linux-user/riscv: Implement setup_sigtramp

Create and record the rt signal trampoline.

This fixes a bug wrt libgcc fallback unwinding.  It expects
the stack pointer to point to the siginfo_t, whereas we had
inexplicably placed our private signal trampoline at the start
of the signal frame instead of the end.  Now moot because we
have removed it from the stack frame entirely.

Reviewed-by: Alistair Francis <[email protected]>
Reviewed-by: Philippe Mathieu-Daudé <[email protected]>
Signed-off-by: Richard Henderson <[email protected]>
Message-Id: <[email protected]>
Signed-off-by: Laurent Vivier <[email protected]>

Author: rth7680

linux-user/riscv/signal.c

@@ -47,7 +47,6 @@ struct target_ucontext {
 };
 
 struct target_rt_sigframe {
-    uint32_t tramp[2]; /* not in kernel, which uses VDSO instead */
     struct target_siginfo info;
     struct target_ucontext uc;
 };
@@ -105,12 +104,6 @@ static void setup_ucontext(struct target_ucontext *uc,
     setup_sigcontext(&uc->uc_mcontext, env);
 }
 
-static inline void install_sigtramp(uint32_t *tramp)
-{
-    __put_user(0x08b00893, tramp + 0);  /* li a7, 139 = __NR_rt_sigreturn */
-    __put_user(0x00000073, tramp + 1);  /* ecall */
-}
-
 void setup_rt_frame(int sig, struct target_sigaction *ka,
                     target_siginfo_t *info,
                     target_sigset_t *set, CPURISCVState *env)
@@ -127,14 +120,13 @@ void setup_rt_frame(int sig, struct target_sigaction *ka,
 
     setup_ucontext(&frame->uc, env, set);
     tswap_siginfo(&frame->info, info);
-    install_sigtramp(frame->tramp);
 
     env->pc = ka->_sa_handler;
     env->gpr[xSP] = frame_addr;
     env->gpr[xA0] = sig;
     env->gpr[xA1] = frame_addr + offsetof(struct target_rt_sigframe, info);
     env->gpr[xA2] = frame_addr + offsetof(struct target_rt_sigframe, uc);
-    env->gpr[xRA] = frame_addr + offsetof(struct target_rt_sigframe, tramp);
+    env->gpr[xRA] = default_rt_sigreturn;
 
     return;
 
@@ -203,3 +195,15 @@ long do_rt_sigreturn(CPURISCVState *env)
     force_sig(TARGET_SIGSEGV);
     return 0;
 }
+
+void setup_sigtramp(abi_ulong sigtramp_page)
+{
+    uint32_t *tramp = lock_user(VERIFY_WRITE, sigtramp_page, 8, 0);
+    assert(tramp != NULL);
+
+    __put_user(0x08b00893, tramp + 0);  /* li a7, 139 = __NR_rt_sigreturn */
+    __put_user(0x00000073, tramp + 1);  /* ecall */
+
+    default_rt_sigreturn = sigtramp_page;
+    unlock_user(tramp, sigtramp_page, 8);
+}

linux-user/riscv/target_signal.h

@@ -15,4 +15,6 @@ typedef struct target_sigaltstack {
 
 #include "../generic/signal.h"
 
+#define TARGET_ARCH_HAS_SIGTRAMP_PAGE 1
+
 #endif /* RISCV_TARGET_SIGNAL_H */