Support SHF_GNU_RETAIN ELF section flag

The SHF_GNU_RETAIN section flag is an extension to the GNU ELF OSABI.
It is defined as follows:

=========================================================
Section Attribute Flags
+-------------------------------------+
| Name           | Value              |
+-------------------------------------+
| SHF_GNU_RETAIN | 0x200000 (1 << 21) |
+-------------------------------------+

SHF_GNU_RETAIN
  The link editor should not garbage collect the section.
=========================================================

The .section directive accepts the "R" flag, which indicates
SHF_GNU_RETAIN should be applied to the section.

There is not a direct mapping of SHF_GNU_RETAIN to the BFD
section flag SEC_KEEP. Keeping these flags distinct allows
SHF_GNU_RETAIN sections to be explicitly removed by placing them in
/DISCARD/.

bfd/ChangeLog:

	* elf-bfd.h (enum elf_gnu_osabi): Add elf_gnu_osabi_retain.
	(struct elf_obj_tdata): Increase has_gnu_osabi to 4 bits.
	* elf.c (_bfd_elf_make_section_from_shdr): Set elf_gnu_osabi_retain
	for SHF_GNU_RETAIN.
	(_bfd_elf_final_write_processing): Report if SHF_GNU_RETAIN is
	not supported by the OSABI.
	Adjust error messages.
	* elflink.c (elf_link_input_bfd): Copy enabled has_gnu_osabi bits from
	input BFD to output BFD.
	(bfd_elf_gc_sections): gc_mark the section if SHF_GNU_RETAIN is set.

binutils/ChangeLog:

	* NEWS: Announce SHF_GNU_RETAIN support.
	* readelf.c (get_elf_section_flags): Handle SHF_GNU_RETAIN.
	Recognize SHF_GNU_RETAIN and SHF_GNU_MBIND only for supported OSABIs.
	* testsuite/binutils-all/readelf.exp: Run new tests.
	Don't run run_dump_test when there isn't an assembler available.
	* testsuite/lib/binutils-common.exp (supports_gnu_osabi): Adjust
	comment.
	* testsuite/binutils-all/readelf-maskos-1a.d: New test.
	* testsuite/binutils-all/readelf-maskos-1b.d: New test.
	* testsuite/binutils-all/readelf-maskos.s: New test.
	* testsuite/binutils-all/retain1.s: New test.
	* testsuite/binutils-all/retain1a.d: New test.
	* testsuite/binutils-all/retain1b.d: New test.

gas/ChangeLog:

	* NEWS: Announce SHF_GNU_RETAIN support.
	* config/obj-elf.c (obj_elf_change_section): Merge SHF_GNU_RETAIN bit
	between section declarations.
	(obj_elf_parse_section_letters): Handle 'R' flag.
	Handle numeric flag values within the SHF_MASKOS range.
	(obj_elf_section): Validate SHF_GNU_RETAIN usage.
	* doc/as.texi: Document 'R' flag to .section directive.
	* testsuite/gas/elf/elf.exp: Run new tests.
	* testsuite/gas/elf/section10.d: Unset SHF_GNU_RETAIN bit.
	* testsuite/gas/elf/section10.s: Likewise.
	* testsuite/gas/elf/section22.d: New test.
	* testsuite/gas/elf/section22.s: New test.
	* testsuite/gas/elf/section23.s: New test.
	* testsuite/gas/elf/section23a.d: New test.
	* testsuite/gas/elf/section23b.d: New test.
	* testsuite/gas/elf/section23b.err: New test.
	* testsuite/gas/elf/section24.l: New test.
	* testsuite/gas/elf/section24.s: New test.
	* testsuite/gas/elf/section24a.d: New test.
	* testsuite/gas/elf/section24b.d: New test.

include/ChangeLog:

	* elf/common.h (SHF_GNU_RETAIN): Define.

ld/ChangeLog:

