sigsegv: Fix compilation error on Android 4.3

[Bruno Haible]

On Android 4.3 (with the 'Terminal IDE' app), I'm seeing a compilation error
in the latest diffutils snapshot:

  CC       libdiffutils_a-c-stack.o
In file included from ../../lib/c-stack.c:52:
./sigsegv.h:33:23: error: ucontext.h: No such file or directory

And similarly in the latest grep snapshot.

The fix is in Gnulib's sigsegv module.


2023-01-02  Bruno Haible  <bruno@clisp.org>

        sigsegv: Fix compilation error on Android 4.3.
        * lib/sigsegv.in.h: For Android, don't include <ucontext.h> and don't
        reference ucontext_t.
        * lib/sigsegv.c (SIGSEGV_FAULT_): For Android, use a plain POSIX fault
        handler (cf. libsigsegv/src/fault-posix.h).

diff --git a/lib/sigsegv.in.h b/lib/sigsegv.in.h
index 097041f1ba..40b453e67b 100644
--- a/lib/sigsegv.in.h
+++ b/lib/sigsegv.in.h
@@ -23,7 +23,7 @@
 #include <stddef.h>

 /* Define the fault context structure.  */
-#if defined __linux__ || defined __ANDROID__ \
+#if (defined __linux__ && !defined __ANDROID__) \
     || (defined __FreeBSD__ && (defined __arm__ || defined __armhf__ || 
defined __arm64__)) \
     || defined __NetBSD__ \
     || defined _AIX || defined __sun \
@@ -180,7 +180,7 @@ extern int sigsegv_leave_handler (void (*continuation) 
(void*, void*, void*), vo
  * on some platforms it is a 'struct sigcontext *', on others merely an
  * opaque 'void *'.
  */
-# if defined __linux__ || defined __ANDROID__ \
+# if (defined __linux__ && !defined __ANDROID__) \
      || (defined __FreeBSD__ && (defined __arm__ || defined __armhf__ || 
defined __arm64__)) \
      || defined __NetBSD__ \
      || (defined __APPLE__ && defined __MACH__) \
diff --git a/lib/sigsegv.c b/lib/sigsegv.c
index 14f3a4650b..29c452dbe0 100644
--- a/lib/sigsegv.c
+++ b/lib/sigsegv.c
@@ -61,7 +61,7 @@ int libsigsegv_version = LIBSIGSEGV_VERSION;
           occurred.
  */
 
-#if defined __linux__ || defined __ANDROID__ /* Linux */
+#if defined __linux__ && !defined __ANDROID__ /* Linux */
 
 # define SIGSEGV_FAULT_HANDLER_ARGLIST  int sig, siginfo_t *sip, void *ucp
 # define SIGSEGV_FAULT_ADDRESS  sip->si_addr
@@ -348,6 +348,17 @@ int libsigsegv_version = LIBSIGSEGV_VERSION;
 
 #endif
 
+#if defined __ANDROID__ /* Android */
+/* A platform that supports the POSIX:2008 (XPG 7) way, without
+   'struct sigcontext' nor 'ucontext_t'.  */
+
+# define SIGSEGV_FAULT_HANDLER_ARGLIST  int sig, siginfo_t *sip, void *context
+# define SIGSEGV_FAULT_ADDRESS  sip->si_addr
+# define SIGSEGV_FAULT_CONTEXT  context
+# define SIGSEGV_FAULT_ADDRESS_FROM_SIGINFO
+
+#endif
+
 #if defined __GNU__ /* Hurd */
 
 # define SIGSEGV_FAULT_HANDLER_ARGLIST  int sig, int code, struct sigcontext 
*scp