[Qemu-devel] Trying to add usermode support for signalfd (but failing)

[Alex Barcelo]

I was trying to add signalfd support on qemu-ppc (specifically, I'm
doing a configure with "--enable-debug-tcg --enable-debug
--disable-strip --disable-kvm --disable-bsd-user --disable-darwin-user
--enable-profiler --target-list=ppc-linux-user --disable-curl
--enable-nptl").

At first I thought that it should be straightforward, so I simply
added the syscall to the "do_syscall" code. See the patch at the end.

The test program used is the example that can be found on the
signalfd(2) manpage.

It fails with a "qemu: Unsupported syscall: 313"... but the syscall
313 IS supported (it's the splice syscall, which the configure detects
and enables the CONFIG_SPLICE and it seems correct). I checked with a
splice-specific test --it worked as it should. I debugged a bit and it
seems that the switch ignores this syscall, but only when this 313
syscall is called from inside the signalfd syscall (it seems that
internally signalfd calls a splice). I am completely lost, I was
hoping that somebody could point me some directions.

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 2bf9e7e..bcf527f 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -57,6 +57,7 @@ int __clone2(int (*fn)(void *), void *child_stack_base,
 #include <sys/sysinfo.h>
 #include <sys/utsname.h>
 //#include <sys/user.h>
+#include <sys/signalfd.h>
 #include <netinet/ip.h>
 #include <netinet/tcp.h>
 #include <linux/wireless.h>
@@ -198,12 +199,14 @@ static type name (type1 arg1,type2 arg2,type3
arg3,type4 arg4,type5 arg5,     \
 #define __NR_sys_inotify_init __NR_inotify_init
 #define __NR_sys_inotify_add_watch __NR_inotify_add_watch
 #define __NR_sys_inotify_rm_watch __NR_inotify_rm_watch
+#define __NR_sys_signalfd __NR_signalfd

 #if defined(__alpha__) || defined (__ia64__) || defined(__x86_64__) || \
     defined(__s390x__)
 #define __NR__llseek __NR_lseek
 #endif

+_syscall3(int, sys_signalfd, int, fd, const sigset_t * , mask , int, flags);
 #ifdef __NR_gettid
 _syscall0(int, gettid)
 #else
@@ -8141,6 +8144,17 @@ abi_long do_syscall(void *cpu_env, int num,
abi_long arg1,
         break;
     }
 #endif
+    case TARGET_NR_signalfd:
+    {
+        sigset_t set, *set_ptr;
+
+        if (!(p = lock_user(VERIFY_READ, arg2, sizeof(target_sigset_t), 1)))
+            goto efault;
+        target_to_host_old_sigset(&set, p);
+        set_ptr = &set;
+       ret = get_errno(sys_signalfd(arg1,set_ptr,arg3) );
+       break;
+    }
     default:
     unimplemented:
         gemu_log("qemu: Unsupported syscall: %d\n", num);