V4 [PATCH 0/3] Switch to a new section if the SECTION_RETAIN bit doesn't match

V4 [PATCH 0/3] Switch to a new section if the SECTION_RETAIN bit doesn't match

[H.J. Lu]

When SECTION_RETAIN is used, definitions marked with used attribute and
unmarked definitions are placed in a section with the same name.  Instead
of issue an error:

[hjl@gnu-cfl-2 gcc]$ /usr/gcc-11.0.0-x32/bin/gcc -S c.c -fdiagnostics-plain-output
c.c:2:49: error: ‘foo1’ causes a section type conflict with ‘foo2’
c.c:1:54: note: ‘foo2’ was declared here
[hjl@gnu-cfl-2 gcc]$

the first patch switches to a new section if the SECTION_RETAIN bit
doesn't match.  The second optional patch issues a warning:

[hjl@gnu-cfl-2 gcc]$ ./xgcc -B./ -S c.c
c.c:2:49: warning: ‘foo1’ without ‘used’ attribute and ‘foo2’ with ‘used’ attribute are placed in a section with the same name [-Wattributes]
    2 | const int __attribute__((section(".data.foo"))) foo1 = 1;
      |                                                 ^~~~
c.c:1:54: note: ‘foo2’ was declared here
    1 | const int __attribute__((used,section(".data.foo"))) foo2 = 2;
      |
[hjl@gnu-cfl-2 gcc]$

Changes from V3:

1. Add DECL_P (decl) to switch_to_section ().
2. Update comments for get_section ().
3. Require .init_array/.fini_array support for SHF_GNU_RETAIN.

Changes from V2:

1. Add (new_section->common.flags & SECTION_NAMED) check since
SHF_GNU_RETAIN section must be named.
2. Move c-c++-common/attr-used-9.c to the fist patch since there are
no new warnings.
3. Check new warnings only for R_flag_in_section target.


H.J. Lu (3):
  Switch to a new section if the SECTION_RETAIN bit doesn't match
  Warn used and not used symbols in section with the same name
  Require .init_array/.fini_array support for SHF_GNU_RETAIN

 gcc/defaults.h                           | 11 +++++
 gcc/output.h                             |  2 +-
 gcc/testsuite/c-c++-common/attr-used-5.c | 27 ++++++++++++
 gcc/testsuite/c-c++-common/attr-used-6.c | 27 ++++++++++++
 gcc/testsuite/c-c++-common/attr-used-7.c |  9 ++++
 gcc/testsuite/c-c++-common/attr-used-8.c |  9 ++++
 gcc/testsuite/c-c++-common/attr-used-9.c | 28 ++++++++++++
 gcc/testsuite/lib/target-supports.exp    |  2 +-
 gcc/varasm.c                             | 56 ++++++++++++++++++++----
 9 files changed, 161 insertions(+), 10 deletions(-)
 create mode 100644 gcc/testsuite/c-c++-common/attr-used-5.c
 create mode 100644 gcc/testsuite/c-c++-common/attr-used-6.c
 create mode 100644 gcc/testsuite/c-c++-common/attr-used-7.c
 create mode 100644 gcc/testsuite/c-c++-common/attr-used-8.c
 create mode 100644 gcc/testsuite/c-c++-common/attr-used-9.c

-- 
2.29.2

V4 [PATCH 1/3] Switch to a new section if the SECTION_RETAIN bit doesn't match

[H.J. Lu]

When definitions marked with used attribute and unmarked definitions are
placed in the section with the same name, switch to a new section if the
SECTION_RETAIN bit doesn't match.

gcc/

	PR target/98146
	* output.h (switch_to_section): Add a tree argument, default to
	nullptr.
	* varasm.c (get_section): If the SECTION_RETAIN bit doesn't match,
	return and switch to a new section later.
	(assemble_start_function): Pass decl to switch_to_section.
	(assemble_variable): Likewise.
	(switch_to_section): If the SECTION_RETAIN bit doesn't match,
	switch to a new section.

gcc/testsuite/

	PR target/98146
	* c-c++-common/attr-used-5.c: New test.
	* c-c++-common/attr-used-6.c: Likewise.
	* c-c++-common/attr-used-7.c: Likewise.
	* c-c++-common/attr-used-8.c: Likewise.
	* c-c++-common/attr-used-9.c: Likewise.
---
 gcc/output.h                             |  2 +-
 gcc/testsuite/c-c++-common/attr-used-5.c | 26 ++++++++++++++++++
 gcc/testsuite/c-c++-common/attr-used-6.c | 26 ++++++++++++++++++
 gcc/testsuite/c-c++-common/attr-used-7.c |  8 ++++++
 gcc/testsuite/c-c++-common/attr-used-8.c |  8 ++++++
 gcc/testsuite/c-c++-common/attr-used-9.c | 28 +++++++++++++++++++
 gcc/varasm.c                             | 34 ++++++++++++++++++++----
 7 files changed, 126 insertions(+), 6 deletions(-)
 create mode 100644 gcc/testsuite/c-c++-common/attr-used-5.c
 create mode 100644 gcc/testsuite/c-c++-common/attr-used-6.c
 create mode 100644 gcc/testsuite/c-c++-common/attr-used-7.c
 create mode 100644 gcc/testsuite/c-c++-common/attr-used-8.c
 create mode 100644 gcc/testsuite/c-c++-common/attr-used-9.c

diff --git a/gcc/output.h b/gcc/output.h
index fa8ace1f394..1f9af46da1d 100644
--- a/gcc/output.h
+++ b/gcc/output.h
@@ -548,7 +548,7 @@ extern void switch_to_other_text_partition (void);
 extern section *get_cdtor_priority_section (int, bool);
 
