bfd/PE: respect SEC_ALLOC when deciding whether to force IMAGE_SCN_MEM_DISCARDABLE

While in the common case sections like .reloc don't need to be accessed
by a binary (that's the job of the loader), there are rare cases where
the situation is different. Unconditionally forcing the discardable flag
is therefore unhelpful. Avoid doing so when SEC_ALLOC is set, which
would in particular be the case when .reloc isn't (solely) linker-
generated.

While adjusting the comment, drop the wrong (stale?) following sentence:
.rsrc, as per its table entry, doesn't need to be writable. And
commenting on it wanting to be readable would then need to be repeated
for all other sections as well.

bfd/peXXigen.c

@@ -920,7 +920,7 @@ _bfd_XX_only_swap_filehdr_out (bfd * abfd, void * in, void * out)
 
 unsigned int
 _bfd_XXi_swap_scnhdr_out (bfd * abfd, void * in, void * out,
-			  const asection *section ATTRIBUTE_UNUSED)
+			  const asection *section)
 {
   struct internal_scnhdr *scnhdr_int = (struct internal_scnhdr *) in;
   SCNHDR *scnhdr_ext = (SCNHDR *) out;
@@ -989,9 +989,8 @@ _bfd_XXi_swap_scnhdr_out (bfd * abfd, void * in, void * out,
        sections (.idata, .data, .bss, .CRT) must have IMAGE_SCN_MEM_WRITE set
        (this is especially important when dealing with the .idata section since
        the addresses for routines from .dlls must be overwritten).  If .reloc
-       section data is ever generated, we must add IMAGE_SCN_MEM_DISCARDABLE
+       section data is ever generated, we generally need to add
-       (0x02000000).  Also, the resource data should also be read and
+       IMAGE_SCN_MEM_DISCARDABLE (0x02000000).  */
-       writable.  */
 
     /* FIXME: Alignment is also encoded in this field, at least on
        ARM-WINCE.  Although - how do we get the original alignment field
@@ -1037,10 +1036,16 @@ _bfd_XXi_swap_scnhdr_out (bfd * abfd, void * in, void * out,
 	 p++)
       if (memcmp (scnhdr_int->s_name, p->section_name, SCNNMLEN) == 0)
 	{
+	  unsigned long must_have = p->must_have;
+
 	  if (memcmp (scnhdr_int->s_name, ".text", sizeof ".text")
 	      || (bfd_get_file_flags (abfd) & WP_TEXT))
 	    scnhdr_int->s_flags &= ~IMAGE_SCN_MEM_WRITE;
-	  scnhdr_int->s_flags |= p->must_have;
+	  /* Avoid forcing in the discardable flag if the section itself is
+	     allocated.  */
+	  if (section->flags & SEC_ALLOC)
+	    must_have &= ~IMAGE_SCN_MEM_DISCARDABLE;
+	  scnhdr_int->s_flags |= must_have;
 	  break;
 	}
 

gas/testsuite/gas/pe/pe.exp

@@ -38,6 +38,8 @@ run_dump_test "section-exclude"
 
 run_dump_test "set"
 
+run_dump_test "reloc"
+
 if { [istarget "aarch64-*-*"] || [istarget "arm*-*-*"] || [istarget "i*86-*-*"]
     || [istarget "x86_64-*-*"] } then {
   run_dump_test "cv_comp"

gas/testsuite/gas/pe/reloc.d

@@ -0,0 +1,13 @@
+#as: --no-pad-sections
+#objdump: -wPsections
+#name: .reloc section attributes
+
+.*: .*
+
+Section headers.*:
+ # Name    *paddr *vaddr *size  .* Flags
+ 1 \.text  *0*0000 0*0000 0*0(4|10) .* Align: (4|16) EXECUTE,READ,CODE
+ 2 \.data  *0*0000 0*0000 0*0(8|10) .* Align: (4|16) READ,WRITE,INITIALIZED DATA
+ 3 \.bss   .*
+ 4 \.rdata *0*0000 0*0000 0*0(8|10) .* Align: (4|16) READ,INITIALIZED DATA
+ 5 \.reloc *0*0000 0*0000 0*00c .* Align: 4 READ,INITIALIZED DATA

