[Bug c/12818] New: -fwritable strings triggers bad code generation

[gcc-bugzilla at gcc dot gnu dot org]

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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12818

           Summary: -fwritable strings triggers bad code generation
           Product: gcc
           Version: 3.4
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: fnf at ninemoons dot com
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu


When using -fwritable-strings, the compiler emits two copies of the
strings.  In the supplied example, one of the copies is emitted into a
data area that is supposed to contain pointers to the strings.

In checking some older versions of gcc, it would appear that this
bug first appeared in late May 2003 or early June 2003.

Environment:
System: Linux fred.ninemoons.com 2.4.20-20.9 #1 Mon Aug 18 11:27:43 EDT 2003 i686 athlon i386 GNU/Linux
Architecture: i686

	
host: i686-pc-linux-gnu
build: i686-pc-linux-gnu
target: i686-pc-linux-gnu
configured with: /src/sourceware/gcc/gcc/configure -v --prefix=/usr/local/sourceware --enable-languages=c,c++

How-To-Repeat:

Here is the source code:

	char *names[] = {"alice", "bob", "john"};

	main ()
	{
	  printf ("names[0] = %s\n", names[0]);
	}

This works without -fwritable-strings:

	$ gcc -o j j.c
	$ ./j
	names[0] = alice
	$

It coredumps with -fwritable-strings:

	$ gcc -fwritable-strings -o j j.c
	$ ./j
	Segmentation fault (core dumped)
	$

Here is the generated code:

		 .file   "j.c"
		 .data
	 .LC0:
		 .string "alice"
	 .LC1:
		 .string "bob"
	 .LC2:
		 .string "john"
	 .globl names
		 .align 4
		 .type   names, @object
		 .size   names, 12
	 names:
	 .LC3:
		 .string "alice"
		 .long   .LC3
	 .LC4:
		 .string "bob"
		 .long   .LC4
	 .LC5:
		 .string "john"
		 .long   .LC5
	 .LC6:
		 .string "names[0] = %s\n"
		 .text
	 .globl main
		 .type   main, @function
	 main:
		 pushl   %ebp
		 movl    %esp, %ebp
		 subl    $8, %esp
		 andl    $-16, %esp
		 movl    $0, %eax
		 addl    $15, %eax
		 addl    $15, %eax
		 shrl    $4, %eax
		 sall    $4, %eax
		 subl    %eax, %esp
		 movl    names, %eax
		 movl    %eax, 4(%esp)
		 movl    $.LC6, (%esp)
		 call    printf
		 leave
		 ret
		 .size   main, .-main
		 .section        .note.GNU-stack,"",@progbits
		 .ident  "GCC: (GNU) 3.4 20031028 (experimental)"

 >Fix:
	Workaround is to not use -fwritable-strings