 extern bool unlikely_text_section_p (section *);
-extern void switch_to_section (section *);
+extern void switch_to_section (section *, tree = nullptr);
 extern void output_section_asm_op (const void *);
 
 extern void record_tm_clone_pair (tree, tree);
diff --git a/gcc/testsuite/c-c++-common/attr-used-5.c b/gcc/testsuite/c-c++-common/attr-used-5.c
new file mode 100644
index 00000000000..9fc0d3834e9
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/attr-used-5.c
@@ -0,0 +1,26 @@
+/* { dg-do compile } */
+/* { dg-options "-Wall -O2" } */
+
+struct dtv_slotinfo_list
+{
+  struct dtv_slotinfo_list *next;
+};
+
+extern struct dtv_slotinfo_list *list;
+
+static int __attribute__ ((section ("__libc_freeres_fn")))
+free_slotinfo (struct dtv_slotinfo_list **elemp)
+{
+  if (!free_slotinfo (&(*elemp)->next))
+    return 0;
+  return 1;
+}
+
+__attribute__ ((used, section ("__libc_freeres_fn")))
+static void free_mem (void)
+{
+  free_slotinfo (&list);
+}
+
+/* { dg-final { scan-assembler "__libc_freeres_fn,\"ax\"" { target R_flag_in_section } } } */
+/* { dg-final { scan-assembler "__libc_freeres_fn,\"axR\"" { target R_flag_in_section } } } */
diff --git a/gcc/testsuite/c-c++-common/attr-used-6.c b/gcc/testsuite/c-c++-common/attr-used-6.c
new file mode 100644
index 00000000000..0cb82ade5a9
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/attr-used-6.c
@@ -0,0 +1,26 @@
+/* { dg-do compile } */
+/* { dg-options "-Wall -O2" } */
+
+struct dtv_slotinfo_list
+{
+  struct dtv_slotinfo_list *next;
+};
+
+extern struct dtv_slotinfo_list *list;
+
+static int __attribute__ ((used, section ("__libc_freeres_fn")))
+free_slotinfo (struct dtv_slotinfo_list **elemp)
+{
+  if (!free_slotinfo (&(*elemp)->next))
+    return 0;
+  return 1;
+}
+
+__attribute__ ((section ("__libc_freeres_fn")))
+void free_mem (void)
+{
+  free_slotinfo (&list);
+}
+
+/* { dg-final { scan-assembler "__libc_freeres_fn,\"ax\"" { target R_flag_in_section } } } */
+/* { dg-final { scan-assembler "__libc_freeres_fn,\"axR\"" { target R_flag_in_section } } } */
diff --git a/gcc/testsuite/c-c++-common/attr-used-7.c b/gcc/testsuite/c-c++-common/attr-used-7.c
new file mode 100644
index 00000000000..fba2706ffc1
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/attr-used-7.c
@@ -0,0 +1,8 @@
+/* { dg-do compile } */
+/* { dg-options "-Wall -O2" } */
+
+int __attribute__((used,section(".data.foo"))) foo2 = 2;
+int __attribute__((section(".data.foo"))) foo1 = 1;
+
+/* { dg-final { scan-assembler ".data.foo,\"aw\"" { target R_flag_in_section } } } */
+/* { dg-final { scan-assembler ".data.foo,\"awR\"" { target R_flag_in_section } } } */
diff --git a/gcc/testsuite/c-c++-common/attr-used-8.c b/gcc/testsuite/c-c++-common/attr-used-8.c
new file mode 100644
index 00000000000..4da4aabe573
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/attr-used-8.c
@@ -0,0 +1,8 @@
+/* { dg-do compile } */
+/* { dg-options "-Wall -O2" } */
+
+int __attribute__((section(".data.foo"))) foo1 = 1;
+int __attribute__((used,section(".data.foo"))) foo2 = 2;
+
+/* { dg-final { scan-assembler ".data.foo,\"aw\"" { target R_flag_in_section } } } */
+/* { dg-final { scan-assembler ".data.foo,\"awR\"" { target R_flag_in_section } } } */
diff --git a/gcc/testsuite/c-c++-common/attr-used-9.c b/gcc/testsuite/c-c++-common/attr-used-9.c
new file mode 100644
index 00000000000..cf3bde67622
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/attr-used-9.c
@@ -0,0 +1,28 @@
+/* { dg-do compile } */
+/* { dg-options "-Wall -O2" } */
+
+struct dtv_slotinfo_list
+{
+  struct dtv_slotinfo_list *next;
+};
+
+extern struct dtv_slotinfo_list *list;
+
+static int __attribute__ ((used, section ("__libc_freeres_fn")))
+free_slotinfo (struct dtv_slotinfo_list **elemp)
+{
+  if (!free_slotinfo (&(*elemp)->next))
+    return 0;
+  return 1;
+}
+
+__attribute__ ((section ("__libc_freeres_fn")))
+static void free_mem (void)
+/* { dg-warning "defined but not used" "" { target *-*-* } .-1 } */
+{
+  free_slotinfo (&list);
+}
+
+/* { dg-final { scan-assembler-not "__libc_freeres_fn\n" } } */
+/* { dg-final { scan-assembler-not "__libc_freeres_fn,\"ax\"" { target R_flag_in_section } } } */
+/* { dg-final { scan-assembler "__libc_freeres_fn,\"axR\"" { target R_flag_in_section } } } */
diff --git a/gcc/varasm.c b/gcc/varasm.c
index c5487a78b13..e3e49d53e5d 100644
--- a/gcc/varasm.c
+++ b/gcc/varasm.c
@@ -281,7 +281,8 @@ get_noswitch_section (unsigned int flags, noswitch_section_callback callback)
 
