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Support for Win32 safeseh (BR 195417)

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This is basically not a bug report, but a feature request.

It's desired to be able to link .obj modules compiled with 'nasm -f
win32' with Microsoft 'link /safeseh'. As well as to register symbols
(commonly subroutine's entry points or even external symbols) as "safe
handlers." In order to achieve this, several points are required.

First of all, object module has to have absolute symbol named @feat.00
with value of 1. This can actually be achived by adding 'absolute 1'
and '@feat.00:' to source code, but it's desirable that it's
autogenerated for win32 modules.

Handler registration is essentially symbol's *index* in current
module's symbol table in .sxdata, segment with 0x200 segment flags, an
"info" segment. It's also essential that symbol has type 0x20 (see
below). All this is depicted in following framgents of 'objdump -xD'
output:

Sections:
Idx Name          Size      VMA       LMA       File off  Algn
  0 .sxdata       00000004  00000000  00000000  0000003c  2**2
                  CONTENTS, READONLY, DEBUGGING

SYMBOL TABLE:
...
[  5](sec -1)(fl 0x00)(ty   0)(scl   3) (nx 0) 0x00000001 @feat.00
[  6](sec  0)(fl 0x00)(ty  20)(scl   2) (nx 0) 0x00000000 _handler
...
<.sxdata>
0: 06 00 00 00

Note [6] and (ty 20) in _handle line in SYMBOL TABLE. "06 00 00 00" in
.sxdata is little-endian 6, _handler's index. This is what makes up
"registration." It's impossible to achieve this with current nasm
facilities and it's probably appropriate to introduce a directive for
it, 'safeseh _handler' is probably most natural choice.
This commit is contained in:
Andy Polyakov 2008-05-23 18:37:52 -07:00 committed by H. Peter Anvin
parent e6a5cb536a
commit 4401cc79a2
1 changed files with 75 additions and 7 deletions
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82
output/outcoff.c
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@ -88,6 +88,8 @@ struct Symbol {
int section; /* section number where it's defined
* - in COFF codes, not NASM codes */
bool is_global; /* is it a global symbol or not? */
int16_t type; /* 0 - notype, 0x20 - function */
int32_t namlen; /* full name length */
};
static FILE *coffp;
@ -382,6 +384,7 @@ static void coff_deflabel(char *name, int32_t segment, int64_t offset,
sym = saa_wstruct(syms);
sym->strpos = pos;
sym->namlen = strlen(name);
if (pos == -1)
strcpy(sym->name, name);
sym->is_global = !!is_global;
@ -689,6 +692,53 @@ static int coff_directives(char *directive, char *value, int pass)
}
AddExport(name);
return 1;
} else if (win32 && !strcmp(directive,"safeseh")) {
static int sxseg=-1;
int i;
if (sxseg==-1)
{ for (i = 0; i < nsects; i++)
if (!strcmp(".sxdata",sects[i]->name))
break;
if (i == nsects)
sxseg = coff_make_section(".sxdata",0x200);
else
sxseg = i;
}
if (pass==2) {
uint32_t n;
saa_rewind(syms);
for (n = 0; n < nsyms; n++) {
struct Symbol *sym = saa_rstruct(syms);
bool equals;
/* sym->strpos is biased by 4, because symbol
* table is prefixed with table length */
if (sym->strpos >=4) {
char *name = nasm_malloc(sym->namlen+1);
saa_fread(strs,sym->strpos-4,name,sym->namlen);
name[sym->namlen]='\0';
equals = !strcmp(value,name);
nasm_free(name);
}
else
equals = !strcmp(value,sym->name);
if (equals) {
/* this value arithmetics effectively reflects
* initsym in coff_write(): 2 for file, 1 for
* .absolute and two per each section */
unsigned char value[4],*p=value;
WRITELONG(p,n + 2 + 1 + nsects*2);
coff_sect_write(sects[sxseg],value,4);
sym->type = 0x20;
break;
}
}
if (n == nsyms) {
error(ERR_FATAL,"`safeseh' directive requires valid symbol");
}
}
return 1;
}
return 0;
}
@ -699,6 +749,21 @@ static void coff_write(void)
int i;
BuildExportTable(); /* fill in the .drectve section with -export's */
if (win32) {
/* add default value for @feat.00, this allows to 'link /safeseh' */
uint32_t n;
saa_rewind(syms);
for (n = 0; n < nsyms; n++) {
struct Symbol *sym = saa_rstruct(syms);
if (sym->strpos == -1 && !strcmp("@feat.00",sym->name))
break;
}
if (n == nsyms)
coff_deflabel("@feat.00",NO_SEG,1,0,NULL);
}
/*
* Work out how big the file will get. Calculate the start of
* the `real' symbols at the same time.
@ -806,7 +871,7 @@ static void coff_write_relocs(struct Section *s)
}
static void coff_symbol(char *name, int32_t strpos, int32_t value,
int section, int type, int aux)
int section, int type, int storageclass, int aux)
{
char padname[8];
@ -820,8 +885,8 @@ static void coff_symbol(char *name, int32_t strpos, int32_t value,
}
fwriteint32_t(value, coffp);
fwriteint16_t(section, coffp);
fwriteint16_t(0, coffp);
fputc(type, coffp);
fwriteint16_t(type, coffp);
fputc(storageclass, coffp);
fputc(aux, coffp);
}
@ -833,7 +898,7 @@ static void coff_write_symbols(void)
/*
* The `.file' record, and the file name auxiliary record.
*/
coff_symbol(".file", 0L, 0L, -2, 0x67, 1);
coff_symbol(".file", 0L, 0L, -2, 0, 0x67, 1);
memset(filename, 0, 18);
strncpy(filename, coff_infile, 18);
fwrite(filename, 18, 1, coffp);
@ -844,7 +909,7 @@ static void coff_write_symbols(void)
memset(filename, 0, 18); /* useful zeroed buffer */
for (i = 0; i < (uint32_t) nsects; i++) {
coff_symbol(sects[i]->name, 0L, 0L, i + 1, 3, 1);
coff_symbol(sects[i]->name, 0L, 0L, i + 1, 0, 3, 1);
fwriteint32_t(sects[i]->len, coffp);
fwriteint16_t(sects[i]->nrelocs, coffp);
fwrite(filename, 12, 1, coffp);
@ -853,7 +918,7 @@ static void coff_write_symbols(void)
/*
* The absolute symbol, for relative-to-absolute relocations.
*/
coff_symbol(".absolut", 0L, 0L, -1, 3, 0);
coff_symbol(".absolut", 0L, 0L, -1, 0, 3, 0);
/*
* The real symbols.
@ -863,7 +928,7 @@ static void coff_write_symbols(void)
struct Symbol *sym = saa_rstruct(syms);
coff_symbol(sym->strpos == -1 ? sym->name : NULL,
sym->strpos, sym->value, sym->section,
sym->is_global ? 2 : 3, 0);
sym->type, sym->is_global ? 2 : 3, 0);
}
}
@ -891,6 +956,9 @@ static const char *coff_stdmac[] = {
"%imacro export 1+.nolist",
"[export %1]",
"%endmacro",
"%imacro safeseh 1.nolist",
"[safeseh %1]",
"%endmacro",
NULL
};