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linux-user/sparc: call block_signals() before set_sigmask() in setcontext

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sparc64_set_context() emulates the kernel's `ta 0x6f` trap by calling
set_sigmask() to install the mask supplied via the user's ucontext_t.
The contract of set_sigmask() (see its comment in linux-user/signal.c)
is that the caller must have first called block_signals(), which sets
TaskState::signal_pending.

Without block_signals(), if a guest signal is pending-and-blocked at
the time setcontext is invoked and the new mask unblocks it,
signal_pending stays 0 and the post-trap process_pending_signals()
call in linux-user/sparc/cpu_loop.c never enters its while loop, so
the now-deliverable signal is left undelivered indefinitely.

This affects programs that use getcontext/setcontext to swap signal
masks, including libunwind's unw_resume() out of a signal handler:
without this fix, the test program below loops forever printing
"calling setcontext" instead of delivering the pending SIGUSR2.

  #define _GNU_SOURCE
  #include <ucontext.h>
  #include <signal.h>
  #include <stdio.h>
  #include <unistd.h>
  static int got;
  static void h(int s) { got = 1; }
  int main(void) {
      signal(SIGUSR2, h);
      sigset_t m; sigemptyset(&m); sigaddset(&m, SIGUSR2);
      sigprocmask(SIG_BLOCK, &m, NULL);
      kill(getpid(), SIGUSR2);
      ucontext_t uc;
      getcontext(&uc);
      if (got) return 0;
      uc.uc_sigmask.__val[0] = 0;
      setcontext(&uc);
      return 1;
  }

The 32-bit sparc do_sigreturn / do_rt_sigreturn paths already get
block_signals() from the rt_sigreturn syscall wrapper in
linux-user/syscall.c, so only sparc64_set_context (invoked directly
from cpu_loop) needs the addition.

Signed-off-by: Matt Turner <mattst88@gmail.com>
Cc: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Signed-off-by: Helge Deller <deller@gmx.de>
This commit is contained in:
Matt Turner
2026-06-03 12:18:51 -04:00
committed by Helge Deller
parent 14a27b0fd8
commit e0f0ce88eb
1 changed files with 9 additions and 0 deletions
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9
linux-user/sparc/signal.c
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@@ -619,6 +619,15 @@ void sparc64_set_context(CPUSPARCState *env)
}
}
target_to_host_sigset_internal(&set, &target_set);
/*
* set_sigmask() requires the caller to have first called
* block_signals() so that process_pending_signals() is guaranteed
* to run after the mask change. Without this, a guest signal that
* is pending-and-blocked at setcontext time is left undelivered
* even after its mask bit is cleared, because signal_pending stays
* 0 and the post-trap process_pending_signals() loop never enters.
*/
block_signals();
set_sigmask(&set);
}
env->pc = pc;