[PATCH] Orphan sections and NOLOAD output section

[Eric Botcazou <botcazou@adacore.com>]

[-- Attachment #1: Type: text/plain, Size: 1216 bytes --]

Hi,

we recently got a report about a counter-intuitive behavior of the GNU linker
for orphan sections matched by a NOLOAD output section, which turned out to be
an exact duplicate of:
  https://stackoverflow.com/questions/48764136/gcc-noload-directive-cause-wrong-memory-mapping

What happens is that the effect of the command:

  .foo (NOLOAD) : {}

is not equivalent to that of:

  .foo (NOLOAD) : { *(.foo) }

when there is more than 1 object file containing a .foo section: the former
will output two .foo sections, the first with PROGBITS and the second with
NOBITS, where the latter will output only one with NOBITS.

I think that the commands are essentially equivalent so the linker ought to yield
the same outcome, namely the single output section with NOBITS.

Tested on x86-64/Linux, OK for the mainline?


2022-04-21  Eric Botcazou  <ebotcazou@adacore.com>

ld/
	* ldelf.c (ldelf_place_orphan): Match only by name for a NOLOAD
	output section present in the script.
	* testsuite/ld-elf/orphan-13.d: New file.
	* testsuite/ld-elf/orphan-13.ld: Likewise.
	* testsuite/ld-elf/orphan-13a.s: Likewise.
	* testsuite/ld-elf/orphan-13b.s: Likewise.
	* testsuite/ld-elf/orphan-13c.s: Likewise.

-- 
Eric Botcazou

[-- Attachment #2: p.diff --]
[-- Type: text/x-patch, Size: 2787 bytes --]

diff --git a/ld/ldelf.c b/ld/ldelf.c
index 4094640b3f7..35718a9113b 100644
--- a/ld/ldelf.c
+++ b/ld/ldelf.c
@@ -2098,13 +2098,17 @@ ldelf_place_orphan (asection *s, const char *secname, int constraint)
 	   lang_insert_orphan to create a new output section.  */
 	constraint = SPECIAL;
 
-	/* Check to see if we already have an output section statement
-	   with this name, and its bfd section has compatible flags.
+	/* Check to see if we already have an output section statement with
+	   this name, and it was either present in the script with a special
+	   type (knowing that lang_insert_orphan only creates normal_section
+	   output sections) or its BFD section has compatible flags.
+
 	   If the section already exists but does not have any flags
 	   set, then it has been created by the linker, possibly as a
 	   result of a --section-start command line switch.  */
 	if (os->bfd_section != NULL
-	    && (os->bfd_section->flags == 0
+	    && (os->sectype == noload_section
+		|| os->bfd_section->flags == 0
 		|| (((s->flags ^ os->bfd_section->flags)
 		     & (SEC_LOAD | SEC_ALLOC)) == 0
 		    && (!elfinput
diff --git a/ld/testsuite/ld-elf/orphan-13.d b/ld/testsuite/ld-elf/orphan-13.d
new file mode 100644
index 00000000000..8f867dc8938
--- /dev/null
+++ b/ld/testsuite/ld-elf/orphan-13.d
@@ -0,0 +1,12 @@
+#source: orphan-13a.s
+#source: orphan-13b.s
+#source: orphan-13c.s
+#ld: -T orphan-13.ld
+#readelf: -S --wide
+#xfail: [uses_genelf]
+#xfail: xstormy16-*-*
+
+#...
+  \[[ 0-9]+\] \.foo +NOBITS +[0-9a-f]+ +[0-9a-f]+ +0+30 +0+ +A +0 +0 +[0-9]+
+  \[[ 0-9]+\] [._][^f].*
+#pass
diff --git a/ld/testsuite/ld-elf/orphan-13.ld b/ld/testsuite/ld-elf/orphan-13.ld
new file mode 100644
index 00000000000..face613f8bd
--- /dev/null
+++ b/ld/testsuite/ld-elf/orphan-13.ld
@@ -0,0 +1,7 @@
+SECTIONS
+{
+  . = SIZEOF_HEADERS;
+  .text : { *(.text) }
+  .data : { *(.data) }
+  .foo (NOLOAD) : {}
+}
diff --git a/ld/testsuite/ld-elf/orphan-13a.s b/ld/testsuite/ld-elf/orphan-13a.s
new file mode 100644
index 00000000000..a8a6f364455
--- /dev/null
+++ b/ld/testsuite/ld-elf/orphan-13a.s
@@ -0,0 +1,14 @@
+ .globl main
+ .globl _main
+ .globl start
+ .globl _start
+ .globl __start
+ .text
+main:
+_main:
+start:
+_start:
+__start:
+
+ .section .foo,"a",%progbits
+ .long 1,1,1,1
diff --git a/ld/testsuite/ld-elf/orphan-13b.s b/ld/testsuite/ld-elf/orphan-13b.s
new file mode 100644
index 00000000000..c475eb11d1b
--- /dev/null
+++ b/ld/testsuite/ld-elf/orphan-13b.s
@@ -0,0 +1,2 @@
+ .section .foo,"a",%progbits
+ .long 1,1,1,1
diff --git a/ld/testsuite/ld-elf/orphan-13c.s b/ld/testsuite/ld-elf/orphan-13c.s
new file mode 100644
index 00000000000..c475eb11d1b
--- /dev/null
+++ b/ld/testsuite/ld-elf/orphan-13c.s
@@ -0,0 +1,2 @@
+ .section .foo,"a",%progbits
+ .long 1,1,1,1