diff options
| author | Anton Blanchard <[email protected]> | 2016-05-20 04:41:34 +1000 |
|---|---|---|
| committer | Michael Ellerman <[email protected]> | 2016-07-26 14:16:19 +1000 |
| commit | dd57023747e33572b31867f890b0d99f55b5cc2f (patch) | |
| tree | b1c4d528032a2d3f594357965c122ff2c15298b2 | |
| parent | 1a1cee843c4a532f57083ffe8cbf4fcd3dcb381d (diff) | |
powerpc: Improve comment explaining why we modify VRSAVE
The comment explaining why we modify VRSAVE is misleading, glibc
does rely on the behaviour. Update the comment.
Signed-off-by: Anton Blanchard <[email protected]>
Reviewed-by: Cyril Bur <[email protected]>
Signed-off-by: Michael Ellerman <[email protected]>
| -rw-r--r-- | arch/powerpc/kernel/vector.S | 9 |
1 files changed, 5 insertions, 4 deletions
diff --git a/arch/powerpc/kernel/vector.S b/arch/powerpc/kernel/vector.S index 1c2e7a343bf5..616a6d854638 100644 --- a/arch/powerpc/kernel/vector.S +++ b/arch/powerpc/kernel/vector.S @@ -70,10 +70,11 @@ _GLOBAL(load_up_altivec) MTMSRD(r5) /* enable use of AltiVec now */ isync - /* Hack: if we get an altivec unavailable trap with VRSAVE - * set to all zeros, we assume this is a broken application - * that fails to set it properly, and thus we switch it to - * all 1's + /* + * While userspace in general ignores VRSAVE, glibc uses it as a boolean + * to optimise userspace context save/restore. Whenever we take an + * altivec unavailable exception we must set VRSAVE to something non + * zero. Set it to all 1s. See also the programming note in the ISA. */ mfspr r4,SPRN_VRSAVE cmpwi 0,r4,0 |