 /* Return the named section structure associated with NAME.  Create
    a new section with the given fields if no such structure exists.
-   When NOT_EXISTING, then fail if the section already exists.  */
+   When NOT_EXISTING, then fail if the section already exists.  Return
+   the existing section if the SECTION_RETAIN bit doesn't match.  */
 
 section *
 get_section (const char *name, unsigned int flags, tree decl,
@@ -343,6 +344,11 @@ get_section (const char *name, unsigned int flags, tree decl,
 	      sect->common.flags |= (SECTION_WRITE | SECTION_RELRO);
 	      return sect;
 	    }
+	  /* If the SECTION_RETAIN bit doesn't match, return and switch
+	     to a new section later.  */
+	  if ((sect->common.flags & SECTION_RETAIN)
+	      != (flags & SECTION_RETAIN))
+	    return sect;
 	  /* Sanity check user variables for flag changes.  */
 	  if (sect->named.decl != NULL
 	      && DECL_P (sect->named.decl)
@@ -1879,7 +1885,7 @@ assemble_start_function (tree decl, const char *fnname)
 
   /* Switch to the correct text section for the start of the function.  */
 
-  switch_to_section (function_section (decl));
+  switch_to_section (function_section (decl), decl);
   if (crtl->has_bb_partition && !hot_label_written)
     ASM_OUTPUT_LABEL (asm_out_file, crtl->subsections.hot_section_label);
 
@@ -2375,7 +2381,7 @@ assemble_variable (tree decl, int top_level ATTRIBUTE_UNUSED,
 	  && (strcmp (sect->named.name, ".vtable_map_vars") == 0))
 	handle_vtv_comdat_section (sect, decl);
       else
-	switch_to_section (sect);
+	switch_to_section (sect, decl);
       if (align > BITS_PER_UNIT)
 	ASM_OUTPUT_ALIGN (asm_out_file, floor_log2 (align / BITS_PER_UNIT));
       assemble_variable_contents (decl, name, dont_output_data,
@@ -7742,10 +7748,28 @@ output_section_asm_op (const void *directive)
    the current section is NEW_SECTION.  */
 
 void
-switch_to_section (section *new_section)
+switch_to_section (section *new_section, tree decl)
 {
   if (in_section == new_section)
-    return;
+    {
+      if (HAVE_GAS_SHF_GNU_RETAIN
+	  && (new_section->common.flags & SECTION_NAMED)
+	  && decl != nullptr
+	  && DECL_P (decl)
+	  && (!!DECL_PRESERVE_P (decl)
+	      != !!(new_section->common.flags & SECTION_RETAIN)))
+	{
+	  /* If the SECTION_RETAIN bit doesn't match, switch to a new
+	     section.  */
+	  if (DECL_PRESERVE_P (decl))
+	    new_section->common.flags |= SECTION_RETAIN;
+	  else
+	    new_section->common.flags &= ~(SECTION_RETAIN
+					   | SECTION_DECLARED);
+	}
+      else
+	return;
+    }
 
   if (new_section->common.flags & SECTION_FORGET)
     in_section = NULL;
-- 
2.29.2

V4 [PATCH 2/3] Warn used and not used symbols in section with the same name

[H.J. Lu]

When SECTION_RETAIN is used, issue a warning when a symbol without used
attribute and a symbol with used attribute are placed in the section with
the same name, like

int __attribute__((used,section(".data.foo"))) foo2 = 2;
int __attribute__((section(".data.foo"))) foo1 = 1;

since assembler will put them in different sections with the same section
name.

gcc/

	PR target/98146
	* varasm.c (switch_to_section): Warn when a symbol without used
	attribute and a symbol with used attribute are placed in the
	section with the same name.

gcc/testsuite/

	PR target/98146
	* c-c++-common/attr-used-5.c: Updated.
	* c-c++-common/attr-used-6.c: Likewise.
	* c-c++-common/attr-used-7.c: Likewise.
	* c-c++-common/attr-used-8.c: Likewise.
---
 gcc/testsuite/c-c++-common/attr-used-5.c |  1 +
 gcc/testsuite/c-c++-common/attr-used-6.c |  1 +
 gcc/testsuite/c-c++-common/attr-used-7.c |  1 +
 gcc/testsuite/c-c++-common/attr-used-8.c |  1 +
 gcc/varasm.c                             | 22 +++++++++++++++++++---
 5 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/gcc/testsuite/c-c++-common/attr-used-5.c b/gcc/testsuite/c-c++-common/attr-used-5.c
index 9fc0d3834e9..ba59326e452 100644
--- a/gcc/testsuite/c-c++-common/attr-used-5.c
+++ b/gcc/testsuite/c-c++-common/attr-used-5.c
@@ -10,6 +10,7 @@ extern struct dtv_slotinfo_list *list;
 
 static int __attribute__ ((section ("__libc_freeres_fn")))
 free_slotinfo (struct dtv_slotinfo_list **elemp)
+/* { dg-warning "'.*' without 'used' attribute and '.*' with 'used' attribute are placed in a section with the same name" "" { target R_flag_in_section } .-1 } */
 {
   if (!free_slotinfo (&(*elemp)->next))
     return 0;
diff --git a/gcc/testsuite/c-c++-common/attr-used-6.c b/gcc/testsuite/c-c++-common/attr-used-6.c
index 0cb82ade5a9..5d20f875bf0 100644
--- a/gcc/testsuite/c-c++-common/attr-used-6.c
+++ b/gcc/testsuite/c-c++-common/attr-used-6.c
@@ -18,6 +18,7 @@ free_slotinfo (struct dtv_slotinfo_list **elemp)
 
