[gcc r11-6140] Switch to a new section if the SECTION_RETAIN bit doesn't match

[gcc r11-6140] Switch to a new section if the SECTION_RETAIN bit doesn't match

[H.J. Lu]

https://gcc.gnu.org/g:6175383249143309fdc780a02bea484f4450def7

commit r11-6140-g6175383249143309fdc780a02bea484f4450def7
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Thu Dec 3 11:01:06 2020 -0800

    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.

Diff:
---
 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(-)

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;