	* NEWS: Announce support for SHF_GNU_RETAIN.
	* ld.texi (garbage collection): Document SHF_GNU_RETAIN.
	(Output Section Discarding): Likewise.
	* testsuite/ld-elf/elf.exp: Run new tests.
	* testsuite/ld-elf/retain1.s: New test.
	* testsuite/ld-elf/retain1a.d: New test.
	* testsuite/ld-elf/retain1b.d: New test.
	* testsuite/ld-elf/retain2.d: New test.
	* testsuite/ld-elf/retain2.ld: New test.
	* testsuite/ld-elf/retain2.map: New test.
	* testsuite/ld-elf/retain3.d: New test.
	* testsuite/ld-elf/retain3.s: New test.
	* testsuite/ld-elf/retain4.d: New test.
	* testsuite/ld-elf/retain4.s: New test.
	* testsuite/ld-elf/retain5.d: New test.
	* testsuite/ld-elf/retain5.map: New test.
	* testsuite/ld-elf/retain5lib.s: New test.
	* testsuite/ld-elf/retain5main.s: New test.
	* testsuite/ld-elf/retain6a.d: New test.
	* testsuite/ld-elf/retain6b.d: New test.
	* testsuite/ld-elf/retain6lib.s: New test.
	* testsuite/ld-elf/retain6main.s: New test.

11 files changed, 280 insertions, 8 deletions

diff --git a/binutils/ChangeLog b/binutils/ChangeLog
index 2124c59..e8bcd97 100644
--- a/binutils/ChangeLog
+++ b/binutils/ChangeLog
@@ -1,3 +1,19 @@
+2020-11-18  Jozef Lawrynowicz  <jozef.l@mittosystems.com>
+
+	* NEWS: Announce SHF_GNU_RETAIN support.
+	* readelf.c (get_elf_section_flags): Handle SHF_GNU_RETAIN.
+	Recognize SHF_GNU_RETAIN and SHF_GNU_MBIND only for supported OSABIs.
+	* testsuite/binutils-all/readelf.exp: Run new tests.
+	Don't run run_dump_test when there isn't an assembler available.
+	* testsuite/lib/binutils-common.exp (supports_gnu_osabi): Adjust
+	comment.
+	* testsuite/binutils-all/readelf-maskos-1a.d: New test.
+	* testsuite/binutils-all/readelf-maskos-1b.d: New test.
+	* testsuite/binutils-all/readelf-maskos.s: New test.
+	* testsuite/binutils-all/retain1.s: New test.
+	* testsuite/binutils-all/retain1a.d: New test.
+	* testsuite/binutils-all/retain1b.d: New test.
+
 2020-11-17  Howard Chu  <hyc@symas.com>
 
 	* ar.c (main): Place the libdeps record in the second archive
diff --git a/binutils/NEWS b/binutils/NEWS
index 02a19ea..e74b6a2 100644
--- a/binutils/NEWS
+++ b/binutils/NEWS
@@ -12,6 +12,10 @@
   symbol names.  In addition the --demangle=<style>, --no-demangle,
   --recurse-limit and --no-recurse-limit options are also now availale.
 
+* Add support for the SHF_GNU_RETAIN ELF section flag.
+  This flag specifies that the section should not be garbage collected by the
+  linker.
+
 Changes in 2.35:
 
 * Changed readelf's display of symbol names when wide mode is not enabled.
diff --git a/binutils/readelf.c b/binutils/readelf.c
index 6373852..f6a074b 100644
--- a/binutils/readelf.c
+++ b/binutils/readelf.c
@@ -5996,6 +5996,8 @@ get_elf_section_flags (Filedata * filedata, bfd_vma sh_flags)
       /* 24 */ { STRING_COMMA_LEN ("GNU_MBIND") },
       /* VLE specific.  */
       /* 25 */ { STRING_COMMA_LEN ("VLE") },
+      /* GNU specific.  */
+      /* 26 */ { STRING_COMMA_LEN ("GNU_RETAIN") },
     };
 
   if (do_section_details)
@@ -6028,7 +6030,6 @@ get_elf_section_flags (Filedata * filedata, bfd_vma sh_flags)
 	    case SHF_TLS:		sindex = 9; break;
 	    case SHF_EXCLUDE:		sindex = 18; break;
 	    case SHF_COMPRESSED:	sindex = 20; break;
-	    case SHF_GNU_MBIND:		sindex = 24; break;
 
 	    default:
 	      sindex = -1;
@@ -6080,10 +6081,28 @@ get_elf_section_flags (Filedata * filedata, bfd_vma sh_flags)
 		  if (flag == SHF_PPC_VLE)
 		    sindex = 25;
 		  break;
+		default:
+		  break;
+		}
 