 __attribute__ ((section ("__libc_freeres_fn")))
 void free_mem (void)
+/* { dg-warning "'.*' without 'used' attribute and '.*' with 'used' attribute are placed in a section with the same name" "" { target R_flag_in_section } .-1 } */
 {
   free_slotinfo (&list);
 }
diff --git a/gcc/testsuite/c-c++-common/attr-used-7.c b/gcc/testsuite/c-c++-common/attr-used-7.c
index fba2706ffc1..75576bcabe5 100644
--- a/gcc/testsuite/c-c++-common/attr-used-7.c
+++ b/gcc/testsuite/c-c++-common/attr-used-7.c
@@ -3,6 +3,7 @@
 
 int __attribute__((used,section(".data.foo"))) foo2 = 2;
 int __attribute__((section(".data.foo"))) foo1 = 1;
+/* { dg-warning "'.*' without 'used' attribute and '.*' with 'used' attribute are placed in a section with the same name" "" { target R_flag_in_section } .-1 } */
 
 /* { dg-final { scan-assembler ".data.foo,\"aw\"" { target R_flag_in_section } } } */
 /* { dg-final { scan-assembler ".data.foo,\"awR\"" { target R_flag_in_section } } } */
diff --git a/gcc/testsuite/c-c++-common/attr-used-8.c b/gcc/testsuite/c-c++-common/attr-used-8.c
index 4da4aabe573..e4982db1044 100644
--- a/gcc/testsuite/c-c++-common/attr-used-8.c
+++ b/gcc/testsuite/c-c++-common/attr-used-8.c
@@ -2,6 +2,7 @@
 /* { dg-options "-Wall -O2" } */
 
 int __attribute__((section(".data.foo"))) foo1 = 1;
+/* { dg-warning "'.*' without 'used' attribute and '.*' with 'used' attribute are placed in a section with the same name" "" { target R_flag_in_section } .-1 } */
 int __attribute__((used,section(".data.foo"))) foo2 = 2;
 
 /* { dg-final { scan-assembler ".data.foo,\"aw\"" { target R_flag_in_section } } } */
diff --git a/gcc/varasm.c b/gcc/varasm.c
index e3e49d53e5d..72d5379303a 100644
--- a/gcc/varasm.c
+++ b/gcc/varasm.c
@@ -7761,11 +7761,27 @@ switch_to_section (section *new_section, tree decl)
 	{
 	  /* If the SECTION_RETAIN bit doesn't match, switch to a new
 	     section.  */
+	  tree used_decl, no_used_decl;
+
 	  if (DECL_PRESERVE_P (decl))
-	    new_section->common.flags |= SECTION_RETAIN;
+	    {
+	      new_section->common.flags |= SECTION_RETAIN;
+	      used_decl = decl;
+	      no_used_decl = new_section->named.decl;
+	    }
 	  else
-	    new_section->common.flags &= ~(SECTION_RETAIN
-					   | SECTION_DECLARED);
+	    {
+	      new_section->common.flags &= ~(SECTION_RETAIN
+					     | SECTION_DECLARED);
+	      used_decl = new_section->named.decl;
+	      no_used_decl = decl;
+	    }
+	  warning (OPT_Wattributes,
+		   "%+qD without %<used%> attribute and %qD with "
+		   "%<used%> attribute are placed in a section with "
+		   "the same name", no_used_decl, used_decl);
+	  inform (DECL_SOURCE_LOCATION (used_decl),
+		  "%qD was declared here", used_decl);
 	}
       else
 	return;
-- 
2.29.2

V4 [PATCH 3/3] Require .init_array/.fini_array support for SHF_GNU_RETAIN

[H.J. Lu]

Since SHF_GNU_RETAIN support doesn't work for crtstuff.c which switches
the output section directly with asm statement:

---
static void __attribute__((used))
__do_global_dtors_aux (void)
{
  static _Bool completed;

  if (__builtin_expect (completed, 0))
    return;
  completed = 1;
}

static void __attribute__((__used__))
call___do_global_dtors_aux (void)
{
  asm ("\t.section\t.fini");
  __do_global_dtors_aux ();
  asm ("\t.section\t.text");
}
---

use SHF_GNU_RETAIN only if .init_array/.fini_array section is supported.

gcc/

	PR target/98146
	* defaults.h (SUPPORTS_SHF_GNU_RETAIN): New.
	* varasm.c (get_section): Replace HAVE_GAS_SHF_GNU_RETAIN with
	SUPPORTS_SHF_GNU_RETAIN.
	(resolve_unique_section): Likewise.
	(get_variable_section): Likewise.
	(switch_to_section): Likewise.

gcc/testsuite/

	PR target/98146
	* lib/target-supports.exp
	(check_effective_target_R_flag_in_section): Also check
	HAVE_INITFINI_ARRAY_SUPPORT != 0.
---
 gcc/defaults.h                        | 11 +++++++++++
 gcc/testsuite/lib/target-supports.exp |  2 +-
 gcc/varasm.c                          |  8 ++++----
 3 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/gcc/defaults.h b/gcc/defaults.h
index f1a38626624..80a84dde2d6 100644
--- a/gcc/defaults.h
+++ b/gcc/defaults.h
@@ -286,6 +286,17 @@ see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
 #endif
 #endif
 
