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

["H.J. Lu" <hjl.tools@gmail.com>]

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