+	      switch (filedata->file_header.e_ident[EI_OSABI])
+		{
+		case ELFOSABI_GNU:
+		case ELFOSABI_FREEBSD:
+		  if (flag == SHF_GNU_RETAIN)
+		    sindex = 26;
+		  /* Fall through */
+		case ELFOSABI_NONE:
+		  if (flag == SHF_GNU_MBIND)
+		    /* We should not recognize SHF_GNU_MBIND for
+		       ELFOSABI_NONE, but binutils as of 2019-07-23 did
+		       not set the EI_OSABI header byte.  */
+		    sindex = 24;
+		  break;
 		default:
 		  break;
 		}
+	      break;
 	    }
 
 	  if (sindex != -1)
@@ -6126,7 +6145,6 @@ get_elf_section_flags (Filedata * filedata, bfd_vma sh_flags)
 	    case SHF_TLS:		*p = 'T'; break;
 	    case SHF_EXCLUDE:		*p = 'E'; break;
 	    case SHF_COMPRESSED:	*p = 'C'; break;
-	    case SHF_GNU_MBIND:		*p = 'D'; break;
 
 	    default:
 	      if ((filedata->file_header.e_machine == EM_X86_64
@@ -6136,14 +6154,37 @@ get_elf_section_flags (Filedata * filedata, bfd_vma sh_flags)
 		*p = 'l';
 	      else if (filedata->file_header.e_machine == EM_ARM
 		       && flag == SHF_ARM_PURECODE)
-		  *p = 'y';
+		*p = 'y';
 	      else if (filedata->file_header.e_machine == EM_PPC
 		       && flag == SHF_PPC_VLE)
-		  *p = 'v';
+		*p = 'v';
 	      else if (flag & SHF_MASKOS)
 		{
-		  *p = 'o';
-		  sh_flags &= ~ SHF_MASKOS;
+		  switch (filedata->file_header.e_ident[EI_OSABI])
+		    {
+		    case ELFOSABI_GNU:
+		    case ELFOSABI_FREEBSD:
+		      if (flag == SHF_GNU_RETAIN)
+			{
+			  *p = 'R';
+			  break;
+			}
+		      /* Fall through */
+		    case ELFOSABI_NONE:
+		      if (flag == SHF_GNU_MBIND)
+			{
+			  /* We should not recognize SHF_GNU_MBIND for
+			     ELFOSABI_NONE, but binutils as of 2019-07-23 did
+			     not set the EI_OSABI header byte.  */
+			  *p = 'D';
+			  break;
+			}
+		      /* Fall through */
+		    default:
+		      *p = 'o';
+		      sh_flags &= ~SHF_MASKOS;
+		      break;
+		    }
 		}
 	      else if (flag & SHF_MASKPROC)
 		{
diff --git a/binutils/testsuite/binutils-all/readelf-maskos-1a.d b/binutils/testsuite/binutils-all/readelf-maskos-1a.d
new file mode 100644
index 0000000..7b27358
--- /dev/null
+++ b/binutils/testsuite/binutils-all/readelf-maskos-1a.d
@@ -0,0 +1,10 @@
+#name: Unknown SHF_MASKOS value in section
+#source: readelf-maskos.s
+#notarget: [supports_gnu_osabi] msp430-*-elf visium-*-elf
+#xfail: arm-*-elf
+#readelf: -S --wide
+# PR26722 for the arm-*-elf XFAIL
+
+#...
+  \[[ 0-9]+\] .data.retain_var.*WAo.*
+#pass
diff --git a/binutils/testsuite/binutils-all/readelf-maskos-1b.d b/binutils/testsuite/binutils-all/readelf-maskos-1b.d
new file mode 100644
index 0000000..2cbb58a
--- /dev/null
+++ b/binutils/testsuite/binutils-all/readelf-maskos-1b.d
@@ -0,0 +1,12 @@
+#name: -t (section details) for unknown SHF_MASKOS value in section
+#source: readelf-maskos.s
+#notarget: [supports_gnu_osabi] msp430-*-elf visium-*-elf
+#xfail: arm-*-elf
+#readelf: -S -t --wide
+# PR26722 for the arm-*-elf XFAIL
+
+#...
+  \[[ 0-9]+\] .data.retain_var
+       PROGBITS +0+ +[0-9a-f]+ +[0-9a-f]+ +[0-9a-f]+ +0 +0 +(1|2|4|8)
+       \[00200003\]: WRITE, ALLOC, OS \(00200000\)
+#pass
diff --git a/binutils/testsuite/binutils-all/readelf-maskos.s b/binutils/testsuite/binutils-all/readelf-maskos.s
new file mode 100644
index 0000000..d671119
--- /dev/null
+++ b/binutils/testsuite/binutils-all/readelf-maskos.s
@@ -0,0 +1,11 @@
+  .section	.data.retain_var,"0x200003"
+	.global	retain_var
+	.type	retain_var, %object
+retain_var:
+	.long	2
+
+	.section	.text._start,"ax"
+	.global	_start
+	.type	_start, %function
+_start:
+	.word 0
diff --git a/binutils/testsuite/binutils-all/readelf.exp b/binutils/testsuite/binutils-all/readelf.exp
index 1fb36ae..9d1d496 100644
--- a/binutils/testsuite/binutils-all/readelf.exp
+++ b/binutils/testsuite/binutils-all/readelf.exp
@@ -364,8 +364,15 @@ readelf_wi_test
 readelf_compressed_wa_test
 
 readelf_dump_test
-run_dump_test "pr25543"
 
