rts: don't define RTS_USER_SIGNALS when signal.h is not present

In the rts, we have a RTS_USER_SIGNALS macro, and most signal-related
logic is guarded with RTS_USER_SIGNALS. This patch extends the range
of code guarded with RTS_USER_SIGNALS, and define RTS_USER_SIGNALS iff
signal.h is actually detected by autoconf. This is required for
wasm32-wasi to work, which lacks signals.

7 files changed, 32 insertions, 7 deletions

diff --git a/rts/IOManager.c b/rts/IOManager.c
index e9bf3fa70c..6606b82e06 100644
--- a/rts/IOManager.c
+++ b/rts/IOManager.c
@@ -21,7 +21,7 @@
 #include "Capability.h"
 #include "RtsFlags.h"
 
-#if !defined(mingw32_HOST_OS)
+#if !defined(mingw32_HOST_OS) && defined(HAVE_SIGNAL_H)
 #include "posix/Signals.h"
 #endif
 
diff --git a/rts/Linker.c b/rts/Linker.c
index 3121cc38df..ed60d14b62 100644
--- a/rts/Linker.c
+++ b/rts/Linker.c
@@ -36,7 +36,7 @@
 #include "CheckUnload.h" // createOCSectionIndices
 #include "ReportMemoryMap.h"
 
-#if !defined(mingw32_HOST_OS)
+#if !defined(mingw32_HOST_OS) && defined(HAVE_SIGNAL_H)
 #include "posix/Signals.h"
 #endif
 
diff --git a/rts/RtsSignals.h b/rts/RtsSignals.h
index b0add6727d..c143737474 100644
--- a/rts/RtsSignals.h
+++ b/rts/RtsSignals.h
@@ -8,7 +8,7 @@
 
 #pragma once
 
-#if !defined(mingw32_HOST_OS)
+#if !defined(mingw32_HOST_OS) && defined(HAVE_SIGNAL_H)
 
 #include "posix/Signals.h"
 
@@ -22,7 +22,7 @@
 
 #endif
 
-#if RTS_USER_SIGNALS
+#if defined(RTS_USER_SIGNALS)
 
 #include "BeginPrivate.h"
 
diff --git a/rts/RtsStartup.c b/rts/RtsStartup.c
index 5b0cc9f712..46749163dc 100644
--- a/rts/RtsStartup.c
+++ b/rts/RtsStartup.c
@@ -659,7 +659,7 @@ shutdownHaskellAndExit(int n, int fastExit)
     stg_exit(n);
 }
 
-#if !defined(mingw32_HOST_OS)
+#if !defined(mingw32_HOST_OS) && defined(HAVE_SIGNAL_H)
 static void exitBySignal(int sig) STG_NORETURN;
 
 void
diff --git a/rts/RtsSymbols.c b/rts/RtsSymbols.c
index 64545d2e09..96a8d1cdb3 100644
--- a/rts/RtsSymbols.c
+++ b/rts/RtsSymbols.c
@@ -18,7 +18,7 @@
 #include "sm/NonMovingMark.h"
 #include <stdbool.h>
 
-#if !defined(mingw32_HOST_OS)
+#if !defined(mingw32_HOST_OS) && defined(HAVE_SIGNAL_H)
 #include "posix/Signals.h"
 #endif
 
diff --git a/rts/include/rts/Config.h b/rts/include/rts/Config.h
index c5f34638e0..0f923205f5 100644
--- a/rts/include/rts/Config.h
+++ b/rts/include/rts/Config.h
@@ -44,7 +44,32 @@
    Signals - supported on non-PAR versions of the runtime.  See RtsSignals.h.
    -------------------------------------------------------------------------- */
 
+/*
+Note [Lack of signals on wasm32-wasi]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+In the wasm32-wasi spec, there is no process/thread model, no
+preemptive execution, and no posix-style asynchronous signals. See
+WASI ticket #166 for upstream discussion about signal handling.
+
+In wasi-libc, signal.h includes an #error pragma in the default
+setting that says: "wasm lacks signal support; to enable minimal
+signal emulation, compile with -D_WASI_EMULATED_SIGNAL and link with
+-lwasi-emulated-signal". It is possible to enable these flags when
+configuring wasm32-wasi-ghc, but it still makes little sense, since
+the emulation is really primitive and we might as well just stop
+pretending signals exist at all.
+
+Therefore, in the entire GHC tree, whenever we define functionality
+related to posix signals, we should add the CPP guards. When the
+target lacks signals, we can't set signal handlers at all, and raising
+a signal should degrade to exiting with the signal number as the exit
+code.
+*/
+
+#if defined(HAVE_SIGNAL_H)
 #define RTS_USER_SIGNALS 1
+#endif
 
 /* Profile spin locks */
 
diff --git a/rts/posix/Signals.h b/rts/posix/Signals.h
index 8203f28b34..f1941727b3 100644
--- a/rts/posix/Signals.h
+++ b/rts/posix/Signals.h
@@ -18,7 +18,7 @@
 
 bool anyUserHandlers(void);
 
-#if !defined(THREADED_RTS)
+#if !defined(THREADED_RTS) && defined(RTS_USER_SIGNALS)
 extern siginfo_t pending_handler_buf[];
 extern siginfo_t *next_pending_handler;
 #define signals_pending() (next_pending_handler != pending_handler_buf)