| Message ID | 1467370393-7703-2-git-send-email-ard.biesheuvel@linaro.org |
|---|---|
| State | Accepted |
| Commit | 3b3593b567761d2568ea70c117c7111fd85e79b9 |
| Headers | show |
On Fri, Jul 01, 2016 at 12:53:13PM +0200, Ard Biesheuvel wrote: > SErrors (formerly called asynchronous aborts) are a distinct class of > exceptions that are not closely tied to the currently executing > instruction. Since execution may be able to proceed in such a condition, > this class of exception is masked by default, and software needs to unmask > it explicitly if it is prepared to handle such exceptions. > > On DEBUG builds, we are well equipped to report the CPU context to the user > and it makes sense to report an SError as soon as it occurs rather than to > wait for the OS to take it when it unmasks them, especially since the current > arm64/Linux implementation simply panics in that case. So unmask them when > ArmCpuDxe loads. > > Contributed-under: TianoCore Contribution Agreement 1.0 > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> > --- > ArmPkg/Drivers/CpuDxe/Exception.c | 9 +++++++++ > 1 file changed, 9 insertions(+) These look sensible to me. FWIW, for both patches: Acked-by: Mark Rutland <mark.rutland@arm.com> Mark. > > diff --git a/ArmPkg/Drivers/CpuDxe/Exception.c b/ArmPkg/Drivers/CpuDxe/Exception.c > index c3107cd4a6bc..d806a5fdf910 100644 > --- a/ArmPkg/Drivers/CpuDxe/Exception.c > +++ b/ArmPkg/Drivers/CpuDxe/Exception.c > @@ -62,6 +62,15 @@ InitializeExceptions ( > Status = Cpu->EnableInterrupt (Cpu); > } > > + // > + // On a DEBUG build, unmask SErrors so they are delivered right away rather > + // than when the OS unmasks them. This gives us a better chance of figuring > + // out the cause. > + // > + DEBUG_CODE ( > + ArmEnableAsynchronousAbort (); > + ); > + > return Status; > } > > -- > 2.7.4 > _______________________________________________ edk2-devel mailing list edk2-devel@lists.01.org https://lists.01.org/mailman/listinfo/edk2-devel
On Fri, Jul 01, 2016 at 12:53:13PM +0200, Ard Biesheuvel wrote: > SErrors (formerly called asynchronous aborts) are a distinct class of > exceptions that are not closely tied to the currently executing > instruction. Since execution may be able to proceed in such a condition, > this class of exception is masked by default, and software needs to unmask > it explicitly if it is prepared to handle such exceptions. > > On DEBUG builds, we are well equipped to report the CPU context to the user > and it makes sense to report an SError as soon as it occurs rather than to > wait for the OS to take it when it unmasks them, especially since the current > arm64/Linux implementation simply panics in that case. So unmask them when > ArmCpuDxe loads. So, I agree with this patch: Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org> But if we're doing this, I wonder if we should not also do so for non-DEBUG builds? Do we expect other operating systems to do anything useful with the exception? If not, hanging when the error occurs sounds more informative than hanging as soon as you start your OS. > Contributed-under: TianoCore Contribution Agreement 1.0 > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> > --- > ArmPkg/Drivers/CpuDxe/Exception.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/ArmPkg/Drivers/CpuDxe/Exception.c b/ArmPkg/Drivers/CpuDxe/Exception.c > index c3107cd4a6bc..d806a5fdf910 100644 > --- a/ArmPkg/Drivers/CpuDxe/Exception.c > +++ b/ArmPkg/Drivers/CpuDxe/Exception.c > @@ -62,6 +62,15 @@ InitializeExceptions ( > Status = Cpu->EnableInterrupt (Cpu); > } > > + // > + // On a DEBUG build, unmask SErrors so they are delivered right away rather > + // than when the OS unmasks them. This gives us a better chance of figuring > + // out the cause. > + // > + DEBUG_CODE ( > + ArmEnableAsynchronousAbort (); > + ); > + > return Status; > } > > -- > 2.7.4 > _______________________________________________ edk2-devel mailing list edk2-devel@lists.01.org https://lists.01.org/mailman/listinfo/edk2-devel
