Re: [PATCH] linux-user: Fixed cpu restore with pc 0 on SIGBUS

[Palmer Dabbelt]

On Fri, 12 Jan 2024 12:57:22 PST (-0800), r...@rivosinc.com wrote:
Commit f4e1168198 (linux-user: Split out host_sig{segv,bus}_handler)
introduced a bug, when returning from host_sigbus_handler the PC is

So we should probably have a

Fixes: f4e1168198 ("linux-user: Split out host_sig{segv,bus}_handler")

never set. Thus cpu_loop_exit_restore is called with a zero PC and
we immediate get a SIGSEGV.

Signed-off-by: Robbin Ehn <r...@rivosinc.com>
---
 linux-user/signal.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/linux-user/signal.c b/linux-user/signal.c
index b35d1e512f..c9527adfa3 100644
--- a/linux-user/signal.c
+++ b/linux-user/signal.c
@@ -925,7 +925,7 @@ static void host_sigsegv_handler(CPUState *cpu, siginfo_t 
*info,
     cpu_loop_exit_sigsegv(cpu, guest_addr, access_type, maperr, pc);
 }
 
-static void host_sigbus_handler(CPUState *cpu, siginfo_t *info,
+static uintptr_t host_sigbus_handler(CPUState *cpu, siginfo_t *info,
                                 host_sigcontext *uc)
 {
     uintptr_t pc = host_signal_pc(uc);
@@ -947,6 +947,7 @@ static void host_sigbus_handler(CPUState *cpu, siginfo_t 
*info,
         sigprocmask(SIG_SETMASK, host_signal_mask(uc), NULL);
         cpu_loop_exit_sigbus(cpu, guest_addr, access_type, pc);
     }
+    return pc;
 }
 
 static void host_signal_handler(int host_sig, siginfo_t *info, void *puc)
@@ -974,7 +975,7 @@ static void host_signal_handler(int host_sig, siginfo_t 
*info, void *puc)
             host_sigsegv_handler(cpu, info, uc);

Do we have the same problem for SEGV?  They both used to set

   pc = host_signal_pc(uc);

but with this it's only SIGBUS.  Maybe the same for the others, so just 
something like

   diff --git a/linux-user/signal.c b/linux-user/signal.c
   index b35d1e512f..55840bdf31 100644
   --- a/linux-user/signal.c
   +++ b/linux-user/signal.c
   @@ -968,6 +968,8 @@ static void host_signal_handler(int host_sig, siginfo_t 
*info, void *puc)
         * SIGFPE, SIGTRAP are always host bugs.
         */
        if (info->si_code > 0) {
   +        pc = host_signal_pc(uc);
   +
            switch (host_sig) {
            case SIGSEGV:
                /* Only returns on handle_sigsegv_accerr_write success. */

as it just does the PC chasing for everyone?

             return;
         case SIGBUS:
-            host_sigbus_handler(cpu, info, uc);
+            pc = host_sigbus_handler(cpu, info, uc);
             sync_sig = true;
             break;
         case SIGILL:
--
2.40.1

Either way,

Reviewed-by: Palmer Dabbelt <pal...@rivosinc.com>

Thanks!