PowerPC64 ELFv2 -fpatchable-function-entry

[Alan Modra]

PowerPC64 ELFv2 dual entry point functions have a couple of problems
with -fpatchable-function-entry.  One is that the nops added after the
global entry land in the global entry code which is constrained to be
a power of two number of instructions, and zero global entry code has
special meaning for linkage.  The other is that the global entry code
isn't always used on function entry, and some uses of
-fpatchable-function-entry might want to affect all entries to the
function.  So this patch arranges to put one batch of nops before the
global entry, and the other after the local entry point.

	PR target/98125
	* config/rs6000/rs6000.c (rs6000_print_patchable_function_entry): New
	function.
	(TARGET_ASM_PRINT_PATCHABLE_FUNCTION_ENTRY): Define.
	* config/rs6000/rs6000-logue.c: Include targhooks.h.
	(rs6000_output_function_prologue): Handle nops for
	-fpatchable-function-entry after local entry point.

diff --git a/gcc/config/rs6000/rs6000-logue.c b/gcc/config/rs6000/rs6000-logue.c
index b0ac183ceff..ffa3bb3dcf1 100644
--- a/gcc/config/rs6000/rs6000-logue.c
+++ b/gcc/config/rs6000/rs6000-logue.c
@@ -51,6 +51,7 @@
 #include "gstab.h"  /* for N_SLINE */
 #include "dbxout.h" /* dbxout_ */
 #endif
+#include "targhooks.h"
 
 static int rs6000_ra_ever_killed (void);
 static void is_altivec_return_reg (rtx, void *);
@@ -3991,6 +3992,10 @@ rs6000_output_function_prologue (FILE *file)
       fputs (",1\n", file);
     }
 
+  int nops_after_entry = crtl->patch_area_size - crtl->patch_area_entry;
+  if (nops_after_entry > 0)
+    default_print_patchable_function_entry (file, nops_after_entry, false);
+
   /* Output -mprofile-kernel code.  This needs to be done here instead of
      in output_function_profile since it must go after the ELFv2 ABI
      local entry point.  */
diff --git a/gcc/config/rs6000/rs6000.c b/gcc/config/rs6000/rs6000.c
index d43c36e7f1a..97f1b3e0674 100644
--- a/gcc/config/rs6000/rs6000.c
+++ b/gcc/config/rs6000/rs6000.c
@@ -1404,6 +1404,10 @@ static const struct attribute_spec rs6000_attribute_table[] =
 #undef TARGET_ASM_FUNCTION_EPILOGUE
 #define TARGET_ASM_FUNCTION_EPILOGUE rs6000_output_function_epilogue
 
+#undef TARGET_ASM_PRINT_PATCHABLE_FUNCTION_ENTRY
+#define TARGET_ASM_PRINT_PATCHABLE_FUNCTION_ENTRY \
+  rs6000_print_patchable_function_entry
+
 #undef TARGET_ASM_OUTPUT_ADDR_CONST_EXTRA
 #define TARGET_ASM_OUTPUT_ADDR_CONST_EXTRA rs6000_output_addr_const_extra
 
@@ -14953,6 +14957,33 @@ rs6000_assemble_visibility (tree decl, int vis)
 }
 #endif
 
+/* Write NOPs into the asm outfile FILE around a function entry.  This
+   routine may be called twice per function to put NOPs before and after
+   the function entry.  If RECORD_P is true the location of the NOPs will
+   be recorded by default_print_patchable_function_entry in a special
+   object section called "__patchable_function_entries".  Disable output
+   of any NOPs for the second call.  Those, if any, are output by
+   rs6000_output_function_prologue.  This means that for ELFv2 any NOPs
+   after the function entry are placed after the local entry point, not
+   the global entry point.  NOPs after the entry may be found at
+   record_loc + nops_before * 4 + local_entry_offset.  This holds true
+   when nops_before is zero.  */
+
+static void
+rs6000_print_patchable_function_entry (FILE *file,
+				       unsigned HOST_WIDE_INT patch_area_size ATTRIBUTE_UNUSED,
+				       bool record_p)
+{
+  /* Always call default_print_patchable_function_entry when RECORD_P in
+     order to output the location of the NOPs, but use the size of the
+     area before the entry on both possible calls.  If RECORD_P is true
+     on the second call then the area before the entry was zero size and
+     thus no NOPs will be output.  */
+  if (record_p)
+    default_print_patchable_function_entry (file, crtl->patch_area_entry,
+					    record_p);
+}
+
 enum rtx_code
 rs6000_reverse_condition (machine_mode mode, enum rtx_code code)
 {