Tortall yasm → 1.2.0

Originally posted on Trac by bird-yasm@anduin.net
Original Trac Ticket

  Description

When yasm_bc_tobytes does more than one iteration in for loop (i in {0...bc->mult_int}) there is no way the offset parameter of output_value calls can be right. This affects fixup generation of elf and possible other targets.

I've hacked up a very unrealistic example of how to reproduce the issue (I've got another one for OMF but that depends on unfinished code):

tst-value-offset-elf64.asm:

section .data
foobar:
        dq      42
section .text
foo:
        times 4 mov rax, [foobar wrt rip]

Assemble the file as elf64.
Use objdump to disassemble and dump relocations:

tst-value-offset-elf64.o:     file format elf64-little

SYMBOL TABLE:
0000000000000000 l    df *ABS*  0000000000000000 tst-value-offset-elf64.asm
0000000000000000 l       .text  0000000000000000 
0000000000000000 l       .data  0000000000000000 
0000000000000000 l    d  .data  0000000000000000 .data
0000000000000000 l    d  .text  0000000000000000 .text

Disassembly of section .text:

0000000000000000 :
   0:   48 8b 05 00 00 00 00    mov    0x0(%rip),%rax        # 0x7
            3: UNKNOWN  .data+0xfffffffffffffffc
            3: UNKNOWN  .data+0xfffffffffffffff5
            3: UNKNOWN  .data+0xffffffffffffffee
            3: UNKNOWN  .data+0xffffffffffffffe7
   7:   48 8b 05 00 00 00 00    mov    0x0(%rip),%rax        # 0xe
   e:   48 8b 05 00 00 00 00    mov    0x0(%rip),%rax        # 0x15
  15:   48 8b 05 00 00 00 00    mov    0x0(%rip),%rax        # 0x1c

One would expect each of the 4 mov instructions to get fixed up, instead there are 4 fixups for the first instruction.

I think the fix would be to make the tobytes bytecode callback take an extra parameter that is either buf/mybuf or the current offset into the buffer.

Trac Attachments

http://www.tortall.net/projects/yasm/attachment/ticket/229/yasm-out...
http://www.tortall.net/projects/yasm/raw-attachment/ticket/229/yasm...
http://www.tortall.net/projects/yasm/timeline?from=2010-11-01T12%3A...

Trac Comments

Changed 8 months ago by bird-yasm@anduin.net

fix proposal that passes the pointer to the beginning of the buffer around.

                  Changed 8 months ago by bird-yasm@anduin.net

      attachment
        yasm-output_value_offset-1b.diff​
          added

fix proposal that passes the pointer to the beginning of the buffer around.

      attachment
        yasm-output_value_offset-1b.diff​
          added