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From: "Ozkan Sezer (sezeroz AT gmail DOT com) [via djgpp AT delorie DOT com]" <djgpp AT delorie DOT com>
Date: Fri, 28 Apr 2017 18:24:43 +0300
Message-ID: <CAA2C=vDKwsv7i5jNOGEpOEdokwsWbP3MV_eHU_M6s79cn=NkZg@mail.gmail.com>
Subject: Re: dxe3gen does not handle relocs > 65535
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On 4/28/17, Ozkan Sezer <sezeroz AT gmail DOT com> wrote:
> On 4/28/17, Ozkan Sezer <sezeroz AT gmail DOT com> wrote:
>> dxe3gen does not handle extended relocations, i.e. STYP_NRELOC_OVFL
>> set in hdr->s_flags: it still takes hdr->s_nreloc as number of relocs
>> and ends up generating a broken dxe which leads to bad crashes when
>> loaded.  We have one such c++ project where s_nreloc does overflow.
>>
>> I will be trying a few things with this, but I'd appreciate help or
>> advice or links too:  How should I read the actual number of relocs?
>> Would our current dlopen() still work with this?
>
> Here is a dirty draft (to be tested yet). Comments?
>
> Index: dxe3gen.c
> ===================================================================
> RCS file: /cvs/djgpp/djgpp/src/dxe/dxe3gen.c,v
> retrieving revision 1.23
> diff -u -p -r1.23 dxe3gen.c
> --- dxe3gen.c	4 Oct 2015 10:27:26 -0000	1.23
> +++ dxe3gen.c	28 Apr 2017 08:37:50 -0000
> @@ -937,6 +937,7 @@ static int write_dxe(FILE *inf, FILE *ou
>    char *strings;
>    RELOC *relocs;
>    unsigned int i, j, errcount;
> +  ULONG32 real_nrelocs;
>    size_t hdrsize;
>
>    /* Exported symbols table */
> @@ -953,7 +954,18 @@ static int write_dxe(FILE *inf, FILE *ou
>
>    dh.magic = DXE_MAGIC;
>    dh.element_size = -1;
> -  dh.nrelocs = sc.s_nreloc;
> +  if (sc.s_flags & STYP_NRELOC_OVFL) {
> +    long pos = ftell(inf);
> +    fseek(inf, sc.s_relptr, SEEK_SET);
> +    /* r_vaddr is 1st member of struct external_reloc */
> +    fread(&real_nrelocs, 4, 1, inf);
> +    fseek(inf, pos, SEEK_SET);
> +    dh.nrelocs = --real_nrelocs; /* remove the '+1' */
> +    fprintf(stderr, "%s: real nrelocs: %u\n", progname, real_nrelocs);
> +  }
> +  else {
> +    dh.nrelocs = real_nrelocs = sc.s_nreloc;
> +  }
>    dh.n_exp_syms = 0;
>    dh.exp_table = sizeof(dh);
>    dh.n_deps = opt.num_deps;
> @@ -985,9 +997,12 @@ static int write_dxe(FILE *inf, FILE *ou
>    strings[0] = 0;
>
>    /* Read the relocation table */
> -  relocs = (RELOC *)malloc(sc.s_nreloc * sizeof(RELOC));
> +  relocs = (RELOC *)malloc(real_nrelocs * sizeof(RELOC));
>    fseek(inf, sc.s_relptr, SEEK_SET);
> -  fread(relocs, RELSZ, sc.s_nreloc, inf);
> +  if (sc.s_flags & STYP_NRELOC_OVFL) {
> +    fseek(inf, RELSZ, SEEK_CUR); /* skip the extra one. */
> +  }
> +  fread(relocs, RELSZ, real_nrelocs, inf);
>
>    /* Close input file */
>    fclose(inf);
> @@ -1042,7 +1057,7 @@ static int write_dxe(FILE *inf, FILE *ou
>        int n_abs_relocs = 0, n_rel_relocs = 0;
>
>        /* count the amount of relocations pointing to this symbol */
> -      for (j = 0; j < sc.s_nreloc; j++)
> +      for (j = 0; j < real_nrelocs; j++)
>        {
>          if (relocs[j].r_symndx == i)
>          {
> @@ -1101,7 +1116,7 @@ static int write_dxe(FILE *inf, FILE *ou
>
>        unres_size = newsize;
>
> -      for (j = 0; j < sc.s_nreloc; j++)
> +      for (j = 0; j < real_nrelocs; j++)
>        {
>          if (relocs[j].r_symndx == i)
>          {
> @@ -1202,7 +1217,7 @@ static int write_dxe(FILE *inf, FILE *ou
>
>    /* Compute the amount of valid relocations */
>    DEBUG_PRINT_RELOCATION_DIRECTIVE_PROLOG();
> -  for (i = 0; i < sc.s_nreloc; i++)
> +  for (i = 0; i < real_nrelocs; i++)
>    {
>      DEBUG_PRINT_RELOCATION_DIRECTIVE(i, relocs);
>      if (!VALID_RELOC(relocs[i]))
> @@ -1278,7 +1293,7 @@ static int write_dxe(FILE *inf, FILE *ou
>    free(data);
>
>    /* Output the relocations */
> -  for (i = 0; i < sc.s_nreloc; i++)
> +  for (i = 0; i < real_nrelocs; i++)
>    {
>      if (VALID_RELOC(relocs[i]))
>        fwrite(&relocs[i].r_vaddr, 1, sizeof(relocs[0].r_vaddr), outf);
>

Just tested the above patch by generating out dxe and loading
and running with it: works fine for me.

Any gotchas anyone can notice? Any comments and/or suggestions?
Should apply to CVS?

--
O.S.