RE: [PATCH] Handling SIGSETXID used by glibc NPTL setuid/setgid

[Taylor Simpson <tsimpson@quicinc.com>]

I proposed a similar patch guarded by #ifdef TARGET_HEXAGON.  I understand we don't want to break things that are working, and we don't want to open the door for a bunch of #ifdef's here.  However, more than one scenario needs this capability.

Would a suitable compromise be to provide a hook in linux-user/signal.c for the target to put in the changes they need?

diff --git a/linux-user/hexagon/target_signal.h b/linux-user/hexagon/target_signal.h
index ae52ff5..f82f8c1 100644
--- a/linux-user/hexagon/target_signal.h
+++ b/linux-user/hexagon/target_signal.h
@@ -31,4 +31,15 @@ typedef struct target_sigaltstack {

 #include "../generic/signal.h"

+    /*
+     * Hexagon uses the same signal for pthread cancel as the host pthreads,
+     * so cannot be overridden.
+     * Therefore, we map Hexagon signal to a different host signal.
+     */
+#define SIGNAL_MODS \
+    [__SIGRTMIN + 1] = __SIGRTMAX - 1, \
+    [__SIGRTMAX - 1] = __SIGRTMIN + 1,
+
+
+
 #endif /* TARGET_SIGNAL_H */
diff --git a/linux-user/signal.c b/linux-user/signal.c
index 5ca6d62..ebca770 100644
--- a/linux-user/signal.c
+++ b/linux-user/signal.c
@@ -24,6 +24,7 @@
 #include "qemu.h"
 #include "trace.h"
 #include "signal-common.h"
+#include "target_signal.h"

 static struct target_sigaction sigact_table[TARGET_NSIG];

@@ -72,6 +73,9 @@ static uint8_t host_to_target_signal_table[_NSIG] = {
        over a single host signal.  */
     [__SIGRTMIN] = __SIGRTMAX,
     [__SIGRTMAX] = __SIGRTMIN,
+#ifdef SIGNAL_MODS
+    SIGNAL_MODS
+#endif
 };
 static uint8_t target_to_host_signal_table[_NSIG];


Taylor


> -----Original Message-----
> From: Qemu-devel <qemu-devel-
> bounces+tsimpson=quicinc.com@nongnu.org> On Behalf Of Peter Maydell
> Sent: Tuesday, January 28, 2020 3:27 AM
> To: Matus Kysel <mkysel@tachyum.com>
> Cc: Riku Voipio <riku.voipio@iki.fi>; open list:All patches CC here <qemu-
> devel@nongnu.org>; Laurent Vivier <laurent@vivier.eu>
> Subject: Re: [PATCH] Handling SIGSETXID used by glibc NPTL setuid/setgid
>
> -------------------------------------------------------------------------
> CAUTION: This email originated from outside of the organization.
> -------------------------------------------------------------------------
>
> On Thu, 16 Jan 2020 at 11:58, Matus Kysel <mkysel@tachyum.com> wrote:
> >
> > Used same style to handle another glibc reserved signal SIGSETXID
> > (33), that is used by glibc NPTL setuid/setgid functions. This should
> > fix problems with application using those functions and failing with
> > error "qemu:handle_cpu_signal received signal outside vCPU context".
> >
> > Signed-off-by: Matus Kysel <mkysel@tachyum.com>
> > ---
> >  linux-user/signal.c | 13 +++++++++----
> >  1 file changed, 9 insertions(+), 4 deletions(-)
> >
> > diff --git a/linux-user/signal.c b/linux-user/signal.c index
> > 0128bde4d2..c59221fd0a 100644
> > --- a/linux-user/signal.c
> > +++ b/linux-user/signal.c
> > @@ -66,11 +66,16 @@ static uint8_t host_to_target_signal_table[_NSIG] =
> {
> >      [SIGPWR] = TARGET_SIGPWR,
> >      [SIGSYS] = TARGET_SIGSYS,
> >      /* next signals stay the same */
> > -    /* Nasty hack: Reverse SIGRTMIN and SIGRTMAX to avoid overlap with
> > -       host libpthread signals.  This assumes no one actually uses SIGRTMAX :-
> /
> > -       To fix this properly we need to do manual signal delivery multiplexed
> > -       over a single host signal.  */
> > +    /*
> > +     * Nasty hack: Swap SIGRTMIN and SIGRTMIN + 1 with SIGRTMAX and
> SIGRTMAX - 1
> > +     * to avoid overlap with host libpthread (NPTL glibc) signals.
> > +     * This assumes no one actually uses SIGRTMAX and SIGRTMAX - 1 :-/
> > +     * To fix this properly we need to do manual signal delivery multiplexed
> > +     * over a single host signal.
> > +     */
> >      [__SIGRTMIN] = __SIGRTMAX,
> > +    [__SIGRTMIN + 1] = __SIGRTMAX - 1,
> > +    [__SIGRTMAX - 1] = __SIGRTMIN + 1,
> >      [__SIGRTMAX] = __SIGRTMIN,
> >  };
> >  static uint8_t target_to_host_signal_table[_NSIG];
> > --
> > 2.17.1
>
> This is a long-standing known problem, but doing this is likely to break
> currently-working guest binaries (notably things written in Go). See for
> example the discussion on this thread:
> https://lists.gnu.org/archive/html/qemu-devel/2019-08/msg03804.html
>
> thanks
> -- PMM