[PULL 20/38] linux-user/hppa: Add signal trampoline for hppa target

[Laurent Vivier <laurent@vivier.eu>]

From: Helge Deller <deller@gmx.de>

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 +++++++++++++++++++++++++--------
 linux-user/hppa/target_signal.h | 14 +----------
 2 files changed, 32 insertions(+), 23 deletions(-)

diff --git a/linux-user/hppa/signal.c b/linux-user/hppa/signal.c
index 962f551c0429..396e310dc92d 100644
--- a/linux-user/hppa/signal.c
+++ b/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);
+}
diff --git a/linux-user/hppa/target_signal.h b/linux-user/hppa/target_signal.h
index af6c2fce589d..190bb3d653b6 100644
--- a/linux-user/hppa/target_signal.h
+++ b/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 */
-- 
2.37.3