rs6000: Avoid -fpatchable-function-entry* regressions on powerpc64 be [PR98125]

The SECTION_LINK_ORDER changes broke powerpc64-linux ELFv1.  Seems
that the assembler/linker relies on the symbol mentioned for the
"awo" section to be in the same section as the symbols mentioned in
the relocations in that section (i.e. labels for the patchable area
in this case).  That is the case for most targets, including powerpc-linux
32-bit or powerpc64 ELFv2 (that one has -fpatchable-function-entry*
support broken for other reasons and it doesn't seem to be a regression).
But it doesn't work on powerpc64-linux ELFv1.
We emit:
        .section        ".opd","aw"
        .align 3
_Z3foov:
        .quad   .L._Z3foov,.TOC.@tocbase,0
        .previous
        .type   _Z3foov, @function
.L._Z3foov:
        .section        __patchable_function_entries,"awo",@progbits,_Z3foov
        .align 3
        .8byte  .LPFE1
        .section        .text._Z3foov,"axG",@progbits,_Z3foov,comdat
.LPFE1:
        nop
.LFB0:
        .cfi_startproc
and because _Z3foov is in the .opd section rather than the function text
section, it doesn't work.

I'm afraid I don't know what exactly should be done, whether e.g.
it could use
        .section        __patchable_function_entries,"awo",@progbits,.L._Z3foov
instead, or whether the linker should be changed to handle it as is, or
something else.

But because we have a P1 regression that didn't see useful progress over the
4 months since it has been filed and we don't really have much time, below
is an attempt to do a targetted reversion of H.J's patch, basically act as
if HAVE_GAS_SECTION_LINK_ORDER is never true for powerpc64-linux ELFv1,
but for 32-bit or 64-bit ELFv2 keep working as is.
This would give us time to resolve it for GCC 12 properly.

2021-04-03  Jakub Jelinek  <jakub@redhat.com>

	PR testsuite/98125
	* targhooks.h (default_print_patchable_function_entry_1): Declare.
	* targhooks.c (default_print_patchable_function_entry_1): New function,
	copied from default_print_patchable_function_entry with an added flags
	argument.
	(default_print_patchable_function_entry): Rewritten into a small
	wrapper around default_print_patchable_function_entry_1.
	* config/rs6000/rs6000.c (TARGET_ASM_PRINT_PATCHABLE_FUNCTION_ENTRY):
	Redefine.
	(rs6000_print_patchable_function_entry): New function.

	* g++.dg/pr93195a.C: Skip on powerpc*-*-* 64-bit.

diff --git a/gcc/config/rs6000/rs6000.c b/gcc/config/rs6000/rs6000.c
index befab53031c664166cecffb086f67c147f0d7a46..35f5c332c41ca3d74695281ced1d63c6de9fe0b5 100644 (file)
--- a/gcc/config/rs6000/rs6000.c
+++ b/gcc/config/rs6000/rs6000.c
@@ -1341,6 +1341,10 @@ static const struct attribute_spec rs6000_attribute_table[] =
 #define TARGET_ASM_ASSEMBLE_VISIBILITY rs6000_assemble_visibility
 #endif
 
+#undef TARGET_ASM_PRINT_PATCHABLE_FUNCTION_ENTRY
+#define TARGET_ASM_PRINT_PATCHABLE_FUNCTION_ENTRY \
+  rs6000_print_patchable_function_entry
+
 #undef TARGET_SET_UP_BY_PROLOGUE
 #define TARGET_SET_UP_BY_PROLOGUE rs6000_set_up_by_prologue
 
@@ -14695,6 +14699,30 @@ rs6000_assemble_visibility (tree decl, int vis)
 }
 #endif
 \f
+/* Write PATCH_AREA_SIZE NOPs into the asm outfile FILE around a function
+   entry.  If RECORD_P is true and the target supports named sections,
+   the location of the NOPs will be recorded in a special object section
+   called "__patchable_function_entries".  This routine may be called
+   twice per function to put NOPs before and after the function
+   entry.  */
+
+void
+rs6000_print_patchable_function_entry (FILE *file,
+                                      unsigned HOST_WIDE_INT patch_area_size,
+                                      bool record_p)
+{
+  unsigned int flags = SECTION_WRITE | SECTION_RELRO;
+  /* When .opd section is emitted, the function symbol
+     default_print_patchable_function_entry_1 is emitted into the .opd section
+     while the patchable area is emitted into the function section.
+     Don't use SECTION_LINK_ORDER in that case.  */
+  if (!(TARGET_64BIT && DEFAULT_ABI != ABI_ELFv2)
+      && HAVE_GAS_SECTION_LINK_ORDER)
+    flags |= SECTION_LINK_ORDER;
+  default_print_patchable_function_entry_1 (file, patch_area_size, record_p,
+                                           flags);
+}
+\f
 enum rtx_code
 rs6000_reverse_condition (machine_mode mode, enum rtx_code code)
 {

diff --git a/gcc/targhooks.c b/gcc/targhooks.c
index d69c9a2d8199fd4d84551893ef4dc9a1657e88d0..952fad422ebdecf1ba90d47ce64691ebab40ec36 100644 (file)
--- a/gcc/targhooks.c
+++ b/gcc/targhooks.c
@@ -1832,17 +1832,15 @@ default_compare_by_pieces_branch_ratio (machine_mode)
   return 1;
 }
 
