linux-user/hppa: Add signal trampoline for hppa target

In Linux kernel v5.18 the vDSO for signal trampoline was added.
This code mimiks the bare minimum of this vDSO and thus avoids that the
parisc emulation needs executable stacks.

Signed-off-by: Helge Deller <deller@gmx.de>
Message-Id: <20220924114501.21767-4-deller@gmx.de>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

linux-user/hppa/signal.c

@@ -41,7 +41,7 @@ struct target_ucontext {
 };
 
 struct target_rt_sigframe {
-    abi_uint tramp[9];
+    abi_uint tramp[2];  /* syscall restart return address */
     target_siginfo_t info;
     struct target_ucontext uc;
     /* hidden location of upper halves of pa2.0 64-bit gregs */
@@ -101,9 +101,15 @@ static void restore_sigcontext(CPUArchState *env, struct target_sigcontext *sc)
     __get_user(env->cr[CR_SAR], &sc->sc_sar);
 }
 
-/* No, this doesn't look right, but it's copied straight from the kernel.  */
+#if TARGET_ABI_BITS == 32
+#define SIGFRAME                64
+#define FUNCTIONCALLFRAME       48
+#else
+#define SIGFRAME                128
+#define FUNCTIONCALLFRAME       96
+#endif
 #define PARISC_RT_SIGFRAME_SIZE32 \
-    ((sizeof(struct target_rt_sigframe) + 48 + 64) & -64)
+    ((sizeof(struct target_rt_sigframe) + FUNCTIONCALLFRAME + SIGFRAME) & -SIGFRAME)
 
 void setup_rt_frame(int sig, struct target_sigaction *ka,
                     target_siginfo_t *info,
@@ -118,7 +124,7 @@ void setup_rt_frame(int sig, struct target_sigaction *ka,
     if ((ka->sa_flags & TARGET_SA_ONSTACK) && !sas_ss_flags(sp)) {
         sp = (ts->sigaltstack_used.ss_sp + 0x7f) & ~0x3f;
     }
-    frame_addr = QEMU_ALIGN_UP(sp, 64);
+    frame_addr = QEMU_ALIGN_UP(sp, SIGFRAME);
     sp = frame_addr + PARISC_RT_SIGFRAME_SIZE32;
 
     trace_user_setup_rt_frame(env, frame_addr);
@@ -139,14 +145,9 @@ void setup_rt_frame(int sig, struct target_sigaction *ka,
 
     setup_sigcontext(&frame->uc.tuc_mcontext, env);
 
-    __put_user(0x34190000, frame->tramp + 0); /* ldi 0,%r25 */
-    __put_user(0x3414015a, frame->tramp + 1); /* ldi __NR_rt_sigreturn,%r20 */
-    __put_user(0xe4008200, frame->tramp + 2); /* be,l 0x100(%sr2,%r0) */
-    __put_user(0x08000240, frame->tramp + 3); /* nop */
-
     unlock_user_struct(frame, frame_addr, 1);
 
-    env->gr[2] = h2g(frame->tramp);
+    env->gr[2] = default_rt_sigreturn;
     env->gr[30] = sp;
     env->gr[26] = sig;
     env->gr[25] = h2g(&frame->info);
@@ -197,3 +198,23 @@ long do_rt_sigreturn(CPUArchState *env)
     force_sig(TARGET_SIGSEGV);
     return -QEMU_ESIGRETURN;
 }
+
+void setup_sigtramp(abi_ulong sigtramp_page)
+{
+    uint32_t *tramp = lock_user(VERIFY_WRITE, sigtramp_page, 6*4, 0);
+    abi_ulong SIGFRAME_CONTEXT_REGS32;
+    assert(tramp != NULL);
+
+    SIGFRAME_CONTEXT_REGS32 = offsetof(struct target_rt_sigframe, uc.tuc_mcontext);
+    SIGFRAME_CONTEXT_REGS32 -= PARISC_RT_SIGFRAME_SIZE32;
+
+    __put_user(SIGFRAME_CONTEXT_REGS32, tramp + 0);
+    __put_user(0x08000240, tramp + 1);  /* nop - b/c dwarf2 unwind routines */
+    __put_user(0x34190000, tramp + 2);  /* ldi 0, %r25 (in_syscall=0) */
+    __put_user(0x3414015a, tramp + 3);  /* ldi __NR_rt_sigreturn, %r20 */
+    __put_user(0xe4008200, tramp + 4);  /* ble 0x100(%sr2, %r0) */
+    __put_user(0x08000240, tramp + 5);  /* nop */
+
+    default_rt_sigreturn = (sigtramp_page + 8) | 3;
+    unlock_user(tramp, sigtramp_page, 6*4);
+}

linux-user/hppa/target_signal.h

@@ -70,18 +70,6 @@ typedef struct target_sigaltstack {
 /* mask for all SS_xxx flags */
 #define TARGET_SS_FLAG_BITS  TARGET_SS_AUTODISARM
 
-/*
- * We cannot use a bare sigtramp page for hppa-linux.
- *
- * Unlike other guests where we use the instructions at PC to validate
- * an offset from SP, the hppa libgcc signal frame fallback unwinding uses
- * the PC address itself to find the frame.  This is due to the fact that
- * the hppa grows the stack upward, and the frame is of unknown size.
- *
- * TODO: We should be able to use a VDSO to address this, by providing
- * proper unwind info for the sigtramp code, at which point the fallback
- * unwinder will not be used.
- */
-#define TARGET_ARCH_HAS_SIGTRAMP_PAGE 0
+#define TARGET_ARCH_HAS_SIGTRAMP_PAGE 1
 
 #endif /* HPPA_TARGET_SIGNAL_H */