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[v5,21/26] linux-user/s390x: Implement setup_sigtramp

Message ID 20210929130553.121567-22-richard.henderson@linaro.org
State New
Headers show
Series linux-user: Move signal trampolines to new page | expand

Commit Message

Richard Henderson Sept. 29, 2021, 1:05 p.m. UTC 
Create and record the two signal trampolines.
Use them when the guest does not use SA_RESTORER.

Cc: qemu-s390x@nongnu.org
Tested-by: Alex Bennée <alex.bennee@linaro.org>

Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

---
 linux-user/s390x/target_signal.h |  2 ++
 linux-user/s390x/signal.c        | 24 ++++++++++++++++--------
 2 files changed, 18 insertions(+), 8 deletions(-)

-- 
2.25.1

Comments

Richard Henderson April 29, 2022, 6:14 p.m. UTC | #1 
On 4/28/22 11:15, Ulrich Weigand wrote:
> 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.)

Ah, quite right -- I had read the comment for sigframe,

         __u16 svc_insn;         /* Offset of svc_insn is NOT fixed! */


and incorrectly assumed that applied to rt_sigframe too.
So, yes, the second hunk should be reverted, with a comment that it is not used and not 
even initialized by the kernel.


r~
diff mbox series

Patch

diff --git a/linux-user/s390x/target_signal.h b/linux-user/s390x/target_signal.h
index bbfc464d44..64f5f42201 100644
--- a/linux-user/s390x/target_signal.h
+++ b/linux-user/s390x/target_signal.h
@@ -19,4 +19,6 @@  typedef struct target_sigaltstack {
 #include "../generic/signal.h"
 
 #define TARGET_ARCH_HAS_SETUP_FRAME
+#define TARGET_ARCH_HAS_SIGTRAMP_PAGE 1
+
 #endif /* S390X_TARGET_SIGNAL_H */
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;
@@ -209,9 +207,7 @@  void setup_frame(int sig, struct target_sigaction *ka,
     if (ka->sa_flags & TARGET_SA_RESTORER) {
         restorer = ka->sa_restorer;
     } else {
-        restorer = frame_addr + offsetof(sigframe, retcode);
-        __put_user(S390_SYSCALL_OPCODE | TARGET_NR_sigreturn,
-                   &frame->retcode);
+        restorer = default_sigreturn;
     }
 
     /* Set up registers for signal handler */
@@ -262,9 +258,7 @@  void setup_rt_frame(int sig, struct target_sigaction *ka,
     if (ka->sa_flags & TARGET_SA_RESTORER) {
         restorer = ka->sa_restorer;
     } else {
-        restorer = frame_addr + offsetof(typeof(*frame), retcode);
-        __put_user(S390_SYSCALL_OPCODE | TARGET_NR_rt_sigreturn,
-                   &frame->retcode);
+        restorer = default_rt_sigreturn;
     }
 
     /* Create siginfo on the signal stack. */
@@ -405,3 +399,17 @@  long do_rt_sigreturn(CPUS390XState *env)
     unlock_user_struct(frame, frame_addr, 0);
     return -TARGET_QEMU_ESIGRETURN;
 }
+
+void setup_sigtramp(abi_ulong sigtramp_page)
+{
+    uint16_t *tramp = lock_user(VERIFY_WRITE, sigtramp_page, 2 + 2, 0);
+    assert(tramp != NULL);
+
+    default_sigreturn = sigtramp_page;
+    __put_user(S390_SYSCALL_OPCODE | TARGET_NR_sigreturn, &tramp[0]);
+
+    default_rt_sigreturn = sigtramp_page + 2;
+    __put_user(S390_SYSCALL_OPCODE | TARGET_NR_rt_sigreturn, &tramp[1]);
+
+    unlock_user(tramp, sigtramp_page, 2 + 2);
+}