+# These dump tests require an assembler.
+if {[which $AS] != 0} then {
+    run_dump_test "pr25543"
+    run_dump_test "retain1a"
+    run_dump_test "retain1b"
+    run_dump_test "readelf-maskos-1a"
+    run_dump_test "readelf-maskos-1b"
+}
 
 # PR 13482 - Check for off-by-one errors when dumping .note sections.
 if {![binutils_assemble $srcdir/$subdir/version.s tmpdir/version.o]} then {
diff --git a/binutils/testsuite/binutils-all/retain1.s b/binutils/testsuite/binutils-all/retain1.s
new file mode 100644
index 0000000..f7716fa
--- /dev/null
+++ b/binutils/testsuite/binutils-all/retain1.s
@@ -0,0 +1,104 @@
+	.global	discard0
+	.section	.bss.discard0,"aw"
+	.type	discard0, %object
+discard0:
+	.zero	2
+
+	.global	discard1
+	.section	.bss.discard1,"aw"
+	.type	discard1, %object
+discard1:
+	.zero	2
+
+	.global	discard2
+	.section	.data.discard2,"aw"
+	.type	discard2, %object
+discard2:
+	.word	1
+
+	.section	.bss.sdiscard0,"aw"
+	.type	sdiscard0, %object
+sdiscard0:
+	.zero	2
+
+	.section	.bss.sdiscard1,"aw"
+	.type	sdiscard1, %object
+sdiscard1:
+	.zero	2
+
+	.section	.data.sdiscard2,"aw"
+	.type	sdiscard2, %object
+sdiscard2:
+	.word	1
+
+	.section	.text.fndiscard0,"ax"
+	.global	fndiscard0
+	.type	fndiscard0, %function
+fndiscard0:
+	.word 0
+
+	.global	retain0
+	.section	.bss.retain0,"awR"
+	.type	retain0, %object
+retain0:
+	.zero	2
+
+	.global	retain1
+	.section	.bss.retain1,"awR"
+	.type	retain1, %object
+retain1:
+	.zero	2
+
+	.global	retain2
+	.section	.data.retain2,"awR"
+	.type	retain2, %object
+retain2:
+	.word	1
+
+	.section	.bss.sretain0,"awR"
+	.type	sretain0, %object
+sretain0:
+	.zero	2
+
+	.section	.bss.sretain1,"awR"
+	.type	sretain1, %object
+sretain1:
+	.zero	2
+
+	.section	.data.sretain2,"aRw"
+	.type	sretain2, %object
+sretain2:
+	.word	1
+
+	.section	.text.fnretain1,"Rax"
+	.global	fnretain1
+	.type	fnretain1, %function
+fnretain1:
+	.word	0
+
+	.section	.text.fndiscard2,"ax"
+	.global	fndiscard2
+	.type	fndiscard2, %function
+fndiscard2:
+	.word	0
+
+	.section	.bss.lsretain0,"awR"
+	.type	lsretain0.2, %object
+lsretain0.2:
+	.zero	2
+
+	.section	.bss.lsretain1,"aRw"
+	.type	lsretain1.1, %object
+lsretain1.1:
+	.zero	2
+
+	.section	.data.lsretain2,"aRw"
+	.type	lsretain2.0, %object
+lsretain2.0:
+	.word	1
+
+	.section	.text._start,"ax"
+	.global	_start
+	.type	_start, %function
+_start:
+	.word 0
diff --git a/binutils/testsuite/binutils-all/retain1a.d b/binutils/testsuite/binutils-all/retain1a.d
new file mode 100644
index 0000000..6397ac5
--- /dev/null
+++ b/binutils/testsuite/binutils-all/retain1a.d
@@ -0,0 +1,18 @@
+#name: readelf SHF_GNU_RETAIN
+#source: retain1.s
+#target: [supports_gnu_osabi]
+#readelf: -S --wide
+
+#...
+  \[[ 0-9]+\] .bss.retain0.*WAR.*
+  \[[ 0-9]+\] .bss.retain1.*WAR.*
+  \[[ 0-9]+\] .data.retain2.*WAR.*
