PR26580, Size and alignment of commons vs as-needed shared lib

Two pieces to this puzzle:
1) Revert HJ's fix for PR13250 so that size and alignment isn't
   sticky, instead attack the real underlying problem that
   _bfd_generic_link_add_one_symbol does the wrong thing in making a
   common section in a shared library bfd.
2) Save and restore common u.c.p fields, which hold the section and
   alignment.

A better fix for (2) would be to throw away all of that horrible code
saving and restoring the hash table when loading as-needed library
symbols, and instead do a scan over as-needed library symbols before
adding anything.

bfd/
	PR 13250
	PR 26580
	* elflink.c (_bfd_elf_merge_symbol): Make "override" a bfd**.
	Return oldbfd in override when old common should override new
	common.
	(_bfd_elf_add_default_symbol): Adjust to suit.
	(elf_link_add_object_symbols): Likewise.  Pass "override" to
	_bfd_generic_link_add_one_symbol.  Save and restore common u.c.p
	field for --as-needed shared libraries.  Revert pr13250 changes.
ld/
	* testsuite/ld-elf/pr26580-a.s,
	* testsuite/ld-elf/pr26580-b.s,
	* testsuite/ld-elf/pr26580-1.sd,
	* testsuite/ld-elf/pr26580-2.sd: New tests
	* testsuite/ld-elf/comm-data.exp: Run new tests.
	* testsuite/ld-elf/pr26580-a.c,
	* testsuite/ld-elf/pr26580-b.c,
	* testsuite/ld-elf/pr26580-3.out,
	* testsuite/ld-elf/pr26580-4.out: New tests.
	* testsuite/ld-elf/shared.exp: Run new tests.

11 files changed, 113 insertions, 10 deletions

diff --git a/ld/ChangeLog b/ld/ChangeLog
index 0a11b79..4b42f05 100644
--- a/ld/ChangeLog
+++ b/ld/ChangeLog
@@ -1,3 +1,16 @@
+2020-09-08  Alan Modra  <amodra@gmail.com>
+
+	* testsuite/ld-elf/pr26580-a.s,
+	* testsuite/ld-elf/pr26580-b.s,
+	* testsuite/ld-elf/pr26580-1.sd,
+	* testsuite/ld-elf/pr26580-2.sd: New tests
+	* testsuite/ld-elf/comm-data.exp: Run new tests.
+	* testsuite/ld-elf/pr26580-a.c,
+	* testsuite/ld-elf/pr26580-b.c,
+	* testsuite/ld-elf/pr26580-3.out,
+	* testsuite/ld-elf/pr26580-4.out: New tests.
+	* testsuite/ld-elf/shared.exp: Run new tests.
+
 2020-09-04  Alan Modra  <amodra@gmail.com>
 
 	* testsuite/ld-plugin/lto.exp: Don't run pr15146 tests.
diff --git a/ld/testsuite/ld-elf/comm-data.exp b/ld/testsuite/ld-elf/comm-data.exp
index 87ae3b2..16b8e2b 100644
--- a/ld/testsuite/ld-elf/comm-data.exp
+++ b/ld/testsuite/ld-elf/comm-data.exp
@@ -48,6 +48,16 @@ if { [istarget "mips*vr4100*-*-elf*"] \
     append LFLAGS " -call_shared"
 }
 
+# Set the pointer size according to the ELF flavor.
+set AFLAGS ""
+if [is_elf64 "tmpdir/libcomm-data.so"] {
+    append AFLAGS " --defsym ELF64=1"
+}
+# HPUX targets use a different .comm syntax.
+if [istarget "*-*-hpux*"] {
+    append AFLAGS " --defsym HPUX=1"
+}
+
 set testname "Common symbol override test"
 
 # Define a global symbol.
@@ -62,18 +72,16 @@ run_ld_link_tests [list \
 	} \
 	"libcomm-data.so" \
     ] \
+    [list \
+	"libpr26580-1.so" \
+	"$LFLAGS -shared" "" \
+	"$AFLAGS_PIC $AFLAGS" \
+	{ pr26580-b.s } \
+	{ } \
+	"libpr26580-1.so" \
+    ] \
 ]
 