+/* This determines whether or not we support marking sections with
+   SHF_GNU_RETAIN flag.  Also require .init_array/.fini_array section
+   for constructors and destructors.  */
+#ifndef SUPPORTS_SHF_GNU_RETAIN
+#if HAVE_GAS_SHF_GNU_RETAIN && HAVE_INITFINI_ARRAY_SUPPORT
+#define SUPPORTS_SHF_GNU_RETAIN 1
+#else
+#define SUPPORTS_SHF_GNU_RETAIN 0
+#endif
+#endif
+
 /* This determines whether or not we support link-once semantics.  */
 #ifndef SUPPORTS_ONE_ONLY
 #ifdef MAKE_DECL_ONE_ONLY
diff --git a/gcc/testsuite/lib/target-supports.exp b/gcc/testsuite/lib/target-supports.exp
index 3c02f763e7e..11343d0192f 100644
--- a/gcc/testsuite/lib/target-supports.exp
+++ b/gcc/testsuite/lib/target-supports.exp
@@ -10840,7 +10840,7 @@ proc check_effective_target_R_flag_in_section { } {
 
 	set f [open $src "w"]
 	puts $f "#include \"../../auto-host.h\""
-	puts $f "#if HAVE_GAS_SHF_GNU_RETAIN == 0"
+	puts $f "#if HAVE_GAS_SHF_GNU_RETAIN == 0 || HAVE_INITFINI_ARRAY_SUPPORT == 0"
 	puts $f "# error Assembler does not support 'R' flag in .section directive."
 	puts $f "#endif"
 	close $f
diff --git a/gcc/varasm.c b/gcc/varasm.c
index 72d5379303a..46f79ea28e6 100644
--- a/gcc/varasm.c
+++ b/gcc/varasm.c
@@ -293,7 +293,7 @@ get_section (const char *name, unsigned int flags, tree decl,
   slot = section_htab->find_slot_with_hash (name, htab_hash_string (name),
 					    INSERT);
   flags |= SECTION_NAMED;
-  if (HAVE_GAS_SHF_GNU_RETAIN
+  if (SUPPORTS_SHF_GNU_RETAIN
       && decl != nullptr
       && DECL_P (decl)
       && DECL_PRESERVE_P (decl))
@@ -483,7 +483,7 @@ resolve_unique_section (tree decl, int reloc ATTRIBUTE_UNUSED,
   if (DECL_SECTION_NAME (decl) == NULL
       && targetm_common.have_named_sections
       && (flag_function_or_data_sections
-	  || (HAVE_GAS_SHF_GNU_RETAIN && DECL_PRESERVE_P (decl))
+	  || (SUPPORTS_SHF_GNU_RETAIN && DECL_PRESERVE_P (decl))
 	  || DECL_COMDAT_GROUP (decl)))
     {
       targetm.asm_out.unique_section (decl, reloc);
@@ -1223,7 +1223,7 @@ get_variable_section (tree decl, bool prefer_noswitch_p)
     vnode->get_constructor ();
 
   if (DECL_COMMON (decl)
-      && !(HAVE_GAS_SHF_GNU_RETAIN && DECL_PRESERVE_P (decl)))
+      && !(SUPPORTS_SHF_GNU_RETAIN && DECL_PRESERVE_P (decl)))
     {
       /* If the decl has been given an explicit section name, or it resides
 	 in a non-generic address space, then it isn't common, and shouldn't
@@ -7752,7 +7752,7 @@ switch_to_section (section *new_section, tree decl)
 {
   if (in_section == new_section)
     {
-      if (HAVE_GAS_SHF_GNU_RETAIN
+      if (SUPPORTS_SHF_GNU_RETAIN
 	  && (new_section->common.flags & SECTION_NAMED)
 	  && decl != nullptr
 	  && DECL_P (decl)
-- 
2.29.2

Re: V4 [PATCH 1/3] Switch to a new section if the SECTION_RETAIN bit doesn't match

[Jeff Law]

On 12/15/20 10:30 AM, H.J. Lu wrote:
> When definitions marked with used attribute and unmarked definitions are
> placed in the section with the same name, switch to a new section if the
> SECTION_RETAIN bit doesn't match.
>
> gcc/
>
> 	PR target/98146
> 	* output.h (switch_to_section): Add a tree argument, default to
> 	nullptr.
> 	* varasm.c (get_section): If the SECTION_RETAIN bit doesn't match,
> 	return and switch to a new section later.
> 	(assemble_start_function): Pass decl to switch_to_section.
> 	(assemble_variable): Likewise.
> 	(switch_to_section): If the SECTION_RETAIN bit doesn't match,
> 	switch to a new section.
>
> gcc/testsuite/
>
> 	PR target/98146
> 	* c-c++-common/attr-used-5.c: New test.
> 	* c-c++-common/attr-used-6.c: Likewise.
> 	* c-c++-common/attr-used-7.c: Likewise.
> 	* c-c++-common/attr-used-8.c: Likewise.
> 	* c-c++-common/attr-used-9.c: Likewise.
So as an additional follow-up could you add to the get_section comment
the special handling were add SECTION_WRITE and SECTION_RELRO to the
flags.  That's not something I would expect that function to do either. 
Consider that comment addition pre-approved.

