[PATCH] RISC-V: Clobber V state on system calls

[Palmer Dabbelt <palmer@rivosinc.com>]

The Linux uABI clobbers all V state on syscalls (similar to SVE), but
the syscall inline asm macros don't enforce this.  So just explicitly
clobber everything.

Reported-by: Vineet Gupta <vineetg@rivosinc.com>
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
---
Vineet's been debugging a userspace hang, and it looks like it's
uncovered at least three issues:

* Linux isn't properly tracking V state, which results in some
  signal-based userpace return paths missing the V state save.  This is
  almost certainly a Linux bug, Charlie is looking at it.
* GCC only discards the V register state on function calls, despite the
  ABI also mandating that the V CSR state is discarded.  I'm not 100% on
  this one as I don't really understand the vsetvl passes, but we were
  talking about it on the GCC call yesterday and that's our best guess
  right now.
* glibc doesn't mark the V state as clobbered by syscalls.

I don't know if we can actually manifest incorrect behavior here and it
definately doesn't build (GCC doesn't support vxsat [1]).  I'm sort of
just sending this as a placeholder, but I figured with all the other
chaos I should send it rather than risking forgetting about it.

[1]: https://inbox.sourceware.org/gcc-patches/20240327195403.29732-2-palmer@rivosinc.com/
---
 sysdeps/unix/sysv/linux/riscv/sysdep.h | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/sysdeps/unix/sysv/linux/riscv/sysdep.h b/sysdeps/unix/sysv/linux/riscv/sysdep.h
index ee015dfeb6..3e3971e321 100644
--- a/sysdeps/unix/sysv/linux/riscv/sysdep.h
+++ b/sysdeps/unix/sysv/linux/riscv/sysdep.h
@@ -354,7 +354,17 @@
 	_sys_result;							\
 })
 
+#ifdef __riscv_vector
+# define __SYSCALL_CLOBBERS "memory", "vl", "vtype", "vxrm", "vxsat",	\
+			    "v0",   "v1",  "v2",  "v3",  "v4",  "v5",	\
+			    "v6",   "v7",  "v8",  "v9", "v10", "v11",	\
+			    "v12", "v13", "v14", "v15", "v16", "v17",	\
+			    "v18", "v18", "v19", "v20", "v21", "v22",	\
+			    "v23", "v24", "v25", "v26", "v27", "v28",	\
+			    "v29", "v30", "v31"
+#else
 # define __SYSCALL_CLOBBERS "memory"
+#endif
 
 extern long int __syscall_error (long int neg_errno);
 
-- 
2.44.0