[binutils-gdb] gas: copy st_size only if unset

[Fangrui Song]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=867b8c308a40e79f90db4051cafc273f00f881fb

commit 867b8c308a40e79f90db4051cafc273f00f881fb
Author: Fangrui Song <i@maskray.me>
Date:   Mon Apr 4 08:43:50 2022 -0700

    gas: copy st_size only if unset
    
    For
    ```
    .size foo1, 1
    foo1:
    
    .set bar1, foo1
    .size bar1, 2
    .size bar2, 2
    .set bar2, foo1
    
    .set bar3, foo2
    .size bar3, 2
    .size bar4, 2
    .set bar4, foo2
    
    .size foo2, 1
    foo2:
    ```
    
    bar1's size is 2 while bar2, bar3, bar4's is 1. The behavior of bar1 makes sense
    (generally directives on the new symbol should win) and is relied upon by glibc
    stdio-common/errlist.c:
    
    ```
            .hidden _sys_errlist_internal
            .globl  _sys_errlist_internal
            .type   _sys_errlist_internal, @object
            .size   _sys_errlist_internal, 1072
    _sys_errlist_internal:
    
            .globl __GLIBC_2_1_sys_errlist
            .set __GLIBC_2_1_sys_errlist, _sys_errlist_internal
            .type __GLIBC_2_1_sys_errlist, %object
            .size __GLIBC_2_1_sys_errlist, 125 * (64 / 8)
    
    // glibc expects that .size __GLIBC_2_1_sys_errlist, 125 * (64 / 8) wins.
    ```
    
    The behavior of bar2/bar3/bar4 seems brittle. To avoid the reordering of the two
    code blocks which will result in the bar3 situation, glibc compiles errlist.c
    with gcc -fno-toplevel-reorder (previously -fno-unit-at-a-time).
    
    To fix the inconsistency and improve robustness, make bar2/bar3/bar4 match bar1,
    removing the directive order sensitivity.
    
    There is a pity that `.size dest, 0` is indistinguishable from the case where
    dest is unset, but the compromise seems fine.
    
        PR gas/29012
        * config/obj-elf.c (elf_copy_symbol_attributes): don't copy if src's size
          has been set.
        * testsuite/gas/elf/elf.exp: New test.
        * testsuite/gas/elf/size.d: New file.
        * testsuite/gas/elf/size.s: Likewise.

Diff:
---
 gas/config/obj-elf.c          | 24 ++++++++++--------------
 gas/testsuite/gas/elf/elf.exp |  1 +
 gas/testsuite/gas/elf/size.d  | 14 ++++++++++++++
 gas/testsuite/gas/elf/size.s  | 23 +++++++++++++++++++++++
 4 files changed, 48 insertions(+), 14 deletions(-)

diff --git a/gas/config/obj-elf.c b/gas/config/obj-elf.c
index b56f8aa5220..b218ff6a574 100644
--- a/gas/config/obj-elf.c
+++ b/gas/config/obj-elf.c
@@ -2154,27 +2154,23 @@ elf_obj_symbol_clone_hook (symbolS *newsym, symbolS *orgsym ATTRIBUTE_UNUSED)
     }
 }
 
-/* When setting one symbol equal to another, by default we probably
-   want them to have the same "size", whatever it means in the current
-   context.  */
-
 void
 elf_copy_symbol_attributes (symbolS *dest, symbolS *src)
 {
   struct elf_obj_sy *srcelf = symbol_get_obj (src);
   struct elf_obj_sy *destelf = symbol_get_obj (dest);
-  if (srcelf->size)
-    {
-      if (destelf->size == NULL)
-	destelf->size = XNEW (expressionS);
-      *destelf->size = *srcelf->size;
-    }
-  else
+  /* If size is unset, copy size from src.  Because we don't track whether
+     .size has been used, we can't differentiate .size dest, 0 from the case
+     where dest's size is unset.  */
+  if (!destelf->size && S_GET_SIZE (dest) == 0)
     {
-      free (destelf->size);
-      destelf->size = NULL;
+      if (srcelf->size)
+	{
+	  destelf->size = XNEW (expressionS);
+	  *destelf->size = *srcelf->size;
+	}
+      S_SET_SIZE (dest, S_GET_SIZE (src));
     }
-  S_SET_SIZE (dest, S_GET_SIZE (src));
   /* Don't copy visibility.  */
   S_SET_OTHER (dest, (ELF_ST_VISIBILITY (S_GET_OTHER (dest))
 		      | (S_GET_OTHER (src) & ~ELF_ST_VISIBILITY (-1))));
diff --git a/gas/testsuite/gas/elf/elf.exp b/gas/testsuite/gas/elf/elf.exp
index 081ab4ec683..963730a87a5 100644
--- a/gas/testsuite/gas/elf/elf.exp
+++ b/gas/testsuite/gas/elf/elf.exp
@@ -277,6 +277,7 @@ if { [is_elf_format] } then {
     run_dump_test "section28"
     run_dump_test "section29"
     run_dump_test "sh-link-zero"
+    run_dump_test "size"
     run_dump_test "dwarf2-1" $dump_opts
     run_dump_test "dwarf2-2" $dump_opts
     run_dump_test "dwarf2-3" $dump_opts
diff --git a/gas/testsuite/gas/elf/size.d b/gas/testsuite/gas/elf/size.d
new file mode 100644
index 00000000000..51bf4eb66ca
--- /dev/null
+++ b/gas/testsuite/gas/elf/size.d
@@ -0,0 +1,14 @@
+#readelf: -sW
+#name: ELF symbol size
+
+#...
+ +[0-9]+: 0+ +1 +NOTYPE +LOCAL +DEFAULT +[0-9]+ +foo1
+ +[0-9]+: 0+ +2 +NOTYPE +LOCAL +DEFAULT +[0-9]+ +bar1
+ +[0-9]+: 0+ +2 +NOTYPE +LOCAL +DEFAULT +[0-9]+ +bar2
+ +[0-9]+: 0+ +2 +NOTYPE +LOCAL +DEFAULT +[0-9]+ +bar3
+ +[0-9]+: 0+ +3 +NOTYPE +LOCAL +DEFAULT +[0-9]+ +foo2
+ +[0-9]+: 0+ +2 +NOTYPE +LOCAL +DEFAULT +[0-9]+ +bar4
+ +[0-9]+: 0+ +1 +NOTYPE +LOCAL +DEFAULT +[0-9]+ +bar5
+ +[0-9]+: 0+ +3 +NOTYPE +LOCAL +DEFAULT +[0-9]+ +bar6
+ +[0-9]+: 0+ +3 +NOTYPE +LOCAL +DEFAULT +[0-9]+ +bar7
+#pass
diff --git a/gas/testsuite/gas/elf/size.s b/gas/testsuite/gas/elf/size.s
new file mode 100644
index 00000000000..92865565d7a
--- /dev/null
+++ b/gas/testsuite/gas/elf/size.s
@@ -0,0 +1,23 @@
+.text
+
+.size foo1, 1
+foo1:
+
+.set bar1, foo1
+.size bar1, 2
+.size bar2, 2
+.set bar2, foo1
+
+.set bar3, foo2
+.size bar3, 2
+.size bar4, 2
+.set bar4, foo2
+
+.set bar5, foo1
+.set bar6, foo2
+
+.size foo2, 3
+foo2:
+
+.set bar7, foo1
+.set bar7, foo2