Jeff

Re: V4 [PATCH 2/3] Warn used and not used symbols in section with the same name

[Jeff Law]

On 12/15/20 10:30 AM, H.J. Lu wrote:
> When SECTION_RETAIN is used, issue a warning when a symbol without used
> attribute and a symbol with used attribute are placed in the section with
> the same name, like
>
> int __attribute__((used,section(".data.foo"))) foo2 = 2;
> int __attribute__((section(".data.foo"))) foo1 = 1;
>
> since assembler will put them in different sections with the same section
> name.
>
> gcc/
>
> 	PR target/98146
> 	* varasm.c (switch_to_section): Warn when a symbol without used
> 	attribute and a symbol with used attribute are placed in the
> 	section with the same name.
>
> gcc/testsuite/
>
> 	PR target/98146
> 	* c-c++-common/attr-used-5.c: Updated.
> 	* c-c++-common/attr-used-6.c: Likewise.
> 	* c-c++-common/attr-used-7.c: Likewise.
> 	* c-c++-common/attr-used-8.c: Likewise.
OK
jeff

Re: V4 [PATCH 3/3] Require .init_array/.fini_array support for SHF_GNU_RETAIN

[Jeff Law]

On 12/15/20 10:30 AM, H.J. Lu wrote:
> Since SHF_GNU_RETAIN support doesn't work for crtstuff.c which switches
> the output section directly with asm statement:
>
> ---
> static void __attribute__((used))
> __do_global_dtors_aux (void)
> {
>   static _Bool completed;
>
>   if (__builtin_expect (completed, 0))
>     return;
>   completed = 1;
> }
>
> static void __attribute__((__used__))
> call___do_global_dtors_aux (void)
> {
>   asm ("\t.section\t.fini");
>   __do_global_dtors_aux ();
>   asm ("\t.section\t.text");
> }
> ---
>
> use SHF_GNU_RETAIN only if .init_array/.fini_array section is supported.
>
> gcc/
>
> 	PR target/98146
> 	* defaults.h (SUPPORTS_SHF_GNU_RETAIN): New.
> 	* varasm.c (get_section): Replace HAVE_GAS_SHF_GNU_RETAIN with
> 	SUPPORTS_SHF_GNU_RETAIN.
> 	(resolve_unique_section): Likewise.
> 	(get_variable_section): Likewise.
> 	(switch_to_section): Likewise.
>
> gcc/testsuite/
>
> 	PR target/98146
> 	* lib/target-supports.exp
> 	(check_effective_target_R_flag_in_section): Also check
> 	HAVE_INITFINI_ARRAY_SUPPORT != 0.
Ah.  I didn't realize that you added this to the V4 patch.  OK.

jeff

Re: V4 [PATCH 1/3] Switch to a new section if the SECTION_RETAIN bit doesn't match

[H.J. Lu]

[-- Attachment #1: Type: text/plain, Size: 2345 bytes --]

On Tue, Dec 15, 2020 at 4:44 PM Jeff Law <law@redhat.com> wrote:
>
>
>
> On 12/15/20 10:30 AM, H.J. Lu wrote:
> > When definitions marked with used attribute and unmarked definitions are
> > placed in the section with the same name, switch to a new section if the
> > SECTION_RETAIN bit doesn't match.
> >
> > gcc/
> >
> >       PR target/98146
> >       * output.h (switch_to_section): Add a tree argument, default to
> >       nullptr.
> >       * varasm.c (get_section): If the SECTION_RETAIN bit doesn't match,
> >       return and switch to a new section later.
> >       (assemble_start_function): Pass decl to switch_to_section.
> >       (assemble_variable): Likewise.
> >       (switch_to_section): If the SECTION_RETAIN bit doesn't match,
> >       switch to a new section.
> >
> > gcc/testsuite/
> >
> >       PR target/98146
> >       * c-c++-common/attr-used-5.c: New test.
> >       * c-c++-common/attr-used-6.c: Likewise.
> >       * c-c++-common/attr-used-7.c: Likewise.
> >       * c-c++-common/attr-used-8.c: Likewise.
> >       * c-c++-common/attr-used-9.c: Likewise.
> So as an additional follow-up could you add to the get_section comment
> the special handling were add SECTION_WRITE and SECTION_RELRO to the
> flags.  That's not something I would expect that function to do either.
> Consider that comment addition pre-approved.
>

I am checking the patch with this change:

diff --git a/gcc/varasm.c b/gcc/varasm.c
index 46f79ea28e6..267a052331d 100644
--- a/gcc/varasm.c
+++ b/gcc/varasm.c
@@ -282,7 +282,11 @@ get_noswitch_section (unsigned int flags,
noswitch_section_callback callback)
 /* Return the named section structure associated with NAME.  Create
    a new section with the given fields if no such structure exists.
    When NOT_EXISTING, then fail if the section already exists.  Return
-   the existing section if the SECTION_RETAIN bit doesn't match.  */
+   the existing section if the SECTION_RETAIN bit doesn't match.  Set
+   the SECTION_WRITE | SECTION_RELRO bits on the the existing section
+   if one of the section flags is SECTION_WRITE | SECTION_RELRO and the
+   other has none of these flags in named sections and either the section
+   hasn't been declared yet or has been declared as writable.  */

 section *
 get_section (const char *name, unsigned int flags, tree decl,

Thanks.

-- 
H.J.