+  \[[ 0-9]+\] .bss.sretain0.*WAR.*
+  \[[ 0-9]+\] .bss.sretain1.*WAR.*
+  \[[ 0-9]+\] .data.sretain2.*WAR.*
+  \[[ 0-9]+\] .text.fnretain1.*AXR.*
+#...
+  \[[ 0-9]+\] .bss.lsretain0.*WAR.*
+  \[[ 0-9]+\] .bss.lsretain1.*WAR.*
+  \[[ 0-9]+\] .data.lsretain2.*WAR.*
+#pass
diff --git a/binutils/testsuite/binutils-all/retain1b.d b/binutils/testsuite/binutils-all/retain1b.d
new file mode 100644
index 0000000..12bc388
--- /dev/null
+++ b/binutils/testsuite/binutils-all/retain1b.d
@@ -0,0 +1,46 @@
+#name: -t (section details) for readelf SHF_GNU_RETAIN
+#source: retain1.s
+#target: [supports_gnu_osabi]
+#readelf: -S -t --wide
+
+#...
+  \[[ 0-9]+\] .bss.retain0
+#...
+       \[0+200003\]: WRITE, ALLOC, GNU_RETAIN
+#...
+  \[[ 0-9]+\] .bss.retain1
+#...
+       \[0+200003\]: WRITE, ALLOC, GNU_RETAIN
+#...
+  \[[ 0-9]+\] .data.retain2
+#...
+       \[0+200003\]: WRITE, ALLOC, GNU_RETAIN
+#...
+  \[[ 0-9]+\] .bss.sretain0
+#...
+       \[0+200003\]: WRITE, ALLOC, GNU_RETAIN
+#...
+  \[[ 0-9]+\] .bss.sretain1
+#...
+       \[0+200003\]: WRITE, ALLOC, GNU_RETAIN
+#...
+  \[[ 0-9]+\] .data.sretain2
+#...
+       \[0+200003\]: WRITE, ALLOC, GNU_RETAIN
+#...
+  \[[ 0-9]+\] .text.fnretain1
+#...
+       \[0+200006\]: ALLOC, EXEC, GNU_RETAIN
+#...
+  \[[ 0-9]+\] .bss.lsretain0
+#...
+       \[0+200003\]: WRITE, ALLOC, GNU_RETAIN
+#...
+  \[[ 0-9]+\] .bss.lsretain1
+#...
+       \[0+200003\]: WRITE, ALLOC, GNU_RETAIN
+#...
+  \[[ 0-9]+\] .data.lsretain2
+#...
+       \[0+200003\]: WRITE, ALLOC, GNU_RETAIN
+#pass
diff --git a/binutils/testsuite/lib/binutils-common.exp b/binutils/testsuite/lib/binutils-common.exp
index b9a1e6e..a43639b 100644
--- a/binutils/testsuite/lib/binutils-common.exp
+++ b/binutils/testsuite/lib/binutils-common.exp
@@ -195,13 +195,15 @@ proc match_target { target } {
 
 # True if the ELF target supports setting the ELF header OSABI field
 # to ELFOSABI_GNU or ELFOSABI_FREEBSD, a requirement for STT_GNU_IFUNC
-# symbol and SHF_GNU_MBIND section support.
+# symbol and SHF_GNU_MBIND or SHF_GNU_RETAIN section support.
 #
 # This generally depends on the target OS only, however there are a
 # number of exceptions for bare metal targets as follows.  The MSP430
 # and Visium targets set OSABI to ELFOSABI_STANDALONE.  Likewise
 # non-EABI ARM targets set OSABI to ELFOSABI_ARM
 #
+# Non-Linux HPPA defaults to ELFOSABI_HPUX.
+#
 # Note that some TI C6X targets use ELFOSABI_C6000_* but one doesn't,
 # so we don't try to sort out tic6x here.  (The effect is that linker
 # testcases will generally need to exclude tic6x or use a -m option.)
@@ -227,6 +229,7 @@ proc supports_gnu_osabi {} {
     }
     if { [istarget "arm*-*-*"]
 	 || [istarget "msp430-*-*"]
+	 || [istarget "hppa-unknown-elf"]
 	 || [istarget "visium-*-*"] } {
 	return 0
     }