s390x regression - Re: [PATCH v5 21/26] linux-user/s390x: Implement setup_sigtramp

[Ulrich Weigand]

Richard Henderson <richard.henderson@linaro.org> wrote:

>Create and record the two signal trampolines.
>Use them when the guest does not use SA_RESTORER.

This patch caused a regression when running the wasmtime CI under qemu:
https://github.com/bytecodealliance/wasmtime/pull/4076

The problem is that this part:

>diff --git a/linux-user/s390x/signal.c b/linux-user/s390x/signal.c
>index 80f34086d7..676b948147 100644
>--- a/linux-user/s390x/signal.c
>+++ b/linux-user/s390x/signal.c
>@@ -68,7 +68,6 @@ typedef struct {
>     target_sigregs sregs;
>     int signo;
>     target_sigregs_ext sregs_ext;
>-    uint16_t retcode;
> } sigframe;
> 
> #define TARGET_UC_VXRS 2
>@@ -85,7 +84,6 @@ struct target_ucontext {
> 
> typedef struct {
>     uint8_t callee_used_stack[__SIGNAL_FRAMESIZE];
>-    uint16_t retcode;
>     struct target_siginfo info;
>     struct target_ucontext uc;
> } rt_sigframe;

changes the layout of the signal stack frame that is visible from user
space.  Some user space code, in particular the GCC unwinder
(s390_fallback_frame_state in libgcc), relies on that layout and no
longer works correctly if it is changed.


Reverting just those two hunks above on top of QEMU 7.0 makes the
wasmtime CI pass again.  (Actually, just the second hunk is enough; the
first hunk is not visible since the removed variable is at the very top
of the frame.)


Bye,
Ulrich