gas/testsuite/gas/pe/reloc.s

@@ -0,0 +1,19 @@
+	.text
+	.global _start
+_start:
+	.nop
+
+	.section .rdata, "r"
+	.dc.a	_start
+	.dc.a	.
+
+	.data
+.L1:	.rva	_start
+.L2:	.rva	.
+
+	.section .reloc, "r"
+	.p2align 2
+	.rva	.data
+	.long	2 * 4 + 2 * 2
+	.short	.L1 - .data + (3 << 12)
+	.short	.L2 - .data + (3 << 12)

ld/testsuite/ld-pe/pe.exp

@@ -137,6 +137,9 @@ run_dump_test "orphan"
 run_dump_test "orphan_nu"
 
 run_dump_test "reloc"
+run_dump_test "reloc2a"
+run_dump_test "reloc2b"
+run_dump_test "reloc2c"
 
 run_dump_test "weakdef-1"
 

ld/testsuite/ld-pe/reloc2.s

@@ -0,0 +1,19 @@
+	.text
+	.global _start
+_start:
+	.nop
+
+	.section .rdata, "r"
+	.dc.a	_start
+	.dc.a	.
+
+	.data
+.L1:	.rva	_start
+.L2:	.rva	.
+
+	.section .reloc, "r"
+	.p2align 2
+	.rva	.data
+	.long	2 * 4 + 2 * 2
+	.short	.L1 - .data + (3 << 12)
+	.short	.L2 - .data + (3 << 12)

ld/testsuite/ld-pe/reloc2a.d

@@ -0,0 +1,35 @@
+#source: reloc2.s
+#as: --no-pad-sections
+#name: PE .reloc section attributes (builtin+custom)
+#ld: --enable-reloc-section --section-align=0x1000 -e _start
+#objdump: -hpwPsections
+
+.*:     file format .*
+
+#...
+PE File Base Relocations.*
+Virtual Address: .* Number of fixups 2
+[ 	]*reloc    0 offset    0 .* HIGHLOW
+[ 	]*reloc    1 offset    [48] .* HIGHLOW
+
+Virtual Address: .* Number of fixups 2
+[ 	]*reloc    0 offset    0 .* (HIGHLOW|DIR64)
+[ 	]*reloc    1 offset    [48] .* (HIGHLOW|DIR64)
+
+#?private flags = .*
+
+Section headers.*:
+ # Name    *paddr *vaddr *size  .* Flags
+ 1 \.text  *0000.* 0.*000 0*200 .* EXECUTE,READ,CODE
+ 2 \.data  *0000.* 0.*000 0*200 .* READ,WRITE,INITIALIZED DATA
+ 3 \.rdata *0000.* 0.*000 0*200 .* READ,INITIALIZED DATA
+ 4 \.idata *0000.* 0.*000 0*200 .* READ,INITIALIZED DATA
+ 5 \.reloc *0000.* 0.*000 0*200 .* READ,INITIALIZED DATA
+
+Sections:
+Idx Name    *Size     *VMA    *LMA  *File off  .* Flags
+  0 \.text  *0*(1?4|8|10) .*000  .*000  0*0000... .* CONTENTS, ALLOC, LOAD, READONLY, CODE
+  1 \.data  *0*(8|10) .*000  .*000  0*0000... .* CONTENTS, ALLOC, LOAD, DATA
+  2 \.rdata *0*0000.. .*000  .*000  0*0000... .* CONTENTS, ALLOC, LOAD, READONLY, DATA
+  3 \.idata *0*1(4|8) .*000  .*000  0*0000... .* CONTENTS, ALLOC, LOAD, READONLY, DATA
+  4 \.reloc *0*000018 .*000  .*000  0*0000... .* CONTENTS, ALLOC, LOAD, READONLY, DATA

