syscall.inc.S | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/linux-user/host/ppc64/safe-syscall.inc.S b/linux-user/host/ppc64/safe-syscall.inc.S
index d30050a67c..b0cbbe6a69 100644
--- a/linux-user/host/ppc64/safe-syscall.inc.S
+++ b/linux-user/host/ppc64/safe-syscall.inc.S
@@ -49,7 +49,7 @@ safe_syscall_base:
* and returns the result in r3
* Shuffle everything around appropriately.
*/
- mr 11, 3 /* signal_pending */
+ mr 14, 3 /* signal_pending */
mr 0, 4 /* syscall number */
mr 3, 5 /* syscall arguments */
mr 4, 6
@@ -67,7 +67,7 @@ safe_syscall_base:
*/
safe_syscall_start:
/* if signal_pending is non-zero, don't do the call */
- lwz 12, 0(11)
+ lwz 12, 0(14)
cmpwi 0, 12, 0
bne- 0f
sc
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [Qemu-devel] [Qemu-ppc] [PATCH v2] linux-user: ppc64: don't use volatile register during safe_syscall
2018-07-26 8:26 [Qemu-devel] [PATCH v2] linux-user: ppc64: don't use volatile register during safe_syscall Shivaprasad G Bhat
@ 2018-07-27 3:13 ` David Gibson
2018-07-27 5:20 ` Richard Henderson
0 siblings, 1 reply; 4+ messages in thread
From: David Gibson @ 2018-07-27 3:13 UTC (permalink / raw)
To: Shivaprasad G Bhat
Cc: dgibson, riku.voipio, richard.henderson, laurent, qemu-ppc,
qemu-devel
[-- Attachment #1: Type: text/plain, Size: 2218 bytes --]
On Thu, Jul 26, 2018 at 01:56:19PM +0530, Shivaprasad G Bhat wrote:
> r11 is a volatile register on PPC as per calling conventions.
> The safe_syscall code uses it to check if the signal_pending
> is set during the safe_syscall. When a syscall is interrupted
> on return from signal handling, the r11 might be corrupted
> before we retry the syscall leading to a crash. The registers
> r0-r13 are not to be used here as they have
> volatile/designated/reserved usages. Change the code to use
> r14 which is non-volatile and is appropriate for local use in
> safe_syscall.
>
> Steps to reproduce:
> On PPC host, issue `qemu-x86_64 /usr/bin/cc -E -`
> Attempt Ctrl-C, the issue is reproduced.
>
> Reference:
> https://refspecs.linuxfoundation.org/ELF/ppc64/PPC-elf64abi-1.9.html#REG
>
> Signed-off-by: Shivaprasad G Bhat <sbhat@linux.vnet.ibm.com>
> Tested-by: Laurent Vivier <laurent@vivier.eu>
> Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Applied to ppc-for-3.0.
> ---
> v1: https://lists.gnu.org/archive/html/qemu-devel/2018-07/msg05089.html
> Changes from v1:
> Fixed the commit message as suggested
>
> linux-user/host/ppc64/safe-syscall.inc.S | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/linux-user/host/ppc64/safe-syscall.inc.S b/linux-user/host/ppc64/safe-syscall.inc.S
> index d30050a67c..b0cbbe6a69 100644
> --- a/linux-user/host/ppc64/safe-syscall.inc.S
> +++ b/linux-user/host/ppc64/safe-syscall.inc.S
> @@ -49,7 +49,7 @@ safe_syscall_base:
> * and returns the result in r3
> * Shuffle everything around appropriately.
> */
> - mr 11, 3 /* signal_pending */
> + mr 14, 3 /* signal_pending */
> mr 0, 4 /* syscall number */
> mr 3, 5 /* syscall arguments */
> mr 4, 6
> @@ -67,7 +67,7 @@ safe_syscall_base:
> */
> safe_syscall_start:
> /* if signal_pending is non-zero, don't do the call */
> - lwz 12, 0(11)
> + lwz 12, 0(14)
> cmpwi 0, 12, 0
> bne- 0f
> sc
>
>
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [Qemu-devel] [Qemu-ppc] [PATCH v2] linux-user: ppc64: don't use volatile register during safe_syscall
2018-07-27 3:13 ` [Qemu-devel] [Qemu-ppc] " David Gibson
@ 2018-07-27 5:20 ` Richard Henderson
2018-07-27 5:34 ` David Gibson
0 siblings, 1 reply; 4+ messages in thread
From: Richard Henderson @ 2018-07-27 5:20 UTC (permalink / raw)
To: David Gibson, Shivaprasad G Bhat
Cc: dgibson, riku.voipio, laurent, qemu-ppc, qemu-devel
On 07/26/2018 08:13 PM, David Gibson wrote:
> On Thu, Jul 26, 2018 at 01:56:19PM +0530, Shivaprasad G Bhat wrote:
>> r11 is a volatile register on PPC as per calling conventions.
