[PATCH] Documentation: RISC-V: uabi: Only scalar misaligned loads are supported

Palmer Dabbelt palmer at rivosinc.com
Fri May 24 11:56:00 PDT 2024


From: Palmer Dabbelt <palmer at rivosinc.com>

We're stuck supporting scalar misaligned loads in userspace because they
were part of the ISA at the time we froze the uABI.  That wasn't the
case for vector misaligned accesses, so depending on them
unconditionally is a userspace bug.  All extant vector hardware traps on
these misaligned accesses.

Signed-off-by: Palmer Dabbelt <palmer at rivosinc.com>
---
 Documentation/arch/riscv/uabi.rst | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/Documentation/arch/riscv/uabi.rst b/Documentation/arch/riscv/uabi.rst
index 54d199dce78b..2b420bab0527 100644
--- a/Documentation/arch/riscv/uabi.rst
+++ b/Documentation/arch/riscv/uabi.rst
@@ -65,4 +65,6 @@ the extension, or may have deliberately removed it from the listing.
 Misaligned accesses
 -------------------
 
-Misaligned accesses are supported in userspace, but they may perform poorly.
+Misaligned scalar accesses are supported in userspace, but they may perform
+poorly.  Misaligned vector accesses are only supported if the Zicclsm extension
+is supported.
-- 
2.45.0




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