-# Set the pointer size according to the ELF flavor.
-set AFLAGS ""
-if [is_elf64 "tmpdir/libcomm-data.so"] {
-    append AFLAGS " --defsym ELF64=1"
-}
-# HPUX targets use a different .comm syntax.
-if [istarget "*-*-hpux*"] {
-    append AFLAGS " --defsym HPUX=1"
-}
-
 # bfin-elf does not currently support copy relocs.
 setup_xfail "bfin-*-*"
 clear_xfail "bfin-*-linux-uclibc*"
@@ -113,4 +121,20 @@ run_ld_link_tests [list \
 	} \
 	"comm-data3b" \
     ] \
+    [list \
+	"pr26580-1" \
+	"$LFLAGS --as-needed -Ltmpdir -lpr26580-1" "" \
+	"$AFLAGS" \
+	{ pr26580-a.s } \
+	{ {readelf -s pr26580-1.sd} } \
+	"pr26580-1" \
+    ] \
+    [list \
+	"pr26580-2" \
+	"$LFLAGS --no-as-needed -Ltmpdir -lpr26580-1" "" \
+	"$AFLAGS" \
+	{ pr26580-a.s } \
+	{ {readelf -s pr26580-2.sd} } \
+	"pr26580-2" \
+    ] \
 ]
diff --git a/ld/testsuite/ld-elf/pr26580-1.sd b/ld/testsuite/ld-elf/pr26580-1.sd
new file mode 100644
index 0000000..b5adab0
--- /dev/null
+++ b/ld/testsuite/ld-elf/pr26580-1.sd
@@ -0,0 +1,4 @@
+
+#...
+.* 1 OBJECT  GLOBAL DEFAULT .* one
+#pass
diff --git a/ld/testsuite/ld-elf/pr26580-2.sd b/ld/testsuite/ld-elf/pr26580-2.sd
new file mode 100644
index 0000000..265b880
--- /dev/null
+++ b/ld/testsuite/ld-elf/pr26580-2.sd
@@ -0,0 +1,4 @@
+
+#...
+.* 8 OBJECT  GLOBAL DEFAULT .* one
+#pass
diff --git a/ld/testsuite/ld-elf/pr26580-3.out b/ld/testsuite/ld-elf/pr26580-3.out
new file mode 100644
index 0000000..566696f
--- /dev/null
+++ b/ld/testsuite/ld-elf/pr26580-3.out
@@ -0,0 +1,2 @@
+library not loaded
+alignment 1
diff --git a/ld/testsuite/ld-elf/pr26580-4.out b/ld/testsuite/ld-elf/pr26580-4.out
new file mode 100644
index 0000000..d91deea
--- /dev/null
+++ b/ld/testsuite/ld-elf/pr26580-4.out
@@ -0,0 +1,2 @@
+library loaded
+alignment 8
diff --git a/ld/testsuite/ld-elf/pr26580-a.c b/ld/testsuite/ld-elf/pr26580-a.c
new file mode 100644
index 0000000..5557997
--- /dev/null
+++ b/ld/testsuite/ld-elf/pr26580-a.c
@@ -0,0 +1,20 @@
+#include <stdio.h>
+
+extern void __attribute__ ((weak)) foo (void);
+
+char x, y, z;
+
+long
+lowest_align (void *a, void *b, void *c)
+{
+  unsigned long bits = (long) a | (long) b | (long) c;
+  return bits & -bits;
+}
+
+int
+main (void)
+{
+  printf ("library %sloaded\n", &foo ? "" : "not ");
+  printf ("alignment %ld\n", lowest_align (&x, &y, &z));
+  return 0;
+}
diff --git a/ld/testsuite/ld-elf/pr26580-a.s b/ld/testsuite/ld-elf/pr26580-a.s
new file mode 100644
index 0000000..3b70ccc
--- /dev/null
+++ b/ld/testsuite/ld-elf/pr26580-a.s
@@ -0,0 +1,10 @@
+ .text
+ .globl	_start
+ .globl	__start
+_start:
+__start:
+ .ifdef	HPUX
+one	.comm	1
+ .else
+	.comm	one, 1, 1
+ .endif
diff --git a/ld/testsuite/ld-elf/pr26580-b.c b/ld/testsuite/ld-elf/pr26580-b.c
new file mode 100644
index 0000000..e7e13d6
--- /dev/null
+++ b/ld/testsuite/ld-elf/pr26580-b.c
@@ -0,0 +1,3 @@
+long long x, y, z;
+
+void foo (void) {}
diff --git a/ld/testsuite/ld-elf/pr26580-b.s b/ld/testsuite/ld-elf/pr26580-b.s
new file mode 100644
index 0000000..cb06378
--- /dev/null
+++ b/ld/testsuite/ld-elf/pr26580-b.s
@@ -0,0 +1,10 @@
+ .text
+ .globl	_start
+ .globl	__start
+_start:
+__start:
+ .ifdef	HPUX
+one	.comm	8
+ .else
+	.comm	one, 8, 8
+ .endif
diff --git a/ld/testsuite/ld-elf/shared.exp b/ld/testsuite/ld-elf/shared.exp
index 87a40a3..6f53f9c 100644
--- a/ld/testsuite/ld-elf/shared.exp
+++ b/ld/testsuite/ld-elf/shared.exp
@@ -841,6 +841,9 @@ append build_tests {
   {"Dump pr21978.so"
    "-shared" "-fPIC -g -O2"
    {pr21978a.c pr21978b.c} {{objdump {-Sl} pr21978.od}} "pr21978.so"}
+  {"libpr26580-2.so"
+   "-shared" "-fPIC -fcommon"
+   {pr26580-b.c} {} "libpr26580-2.so"}
 }
 
 run_cc_link_tests $build_tests
@@ -1044,6 +1047,14 @@ set run_tests [list \
     [list "Run pr21964-3" \
      "-Wl,--no-as-needed,-rpath,tmpdir tmpdir/pr21964-1a.so tmpdir/pr21964-1b.so tmpdir/pr21964-3a.so" "" \
      {pr21964-3c.c} "pr21964-3" "pass.out" ] \
+    [list "pr26580-3" \
+     "" "" \
+     {pr26580-a.c} "pr26580-3" "pr26580-3.out" "-fcommon" "c" "" \
+     "-Wl,--as-needed tmpdir/libpr26580-2.so" ] \
+    [list "pr26580-4" \
+     "" "" \
+     {pr26580-a.c} "pr26580-4" "pr26580-4.out" "-fcommon" "c" "" \
+     "-Wl,--no-as-needed tmpdir/libpr26580-2.so" ] \
 ]
 
 # NetBSD ELF systems do not currently support the .*_array sections.