[Qemu-devel] [PATCH] linux-user: Handle microMIPS encoding when processing trap exceptions

[Qemu-devel] [PATCH] linux-user: Handle microMIPS encoding when processing trap exceptions

[Kwok Cheung Yeung]

Decode trap instructions during the handling of a EXCP_TRAP according to
the current ISA mode.

Signed-off-by: Kwok Cheung Yeung <kcy@codesourcery.com>
---
 linux-user/main.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/linux-user/main.c b/linux-user/main.c
index 7f15d3d..c417e26 100644
--- a/linux-user/main.c
+++ b/linux-user/main.c
@@ -2379,7 +2379,10 @@ done_syscall:
 
                 /* The immediate versions don't provide a code.  */
                 if (!(trap_instr & 0xFC000000)) {
-                    code = ((trap_instr >> 6) & ((1 << 10) - 1));
+                    if (env->hflags & MIPS_HFLAG_M16)   /* microMIPS mode */
+                        code = ((trap_instr >> 12) & ((1 << 4) - 1));
+                    else
+                        code = ((trap_instr >> 6) & ((1 << 10) - 1));
                 }
 
                 if (do_break(env, &info, code) != 0) {
-- 
1.8.3.3

Re: [Qemu-devel] [PATCH] linux-user: Handle microMIPS encoding when processing trap exceptions

[Peter Maydell]

On 17 July 2013 17:50, Kwok Cheung Yeung <kcy@codesourcery.com> wrote:
> Decode trap instructions during the handling of a EXCP_TRAP according to
> the current ISA mode.
>
> Signed-off-by: Kwok Cheung Yeung <kcy@codesourcery.com>
> ---
>  linux-user/main.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/linux-user/main.c b/linux-user/main.c
> index 7f15d3d..c417e26 100644
> --- a/linux-user/main.c
> +++ b/linux-user/main.c
> @@ -2379,7 +2379,10 @@ done_syscall:
>
>                  /* The immediate versions don't provide a code.  */
>                  if (!(trap_instr & 0xFC000000)) {

So this trap_instr is read in QEMU via a simple get_user_ual(),
whereas if you look at the Linux kernel:
http://lxr.linux.no/#linux+v3.10.1/arch/mips/kernel/traps.c#L904

it specifically does two 16 bit loads for the microMIPS case.
Are you sure this code is correct for both big and little
endian MIPS configs?

(Similar remarks apply for EXCP_BREAK.)

> -                    code = ((trap_instr >> 6) & ((1 << 10) - 1));
> +                    if (env->hflags & MIPS_HFLAG_M16)   /* microMIPS mode */
> +                        code = ((trap_instr >> 12) & ((1 << 4) - 1));
> +                    else
> +                        code = ((trap_instr >> 6) & ((1 << 10) - 1));

This if statement needs braces to fit QEMU coding style.
scripts/checkpatch.pl will tell you about this sort of thing.

thanks
-- PMM