ld/testsuite/ld-pe/reloc2b.d

@@ -0,0 +1,32 @@
+#source: reloc2.s RUN_OBJCOPY
+#as: --no-pad-sections
+#name: PE .reloc section attributes (builtin only)
+#objcopy_objects: --rename-section .reloc=.rdata$1
+#ld: --enable-reloc-section --section-align=0x1000 -e _start
+#objdump: -hpwPsections
+
+.*:     file format .*
+
+#...
+PE File Base Relocations.*
+Virtual Address: .* Number of fixups 2
+[ 	]*reloc    0 offset    0 .* (HIGHLOW|DIR64)
+[ 	]*reloc    1 offset    [48] .* (HIGHLOW|DIR64)
+
+#?private flags = .*
+
+Section headers.*:
+ # Name    *paddr *vaddr *size  .* Flags
+ 1 \.text  *0000.* 0.*000 0*200 .* EXECUTE,READ,CODE
+ 2 \.data  *0000.* 0.*000 0*200 .* READ,WRITE,INITIALIZED DATA
+ 3 \.rdata *0000.* 0.*000 0*200 .* READ,INITIALIZED DATA
+ 4 \.idata *0000.* 0.*000 0*200 .* READ,INITIALIZED DATA
+ 5 \.reloc *0000.* 0.*000 0*200 .* DISCARDABLE,READ,INITIALIZED DATA
+
+Sections:
+Idx Name    *Size     *VMA    *LMA  *File off  .* Flags
+  0 \.text  *0*(1?4|8|10) .*000  .*000  0*0000... .* CONTENTS, ALLOC, LOAD, READONLY, CODE
+  1 \.data  *0*(8|10) .*000  .*000  0*0000... .* CONTENTS, ALLOC, LOAD, DATA
+  2 \.rdata *0*0000.. .*000  .*000  0*0000... .* CONTENTS, ALLOC, LOAD, READONLY, DATA
+  3 \.idata *0*1(4|8) .*000  .*000  0*0000... .* CONTENTS, ALLOC, LOAD, READONLY, DATA
+  4 \.reloc *0*00000c .*000  .*000  0*0000... .* CONTENTS, LOAD, READONLY, DATA

ld/testsuite/ld-pe/reloc2c.d

@@ -0,0 +1,31 @@
+#source: reloc2.s
+#as: --no-pad-sections
+#name: PE .reloc section attributes (custom only)
+#ld: --disable-reloc-section --section-align=0x1000 -e _start
+#objdump: -hpwPsections
+
+.*:     file format .*
+
+#...
+PE File Base Relocations.*
+Virtual Address: .* Number of fixups 2
+[ 	]*reloc    0 offset    0 .* HIGHLOW
+[ 	]*reloc    1 offset    [48] .* HIGHLOW
+
+#?private flags = .*
+
+Section headers.*:
+ # Name    *paddr *vaddr *size  .* Flags
+ 1 \.text  *0000.* 0.*000 0*200 .* EXECUTE,READ,CODE
+ 2 \.data  *0000.* 0.*000 0*200 .* READ,WRITE,INITIALIZED DATA
+ 3 \.rdata *0000.* 0.*000 0*200 .* READ,INITIALIZED DATA
+ 4 \.idata *0000.* 0.*000 0*200 .* READ,INITIALIZED DATA
+ 5 \.reloc *0000.* 0.*000 0*200 .* READ,INITIALIZED DATA
+
+Sections:
+Idx Name    *Size     *VMA    *LMA  *File off  .* Flags
+  0 \.text  *0*(1?4|8|10) .*000  .*000  0*0000... .* CONTENTS, ALLOC, LOAD, READONLY, CODE
+  1 \.data  *0*(8|10) .*000  .*000  0*0000... .* CONTENTS, ALLOC, LOAD, DATA
+  2 \.rdata *0*0000.. .*000  .*000  0*0000... .* CONTENTS, ALLOC, LOAD, READONLY, DATA
+  3 \.idata *0*1(4|8) .*000  .*000  0*0000... .* CONTENTS, ALLOC, LOAD, READONLY, DATA
+  4 \.reloc *0*00000c .*000  .*000  0*0000... .* CONTENTS, ALLOC, LOAD, READONLY, DATA