Re: [Gold] problem building linux kernel

[Doug Kwan (éæå) <dougkwan at google dot com>]

This is an uninitialized-variable bug.  Depenidng of whether KEEP_LEFT
or KEEP_RIGHT is set, we will propagate the left or right operand's
alignment.  However, not all sub-classes of Expression return
alignment in Expression::value().  In particular,
Symbol_expression::value() does not and causes this expression to have
garbage alignment value:

init_per_cpu__gdt_page = gdt_page + __per_cpu_load;

Markus: Can you try initializing left_alignment and right_alignment to
zero around line 390 of expression.cc?  That is a band-aid only to
test my theory.

I think the proper fix is to always return a proper alignment (0 if
none is required) in all sub-classes of Expression when a caller of
Expression::value() passes a pointer for alignment result.

-Doug



#define BINARY_EXPRESSION(NAME, OPERATOR, KEEP_LEFT, KEEP_RIGHT, IS_DIV, WARN) \
  class Binary_ ## NAME : public Binary_expression                      \
  {                                                                     \
  public:                                                               \
    Binary_ ## NAME(Expression* left, Expression* right)                \
      : Binary_expression(left, right)                                  \
    { }                                                                 \
                                                                        \
    uint64_t                                                            \
    value(const Expression_eval_info* eei)                              \
    {                                                                   \
      Output_section* left_section;                                     \
      uint64_t left_alignment;                                          \
      uint64_t left = this->left_value(eei, &left_section,              \
                                       &left_alignment);                \
      Output_section* right_section;                                    \
      uint64_t right_alignment;                                         \
      uint64_t right = this->right_value(eei, &right_section,           \
                                         &right_alignment);             \
      if (KEEP_RIGHT && left_section == NULL && right_section != NULL)  \
        {                                                               \
          if (eei->result_section_pointer != NULL)                      \
            *eei->result_section_pointer = right_section;               \
          if (eei->result_alignment_pointer != NULL)                    \
            *eei->result_alignment_pointer = right_alignment;           \
        }                                                               \
      else if (KEEP_LEFT                                                \
               && left_section != NULL                                  \
               && right_section == NULL)                                \
        {                                                               \
          if (eei->result_section_pointer != NULL)                      \
            *eei->result_section_pointer = left_section;                \
          if (eei->result_alignment_pointer != NULL)                    \
            *eei->result_alignment_pointer = right_alignment;           \
        }                                                               \



On Thu, Nov 18, 2010 at 10:26 AM, Doug Kwan (éæå) <dougkwan@google.com> wrote:
> On Thu, Nov 18, 2010 at 7:38 AM, Ian Lance Taylor <iant@google.com> wrote:
>
>> Doug, I don't know what is going on, but there is clearly a 32-x-64
>> problem somewhere. ÂAll these values are sign extended from 32 bits to
>> 64 bits. ÂTry building gold with -m32.
>
> You're spot on. ÂBuilding gold with -m32 does the trick.
>
> Elf file type is EXEC (Executable file)
> Entry point 0x1000000
> There are 6 program headers, starting at offset 64
>
> Program Headers:
> ÂType      Offset  VirtAddr      PhysAddr
> FileSiz ÂMemSiz  Flg Align
> ÂLOAD Â Â Â Â Â 0x001000 0xffffffff81000000 0x0000000001000000
> 0x5bb000 0x5bb000 R E 0x5ffb20100
> ÂLOAD Â Â Â Â Â 0x5bc000 0xffffffff815bb000 0x00000000015bb000
> 0x0645a8 0x0645a8 RWE 0x5ffb20100
> ÂLOAD Â Â Â Â Â 0x621000 0xffffffffff600000 0x0000000001620000
> 0x000888 0x000888 R E 0x5ffb20100
> ÂLOAD Â Â Â Â Â 0x622000 0x0000000000000000 0x0000000001621000
> 0x011f80 0x011f80 RW Â0x5ffb20100
> ÂLOAD Â Â Â Â Â 0x634000 0xffffffff81633000 0x0000000001633000
> 0x0c3000 0x0c3000 RWE 0x5ffb20100
> ÂNOTE Â Â Â Â Â 0x462430 0xffffffff81461430 0x0000000001461430
> 0x000040 0x000040 Â Â 0x4
>
> I will look deeper and see what's wrong.
>
> -Doug
>