>> The safe_syscall code uses it to check if the signal_pending
>> is set during the safe_syscall. When a syscall is interrupted
>> on return from signal handling, the r11 might be corrupted
>> before we retry the syscall leading to a crash. The registers
>> r0-r13 are not to be used here as they have
>> volatile/designated/reserved usages. Change the code to use
>> r14 which is non-volatile and is appropriate for local use in
>> safe_syscall.
>>
>> Steps to reproduce:
>> On PPC host, issue `qemu-x86_64 /usr/bin/cc -E -`
>> Attempt Ctrl-C, the issue is reproduced.
>>
>> Reference:
>> https://refspecs.linuxfoundation.org/ELF/ppc64/PPC-elf64abi-1.9.html#REG
>>
>> Signed-off-by: Shivaprasad G Bhat <sbhat@linux.vnet.ibm.com>
>> Tested-by: Laurent Vivier <laurent@vivier.eu>
>> Reviewed-by: Laurent Vivier <laurent@vivier.eu>
>
> Applied to ppc-for-3.0.
No please! r14 is a call-saved register and needs saving before clobbering.
r~
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [Qemu-devel] [Qemu-ppc] [PATCH v2] linux-user: ppc64: don't use volatile register during safe_syscall
2018-07-27 5:20 ` Richard Henderson
@ 2018-07-27 5:34 ` David Gibson
0 siblings, 0 replies; 4+ messages in thread
From: David Gibson @ 2018-07-27 5:34 UTC (permalink / raw)
To: Richard Henderson
Cc: Shivaprasad G Bhat, dgibson, riku.voipio, laurent, qemu-ppc,
qemu-devel
[-- Attachment #1: Type: text/plain, Size: 1487 bytes --]
On Thu, Jul 26, 2018 at 10:20:11PM -0700, Richard Henderson wrote:
> On 07/26/2018 08:13 PM, David Gibson wrote:
> > On Thu, Jul 26, 2018 at 01:56:19PM +0530, Shivaprasad G Bhat wrote:
> >> r11 is a volatile register on PPC as per calling conventions.
> >> The safe_syscall code uses it to check if the signal_pending
> >> is set during the safe_syscall. When a syscall is interrupted
> >> on return from signal handling, the r11 might be corrupted
> >> before we retry the syscall leading to a crash. The registers
> >> r0-r13 are not to be used here as they have
> >> volatile/designated/reserved usages. Change the code to use
> >> r14 which is non-volatile and is appropriate for local use in
> >> safe_syscall.
> >>
> >> Steps to reproduce:
> >> On PPC host, issue `qemu-x86_64 /usr/bin/cc -E -`
> >> Attempt Ctrl-C, the issue is reproduced.
> >>
> >> Reference:
> >> https://refspecs.linuxfoundation.org/ELF/ppc64/PPC-elf64abi-1.9.html#REG
> >>
> >> Signed-off-by: Shivaprasad G Bhat <sbhat@linux.vnet.ibm.com>
> >> Tested-by: Laurent Vivier <laurent@vivier.eu>
> >> Reviewed-by: Laurent Vivier <laurent@vivier.eu>
> >
> > Applied to ppc-for-3.0.
>
> No please! r14 is a call-saved register and needs saving before
> clobbering.
Oops, pulled out now.
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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^ permalink raw reply [flat|nested] 4+ messages in thread
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2018-07-26 8:26 [Qemu-devel] [PATCH v2] linux-user: ppc64: don't use volatile register during safe_syscall Shivaprasad G Bhat
2018-07-27 3:13 ` [Qemu-devel] [Qemu-ppc] " David Gibson
2018-07-27 5:20 ` Richard Henderson
2018-07-27 5:34 ` David Gibson
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