rs6000: Enable -fasynchronous-unwind-tables by default

To find out where on-entry register values live at any point in a
program, GDB currently tries to parse to parse the executable code.
This does not work very well, for example it gets confused if some
accesses to the stack use the frame pointer (r31) and some use the
stack pointer (r1).  A symptom is that backtraces can be cut short.

This patch enables -fasynchronous-unwind-tables by default for rs6000,
which causes us to emit DWARF unwind tables for all functions, solving
these problems.

This not do anything for sub-targets without DWARF, and only for ELF
sub-targets for now.

It increases executable size, but only modestly, and does not change
memory use, only the disk image.


	* common/config/rs6000/rs6000-common.c (rs6000_option_init_struct):
	Enable -fasynchronous-unwind-tables by default if OBJECT_FORMAT_ELF.

gcc/testsuite/
	* gcc.target/powerpc/dfmode_off.c: Add -fno-asynchronous-unwind-tables.
	* gcc.target/powerpc/dimode_off.c: Ditto.
	* gcc.target/powerpc/tfmode_off.c: Ditto.
	* gcc.target/powerpc/timode_off.c: Ditto.

From-SVN: r259298

gcc/ChangeLog

 2018-04-10  Segher Boessenkool  <segher@kernel.crashing.org>
 
+	* common/config/rs6000/rs6000-common.c (rs6000_option_init_struct):
+	Enable -fasynchronous-unwind-tables by default if OBJECT_FORMAT_ELF.
+
+2018-04-10  Segher Boessenkool  <segher@kernel.crashing.org>
+
 	PR target/85321
 	* config/rs6000/rs6000.opt (mtraceback=): Show the allowed values in
 	the help text.

gcc/common/config/rs6000/rs6000-common.c

@@ -49,6 +49,15 @@ rs6000_option_init_struct (struct gcc_options *opts)
   /* Enable section anchors by default.  */
   if (!TARGET_MACHO)
     opts->x_flag_section_anchors = 1;
+
+  /* By default, always emit DWARF-2 unwind info.  This allows debugging
+     without maintaining a stack frame back-chain.  It also allows the
+     debugger to find out where on-entry register values are stored at any
+     point in a function, without having to analyze the executable code (which
+     isn't even possible to do in the general case).  */
+#ifdef OBJECT_FORMAT_ELF
+  opts->x_flag_asynchronous_unwind_tables = 1;
+#endif
 }
 
 /* Implement TARGET_OPTION_DEFAULT_PARAMS.  */

gcc/testsuite/ChangeLog

+2018-04-10  Segher Boessenkool  <segher@kernel.crashing.org>
+
+	* gcc.target/powerpc/dfmode_off.c: Add -fno-asynchronous-unwind-tables.
+	* gcc.target/powerpc/dimode_off.c: Ditto.
+	* gcc.target/powerpc/tfmode_off.c: Ditto.
+	* gcc.target/powerpc/timode_off.c: Ditto.
+
 2018-04-10  Kelvin Nilsen  <kelvin@gcc.gnu.org>
 
 	* gcc.target/powerpc/vec-ldl-1.c: New test.

gcc/testsuite/gcc.target/powerpc/dfmode_off.c

 /* { dg-do assemble } */
-/* { dg-options "-O2 -fno-align-functions -mtraceback=no -save-temps" } */
+/* { dg-options "-O2 -fno-align-functions -fno-asynchronous-unwind-tables -mtraceback=no -save-temps" } */
 
 void w1 (void *x, double y) { *(double *) (x + 32767) = y; }
 void w2 (void *x, double y) { *(double *) (x + 32766) = y; }

gcc/testsuite/gcc.target/powerpc/dimode_off.c

 /* { dg-do assemble } */
-/* { dg-options "-O2 -fno-align-functions -mtraceback=no -save-temps" } */
+/* { dg-options "-O2 -fno-align-functions -fno-asynchronous-unwind-tables -mtraceback=no -save-temps" } */
 
 void w1 (void *x, long long y) { *(long long *) (x + 32767) = y; }
 void w2 (void *x, long long y) { *(long long *) (x + 32766) = y; }

gcc/testsuite/gcc.target/powerpc/tfmode_off.c

@@ -2,7 +2,7 @@
 /* { dg-skip-if "" { powerpc-ibm-aix* } } */
 /* { dg-skip-if "no TFmode" { powerpc-*-eabi* } } */
 /* { dg-require-effective-target longdouble128 } */
-/* { dg-options "-O2 -fno-align-functions -mtraceback=no -save-temps" } */
+/* { dg-options "-O2 -fno-align-functions -fno-asynchronous-unwind-tables -mtraceback=no -save-temps" } */
 
 typedef float TFmode __attribute__ ((mode (TF)));
 

gcc/testsuite/gcc.target/powerpc/timode_off.c

 /* { dg-do assemble { target { lp64 } } } */
 /* { dg-skip-if "do not override -mcpu" { powerpc*-*-* } { "-mcpu=*" } { "-mcpu=power5" } } */
-/* { dg-options "-O2 -fno-align-functions -mtraceback=no -save-temps -mcpu=power5" } */
+/* { dg-options "-O2 -fno-align-functions -fno-asynchronous-unwind-tables -mtraceback=no -save-temps -mcpu=power5" } */
 
 typedef int TImode __attribute__ ((mode (TI)));