On 1 July 2016 at 13:03, Leif Lindholm <leif.lindholm@linaro.org> wrote: > On Fri, Jul 01, 2016 at 12:53:13PM +0200, Ard Biesheuvel wrote: >> SErrors (formerly called asynchronous aborts) are a distinct class of >> exceptions that are not closely tied to the currently executing >> instruction. Since execution may be able to proceed in such a condition, >> this class of exception is masked by default, and software needs to unmask >> it explicitly if it is prepared to handle such exceptions. >> >> On DEBUG builds, we are well equipped to report the CPU context to the user >> and it makes sense to report an SError as soon as it occurs rather than to >> wait for the OS to take it when it unmasks them, especially since the current >> arm64/Linux implementation simply panics in that case. So unmask them when >> ArmCpuDxe loads. > > So, I agree with this patch: > Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org> > > But if we're doing this, I wonder if we should not also do so for > non-DEBUG builds? Do we expect other operating systems to do anything > useful with the exception? If not, hanging when the error occurs > sounds more informative than hanging as soon as you start your OS. > Well, the point is that we send debug output only to the serial port, and you can reasonably expect someone running a DEBUG build to be monitoring its output. On a RELEASE build, it makes more sense for the OS to handle it (although panicking as early as arm64 linux does is not very helpful either) since it will hang without any feedback to the UEFI console (even the RELEASE code in the default exception handler writes to the serial port directly rather than to UEFI's console) _______________________________________________ edk2-devel mailing list edk2-devel@lists.01.org https://lists.01.org/mailman/listinfo/edk2-devel
On Fri, Jul 01, 2016 at 01:21:36PM +0200, Ard Biesheuvel wrote: > On 1 July 2016 at 13:03, Leif Lindholm <leif.lindholm@linaro.org> wrote: > > On Fri, Jul 01, 2016 at 12:53:13PM +0200, Ard Biesheuvel wrote: > >> SErrors (formerly called asynchronous aborts) are a distinct class of > >> exceptions that are not closely tied to the currently executing > >> instruction. Since execution may be able to proceed in such a condition, > >> this class of exception is masked by default, and software needs to unmask > >> it explicitly if it is prepared to handle such exceptions. > >> > >> On DEBUG builds, we are well equipped to report the CPU context to the user > >> and it makes sense to report an SError as soon as it occurs rather than to > >> wait for the OS to take it when it unmasks them, especially since the current > >> arm64/Linux implementation simply panics in that case. So unmask them when > >> ArmCpuDxe loads. > > > > So, I agree with this patch: > > Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org> > > > > But if we're doing this, I wonder if we should not also do so for > > non-DEBUG builds? Do we expect other operating systems to do anything > > useful with the exception? If not, hanging when the error occurs > > sounds more informative than hanging as soon as you start your OS. > > > > Well, the point is that we send debug output only to the serial port, > and you can reasonably expect someone running a DEBUG build to be > monitoring its output. On a RELEASE build, it makes more sense for the > OS to handle it (although panicking as early as arm64 linux does is > not very helpful either) since it will hang without any feedback to > the UEFI console (even the RELEASE code in the default exception > handler writes to the serial port directly rather than to UEFI's > console) No, I follow that logic completely. I agree it is a lot less useful without the debug output. However, I am asking if it is still not providing more information to the user if the firmware hangs when an untraceable exception happens during boot, than if the operating system hangs at a specific point regardless where the SError was triggered. If we say "other operating systems may handle this better, or at least be able to successfully boot", then that is a decent argument to only ASSERT on DEBUG. / Leif _______________________________________________ edk2-devel mailing list edk2-devel@lists.01.org https://lists.01.org/mailman/listinfo/edk2-devel
