[gcc r11-10469] varasm: Fix type confusion bug

[Alex Coplan <acoplan@gcc.gnu.org>]

https://gcc.gnu.org/g:260297e42ca9eddf31aae4acb8a214d3f96a4b16

commit r11-10469-g260297e42ca9eddf31aae4acb8a214d3f96a4b16
Author: Alex Coplan <alex.coplan@arm.com>
Date:   Thu Dec 1 17:36:02 2022 +0000

    varasm: Fix type confusion bug
    
    This patch fixes a type confusion bug in varasm.c:assemble_variable.
    The problem is that the current code calls:
    
      sect = get_variable_section (decl, false);
    
    and then accesses sect->named.name without checking whether the section
    is in fact a named section. In the surrounding else clause, we only know
    that SECTION_STYLE (sect) != SECTION_NOSWITCH, so it is possible that
    the section is an unnamed section.
    
    In practice, this means that we end up doing a wild string compare
    between a function pointer and the string literal ".vtable_map_vars".
    This is because sect->named.name aliases sect->unnamed.callback in the
    section union.
    
    This can be seen in GDB with a simple testcase such as "int x;".
    
    This patch fixes the issue by checking the SECTION_STYLE of the section
    is in fact SECTION_NAMED before trying to do the string comparison.
    
    We drop the existing check of whether sect->named.name is non-NULL
    because this should presumably always be the case for a named section.
    
    gcc/ChangeLog:
    
            * varasm.c (assemble_variable): Fix type confusion bug when
            checking for ".vtable_map_vars" section.
    
    (cherry picked from commit de144fdab17dbbb64ccb540056ab78b4ffb3fbbc)

Diff:
---
 gcc/varasm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/gcc/varasm.c b/gcc/varasm.c
index 93b9c8ef0ee..8e456576010 100644
--- a/gcc/varasm.c
+++ b/gcc/varasm.c
@@ -2380,7 +2380,7 @@ assemble_variable (tree decl, int top_level ATTRIBUTE_UNUSED,
   else
     {
       /* Special-case handling of vtv comdat sections.  */
-      if (sect->named.name
+      if (SECTION_STYLE (sect) == SECTION_NAMED
 	  && (strcmp (sect->named.name, ".vtable_map_vars") == 0))
 	handle_vtv_comdat_section (sect, decl);
       else