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 <alistair.francis@wdc.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20210929130553.121567-21-richard.henderson@linaro.org>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

1 files changed, 13 insertions, 9 deletions

diff --git a/linux-user/riscv/signal.c b/linux-user/riscv/signal.c
index f7f33bc90a..a0f9542ce3 100644
--- a/linux-user/riscv/signal.c
+++ b/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 @@ badframe:
     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);
+}