| Message ID | 20190716205034.42466-1-abrodkin@synopsys.com |
|---|---|
| State | New |
| Headers | show |
| Series | ARCv2: Don't pretend we may set U & DE bits in STATUS32 with kflag | expand |
On 7/16/19 1:51 PM, Alexey Brodkin wrote: > As per PRM "kflag" instruction doesn't change state of > DE-flag ("Delayed branch is pending") and U-flag ("User mode") > in STATUS32 register so let's not act as if we can affect those bits. I understand the motivation and indeed bits not writable by kflag should be removed. But what if we do need to clear those bits out from status32 (assuming they exist there in first place) and that kflag might not be the right instruction to do that. So the question to ask is do we need to clear U and DE bits from status32 and answer from reading the PRM is no, we don't have to, as those are cleared already when an exception is taken. The likely reason this code is because back in arc700 days we used to have a different version of this macro which atleast in original code relied on using the pre-exception status32 (in pt_regs) - and that could easily have U and/or DE set based hence needed clearing. .macro FAKE_RET_FROM_EXCPN reg ld \reg, [sp, PT_status32] and \reg, \reg, ~(STATUS_U_MASK|STATUS_DE_MASK) or \reg, \reg, STATUS_L_MASK sr \reg, [erstatus] mov \reg, 55f sr \reg, [eret] rtie 55: .endm This is not needed (even in arc700) if we are using the current "in-exception" status32 for doing the early return. Long story short, your patch is correct but we need to explain better why it is. I've applied it locally with slight tweak to changelog to that effect. > Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com> > --- > arch/arc/include/asm/entry-arcv2.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/arc/include/asm/entry-arcv2.h b/arch/arc/include/asm/entry-arcv2.h > index 225e7df2d8ed..6558e2edb583 100644 > --- a/arch/arc/include/asm/entry-arcv2.h > +++ b/arch/arc/include/asm/entry-arcv2.h > @@ -237,7 +237,7 @@ > > .macro FAKE_RET_FROM_EXCPN > lr r9, [status32] > - bic r9, r9, (STATUS_U_MASK|STATUS_DE_MASK|STATUS_AE_MASK) > + bic r9, r9, STATUS_AE_MASK > or r9, r9, STATUS_IE_MASK > kflag r9 > .endm
diff --git a/arch/arc/include/asm/entry-arcv2.h b/arch/arc/include/asm/entry-arcv2.h index 225e7df2d8ed..6558e2edb583 100644 --- a/arch/arc/include/asm/entry-arcv2.h +++ b/arch/arc/include/asm/entry-arcv2.h @@ -237,7 +237,7 @@ .macro FAKE_RET_FROM_EXCPN lr r9, [status32] - bic r9, r9, (STATUS_U_MASK|STATUS_DE_MASK|STATUS_AE_MASK) + bic r9, r9, STATUS_AE_MASK or r9, r9, STATUS_IE_MASK kflag r9 .endm
As per PRM "kflag" instruction doesn't change state of DE-flag ("Delayed branch is pending") and U-flag ("User mode") in STATUS32 register so let's not act as if we can affect those bits. Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com> --- arch/arc/include/asm/entry-arcv2.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)