[-- Attachment #2: 0001-Switch-to-a-new-section-if-the-SECTION_RETAIN-bit-do.patch --]
[-- Type: text/x-patch, Size: 9429 bytes --]

From 22c1d0be1399becffac58d7509ab30a8ecd97a9a Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <hjl.tools@gmail.com>
Date: Thu, 3 Dec 2020 11:01:06 -0800
Subject: [PATCH] Switch to a new section if the SECTION_RETAIN bit doesn't
 match

When definitions marked with used attribute and unmarked definitions are
placed in the section with the same name, switch to a new section if the
SECTION_RETAIN bit doesn't match.

gcc/

	PR target/98146
	* output.h (switch_to_section): Add a tree argument, default to
	nullptr.
	* varasm.c (get_section): If the SECTION_RETAIN bit doesn't match,
	return and switch to a new section later.
	(assemble_start_function): Pass decl to switch_to_section.
	(assemble_variable): Likewise.
	(switch_to_section): If the SECTION_RETAIN bit doesn't match,
	switch to a new section.

gcc/testsuite/

	PR target/98146
	* c-c++-common/attr-used-5.c: New test.
	* c-c++-common/attr-used-6.c: Likewise.
	* c-c++-common/attr-used-7.c: Likewise.
	* c-c++-common/attr-used-8.c: Likewise.
	* c-c++-common/attr-used-9.c: Likewise.
---
 gcc/output.h                             |  2 +-
 gcc/testsuite/c-c++-common/attr-used-5.c | 26 ++++++++++++++++
 gcc/testsuite/c-c++-common/attr-used-6.c | 26 ++++++++++++++++
 gcc/testsuite/c-c++-common/attr-used-7.c |  8 +++++
 gcc/testsuite/c-c++-common/attr-used-8.c |  8 +++++
 gcc/testsuite/c-c++-common/attr-used-9.c | 28 +++++++++++++++++
 gcc/varasm.c                             | 38 ++++++++++++++++++++----
 7 files changed, 130 insertions(+), 6 deletions(-)
 create mode 100644 gcc/testsuite/c-c++-common/attr-used-5.c
 create mode 100644 gcc/testsuite/c-c++-common/attr-used-6.c
 create mode 100644 gcc/testsuite/c-c++-common/attr-used-7.c
 create mode 100644 gcc/testsuite/c-c++-common/attr-used-8.c
 create mode 100644 gcc/testsuite/c-c++-common/attr-used-9.c

diff --git a/gcc/output.h b/gcc/output.h
index fa8ace1f394..1f9af46da1d 100644
--- a/gcc/output.h
+++ b/gcc/output.h
@@ -548,7 +548,7 @@ extern void switch_to_other_text_partition (void);
 extern section *get_cdtor_priority_section (int, bool);
 
 extern bool unlikely_text_section_p (section *);
-extern void switch_to_section (section *);
+extern void switch_to_section (section *, tree = nullptr);
 extern void output_section_asm_op (const void *);
 
 extern void record_tm_clone_pair (tree, tree);
diff --git a/gcc/testsuite/c-c++-common/attr-used-5.c b/gcc/testsuite/c-c++-common/attr-used-5.c
new file mode 100644
index 00000000000..9fc0d3834e9
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/attr-used-5.c
@@ -0,0 +1,26 @@
+/* { dg-do compile } */
+/* { dg-options "-Wall -O2" } */
+
+struct dtv_slotinfo_list
+{
+  struct dtv_slotinfo_list *next;
+};
+
+extern struct dtv_slotinfo_list *list;
+
+static int __attribute__ ((section ("__libc_freeres_fn")))
+free_slotinfo (struct dtv_slotinfo_list **elemp)
+{
+  if (!free_slotinfo (&(*elemp)->next))
+    return 0;
+  return 1;
+}
+
+__attribute__ ((used, section ("__libc_freeres_fn")))
+static void free_mem (void)
+{
+  free_slotinfo (&list);
+}
+
+/* { dg-final { scan-assembler "__libc_freeres_fn,\"ax\"" { target R_flag_in_section } } } */
+/* { dg-final { scan-assembler "__libc_freeres_fn,\"axR\"" { target R_flag_in_section } } } */
diff --git a/gcc/testsuite/c-c++-common/attr-used-6.c b/gcc/testsuite/c-c++-common/attr-used-6.c
new file mode 100644
index 00000000000..0cb82ade5a9
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/attr-used-6.c
@@ -0,0 +1,26 @@
+/* { dg-do compile } */
+/* { dg-options "-Wall -O2" } */
+
+struct dtv_slotinfo_list
+{
+  struct dtv_slotinfo_list *next;
+};
+
+extern struct dtv_slotinfo_list *list;
+
+static int __attribute__ ((used, section ("__libc_freeres_fn")))
+free_slotinfo (struct dtv_slotinfo_list **elemp)
+{
+  if (!free_slotinfo (&(*elemp)->next))
+    return 0;
+  return 1;
+}
+
+__attribute__ ((section ("__libc_freeres_fn")))
+void free_mem (void)
+{
+  free_slotinfo (&list);
+}
+
+/* { dg-final { scan-assembler "__libc_freeres_fn,\"ax\"" { target R_flag_in_section } } } */
+/* { dg-final { scan-assembler "__libc_freeres_fn,\"axR\"" { target R_flag_in_section } } } */
diff --git a/gcc/testsuite/c-c++-common/attr-used-7.c b/gcc/testsuite/c-c++-common/attr-used-7.c
new file mode 100644
index 00000000000..fba2706ffc1
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/attr-used-7.c
@@ -0,0 +1,8 @@
+/* { dg-do compile } */
+/* { dg-options "-Wall -O2" } */
+
+int __attribute__((used,section(".data.foo"))) foo2 = 2;
+int __attribute__((section(".data.foo"))) foo1 = 1;
+
+/* { dg-final { scan-assembler ".data.foo,\"aw\"" { target R_flag_in_section } } } */
+/* { dg-final { scan-assembler ".data.foo,\"awR\"" { target R_flag_in_section } } } */
diff --git a/gcc/testsuite/c-c++-common/attr-used-8.c b/gcc/testsuite/c-c++-common/attr-used-8.c
new file mode 100644
index 00000000000..4da4aabe573
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/attr-used-8.c
@@ -0,0 +1,8 @@
+/* { dg-do compile } */
+/* { dg-options "-Wall -O2" } */
+
+int __attribute__((section(".data.foo"))) foo1 = 1;
+int __attribute__((used,section(".data.foo"))) foo2 = 2;
+
+/* { dg-final { scan-assembler ".data.foo,\"aw\"" { target R_flag_in_section } } } */
+/* { dg-final { scan-assembler ".data.foo,\"awR\"" { target R_flag_in_section } } } */
diff --git a/gcc/testsuite/c-c++-common/attr-used-9.c b/gcc/testsuite/c-c++-common/attr-used-9.c
new file mode 100644
index 00000000000..cf3bde67622
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/attr-used-9.c
@@ -0,0 +1,28 @@
+/* { dg-do compile } */
+/* { dg-options "-Wall -O2" } */
+
+struct dtv_slotinfo_list
+{
+  struct dtv_slotinfo_list *next;
+};
+
+extern struct dtv_slotinfo_list *list;
+
+static int __attribute__ ((used, section ("__libc_freeres_fn")))
+free_slotinfo (struct dtv_slotinfo_list **elemp)
+{
+  if (!free_slotinfo (&(*elemp)->next))
+    return 0;
+  return 1;
+}
+
+__attribute__ ((section ("__libc_freeres_fn")))
+static void free_mem (void)
+/* { dg-warning "defined but not used" "" { target *-*-* } .-1 } */
+{
+  free_slotinfo (&list);
+}
+
+/* { dg-final { scan-assembler-not "__libc_freeres_fn\n" } } */
+/* { dg-final { scan-assembler-not "__libc_freeres_fn,\"ax\"" { target R_flag_in_section } } } */
+/* { dg-final { scan-assembler "__libc_freeres_fn,\"axR\"" { target R_flag_in_section } } } */
diff --git a/gcc/varasm.c b/gcc/varasm.c
index c5487a78b13..cfec870e067 100644
--- a/gcc/varasm.c
+++ b/gcc/varasm.c
@@ -281,7 +281,12 @@ get_noswitch_section (unsigned int flags, noswitch_section_callback callback)
 
