[PATCH] Fix loading of lto_section on strict alignment targets (PR lto/91078).

[Martin Liška]

Hi.

The patch fixes wrong assignment from a char * to lto_section_header
that is seen on strict alignment targets.

I verified it fixes the problem with -fsanitize=undefined:

gcc main.o -flto
../../gcc/lto/lto-common.c:2202:36: runtime error: reference binding to 
misaligned address 0x7f64dac090a7 for type 'const struct lto_section', which 
requires 4 byte alignment
0x7f64dac090a7: note: pointer points here
 00 1b c0 02 09  00 00 00 03 00 00 00 28  b5 2f fd 60 77 00 d5 08  00 e6 d1 3d 
37 20 01 09  00 bf 53
             ^ 
../../gcc/lto/lto-common.c:2202:33: runtime error: load of misaligned address 
0x7f64dac090a7 for type 'const struct lto_section', which requires 4 byte 
alignment
0x7f64dac090a7: note: pointer points here
 00 1b c0 02 09  00 00 00 03 00 00 00 28  b5 2f fd 60 77 00 d5 08  00 e6 d1 3d 
37 20 01 09  00 bf 53
             ^ 

Ready for trunk?
Thanks,
Martin

gcc/lto/ChangeLog:

2019-07-04  Martin Liska  <mli...@suse.cz>

        PR lto/91078
        * lto-common.c (lto_file_finalize): Use memcpy to set
        file_data->lto_section_header.
---
 gcc/lto/lto-common.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)



diff --git a/gcc/lto/lto-common.c b/gcc/lto/lto-common.c
index bc8c2b40387..3c6d7b25ddb 100644
--- a/gcc/lto/lto-common.c
+++ b/gcc/lto/lto-common.c
@@ -2199,7 +2199,7 @@ lto_file_finalize (struct lto_file_decl_data *file_data, lto_file *file)
       return;
     }
 
-  file_data->lto_section_header = *(const lto_section *)data;
+  memcpy (&file_data->lto_section_header, data, sizeof (lto_section));
   lto_check_version (file_data->lto_section_header.major_version,
 		     file_data->lto_section_header.minor_version,
 		     file_data->file_name);