-/* Write PATCH_AREA_SIZE NOPs into the asm outfile FILE around a function
-   entry.  If RECORD_P is true and the target supports named sections,
-   the location of the NOPs will be recorded in a special object section
-   called "__patchable_function_entries".  This routine may be called
-   twice per function to put NOPs before and after the function
-   entry.  */
+/* Helper for default_print_patchable_function_entry and other
+   print_patchable_function_entry hook implementations.  */
 
 void
-default_print_patchable_function_entry (FILE *file,
-                                       unsigned HOST_WIDE_INT patch_area_size,
-                                       bool record_p)
+default_print_patchable_function_entry_1 (FILE *file,
+                                         unsigned HOST_WIDE_INT
+                                         patch_area_size,
+                                         bool record_p,
+                                         unsigned int flags)
 {
   const char *nop_templ = 0;
   int code_num;
@@ -1864,9 +1862,6 @@ default_print_patchable_function_entry (FILE *file,
       patch_area_number++;
       ASM_GENERATE_INTERNAL_LABEL (buf, "LPFE", patch_area_number);
 
-      unsigned int flags = SECTION_WRITE | SECTION_RELRO;
-      if (HAVE_GAS_SECTION_LINK_ORDER)
-       flags |= SECTION_LINK_ORDER;
       switch_to_section (get_section ("__patchable_function_entries",
                                      flags, current_function_decl));
       assemble_align (POINTER_SIZE);
@@ -1883,6 +1878,25 @@ default_print_patchable_function_entry (FILE *file,
     output_asm_insn (nop_templ, NULL);
 }
 
+/* Write PATCH_AREA_SIZE NOPs into the asm outfile FILE around a function
+   entry.  If RECORD_P is true and the target supports named sections,
+   the location of the NOPs will be recorded in a special object section
+   called "__patchable_function_entries".  This routine may be called
+   twice per function to put NOPs before and after the function
+   entry.  */
+
+void
+default_print_patchable_function_entry (FILE *file,
+                                       unsigned HOST_WIDE_INT patch_area_size,
+                                       bool record_p)
+{
+  unsigned int flags = SECTION_WRITE | SECTION_RELRO;
+  if (HAVE_GAS_SECTION_LINK_ORDER)
+    flags |= SECTION_LINK_ORDER;
+  default_print_patchable_function_entry_1 (file, patch_area_size, record_p,
+                                           flags);
+}
+
 bool
 default_profile_before_prologue (void)
 {

diff --git a/gcc/targhooks.h b/gcc/targhooks.h
index 39a6f82f143f4d29698fd65a5d687459bfc30ef5..9928d064abd5e3726bd3bce1ef5340031b427e84 100644 (file)
--- a/gcc/targhooks.h
+++ b/gcc/targhooks.h
@@ -230,6 +230,9 @@ extern bool default_use_by_pieces_infrastructure_p (unsigned HOST_WIDE_INT,
                                                    bool);
 extern int default_compare_by_pieces_branch_ratio (machine_mode);
 
+extern void default_print_patchable_function_entry_1 (FILE *,
+                                                     unsigned HOST_WIDE_INT,
+                                                     bool, unsigned int);
 extern void default_print_patchable_function_entry (FILE *,
                                                    unsigned HOST_WIDE_INT,
                                                    bool);

diff --git a/gcc/testsuite/g++.dg/pr93195a.C b/gcc/testsuite/g++.dg/pr93195a.C
index 26d265da74ebf7754a1724c0ba5694c5b28d03b3..b14f1b3e34189b06c0472489ee5e63a637fcfae4 100644 (file)
--- a/gcc/testsuite/g++.dg/pr93195a.C
+++ b/gcc/testsuite/g++.dg/pr93195a.C
@@ -1,4 +1,5 @@
 /* { dg-do link { target { ! { nvptx*-*-* visium-*-* } } } } */
+/* { dg-skip-if "not supported" { { powerpc*-*-* } && lp64 } } */
 // { dg-require-effective-target o_flag_in_section }
 /* { dg-options "-O0 -fpatchable-function-entry=1" } */
 /* { dg-additional-options "-fno-pie" { target sparc*-*-* } } */