 /* Return the named section structure associated with NAME.  Create
    a new section with the given fields if no such structure exists.
-   When NOT_EXISTING, then fail if the section already exists.  */
+   When NOT_EXISTING, then fail if the section already exists.  Return
+   the existing section if the SECTION_RETAIN bit doesn't match.  Set
+   the SECTION_WRITE | SECTION_RELRO bits on the the existing section
+   if one of the section flags is SECTION_WRITE | SECTION_RELRO and the
+   other has none of these flags in named sections and either the section
+   hasn't been declared yet or has been declared as writable.  */
 
 section *
 get_section (const char *name, unsigned int flags, tree decl,
@@ -343,6 +348,11 @@ get_section (const char *name, unsigned int flags, tree decl,
 	      sect->common.flags |= (SECTION_WRITE | SECTION_RELRO);
 	      return sect;
 	    }
+	  /* If the SECTION_RETAIN bit doesn't match, return and switch
+	     to a new section later.  */
+	  if ((sect->common.flags & SECTION_RETAIN)
+	      != (flags & SECTION_RETAIN))
+	    return sect;
 	  /* Sanity check user variables for flag changes.  */
 	  if (sect->named.decl != NULL
 	      && DECL_P (sect->named.decl)
@@ -1879,7 +1889,7 @@ assemble_start_function (tree decl, const char *fnname)
 
   /* Switch to the correct text section for the start of the function.  */
 
-  switch_to_section (function_section (decl));
+  switch_to_section (function_section (decl), decl);
   if (crtl->has_bb_partition && !hot_label_written)
     ASM_OUTPUT_LABEL (asm_out_file, crtl->subsections.hot_section_label);
 
@@ -2375,7 +2385,7 @@ assemble_variable (tree decl, int top_level ATTRIBUTE_UNUSED,
 	  && (strcmp (sect->named.name, ".vtable_map_vars") == 0))
 	handle_vtv_comdat_section (sect, decl);
       else
-	switch_to_section (sect);
+	switch_to_section (sect, decl);
       if (align > BITS_PER_UNIT)
 	ASM_OUTPUT_ALIGN (asm_out_file, floor_log2 (align / BITS_PER_UNIT));
       assemble_variable_contents (decl, name, dont_output_data,
@@ -7742,10 +7752,28 @@ output_section_asm_op (const void *directive)
    the current section is NEW_SECTION.  */
 
 void
-switch_to_section (section *new_section)
+switch_to_section (section *new_section, tree decl)
 {
   if (in_section == new_section)
-    return;
+    {
+      if (HAVE_GAS_SHF_GNU_RETAIN
+	  && (new_section->common.flags & SECTION_NAMED)
+	  && decl != nullptr
+	  && DECL_P (decl)
+	  && (!!DECL_PRESERVE_P (decl)
+	      != !!(new_section->common.flags & SECTION_RETAIN)))
+	{
+	  /* If the SECTION_RETAIN bit doesn't match, switch to a new
+	     section.  */
+	  if (DECL_PRESERVE_P (decl))
+	    new_section->common.flags |= SECTION_RETAIN;
+	  else
+	    new_section->common.flags &= ~(SECTION_RETAIN
+					   | SECTION_DECLARED);
+	}
+      else
+	return;
+    }
 
   if (new_section->common.flags & SECTION_FORGET)
     in_section = NULL;
-- 
2.29.2