On 1 July 2016 at 15:48, Leif Lindholm <leif.lindholm@linaro.org> wrote: > On Fri, Jul 01, 2016 at 01:21:36PM +0200, Ard Biesheuvel wrote: >> On 1 July 2016 at 13:03, Leif Lindholm <leif.lindholm@linaro.org> wrote: >> > On Fri, Jul 01, 2016 at 12:53:13PM +0200, Ard Biesheuvel wrote: >> >> SErrors (formerly called asynchronous aborts) are a distinct class of >> >> exceptions that are not closely tied to the currently executing >> >> instruction. Since execution may be able to proceed in such a condition, >> >> this class of exception is masked by default, and software needs to unmask >> >> it explicitly if it is prepared to handle such exceptions. >> >> >> >> On DEBUG builds, we are well equipped to report the CPU context to the user >> >> and it makes sense to report an SError as soon as it occurs rather than to >> >> wait for the OS to take it when it unmasks them, especially since the current >> >> arm64/Linux implementation simply panics in that case. So unmask them when >> >> ArmCpuDxe loads. >> > >> > So, I agree with this patch: >> > Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org> >> > >> > But if we're doing this, I wonder if we should not also do so for >> > non-DEBUG builds? Do we expect other operating systems to do anything >> > useful with the exception? If not, hanging when the error occurs >> > sounds more informative than hanging as soon as you start your OS. >> > >> >> Well, the point is that we send debug output only to the serial port, >> and you can reasonably expect someone running a DEBUG build to be >> monitoring its output. On a RELEASE build, it makes more sense for the >> OS to handle it (although panicking as early as arm64 linux does is >> not very helpful either) since it will hang without any feedback to >> the UEFI console (even the RELEASE code in the default exception >> handler writes to the serial port directly rather than to UEFI's >> console) > > No, I follow that logic completely. > I agree it is a lot less useful without the debug output. > > However, I am asking if it is still not providing more information to > the user if the firmware hangs when an untraceable exception happens > during boot, than if the operating system hangs at a specific point > regardless where the SError was triggered. > > If we say "other operating systems may handle this better, or at least > be able to successfully boot", then that is a decent argument to only > ASSERT on DEBUG. > I think it is fundamentally the firmware's job to deal with these conditions if it can, but hanging with a black screen is simply not very helpful. On a RELEASE build, being able to make it to the UEFI shell or to a setup screen that at least tells you which version of the firmware you are running is probably more useful than knowing that the SError occurred very early on. _______________________________________________ edk2-devel mailing list edk2-devel@lists.01.org https://lists.01.org/mailman/listinfo/edk2-devel
diff --git a/ArmPkg/Drivers/CpuDxe/Exception.c b/ArmPkg/Drivers/CpuDxe/Exception.c index c3107cd4a6bc..d806a5fdf910 100644 --- a/ArmPkg/Drivers/CpuDxe/Exception.c +++ b/ArmPkg/Drivers/CpuDxe/Exception.c @@ -62,6 +62,15 @@ InitializeExceptions ( Status = Cpu->EnableInterrupt (Cpu); } + // + // On a DEBUG build, unmask SErrors so they are delivered right away rather + // than when the OS unmasks them. This gives us a better chance of figuring + // out the cause. + // + DEBUG_CODE ( + ArmEnableAsynchronousAbort (); + ); + return Status; }
SErrors (formerly called asynchronous aborts) are a distinct class of exceptions that are not closely tied to the currently executing instruction. Since execution may be able to proceed in such a condition, this class of exception is masked by default, and software needs to unmask it explicitly if it is prepared to handle such exceptions. On DEBUG builds, we are well equipped to report the CPU context to the user and it makes sense to report an SError as soon as it occurs rather than to wait for the OS to take it when it unmasks them, especially since the current arm64/Linux implementation simply panics in that case. So unmask them when ArmCpuDxe loads. Contributed-under: TianoCore Contribution Agreement 1.0 Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> --- ArmPkg/Drivers/CpuDxe/Exception.c | 9 +++++++++ 1 file changed, 9 insertions(+) -- 2.7.4 _______________________________________________ edk2-devel mailing list edk2-devel@lists.01.org https://lists.01.org/mailman/listinfo/edk2-devel