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ld: reading of ELF object files

R=iant
CC=golang-dev
https://golang.org/cl/3507041
This commit is contained in:
Russ Cox 2010-12-08 13:52:59 -05:00
parent 7431a3165e
commit 4d8d6d5cda

822
src/cmd/ld/ldelf.c Normal file
View File

@ -0,0 +1,822 @@
/*
Derived from Plan 9 from User Space's src/libmach/elf.h, elf.c
http://code.swtch.com/plan9port/src/tip/src/libmach/
Copyright © 2004 Russ Cox.
Portions Copyright © 2008-2010 Google Inc.
Portions Copyright © 2010 The Go Authors.
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
*/
#include "l.h"
#include "lib.h"
#include "../ld/elf.h"
enum
{
ElfClassNone = 0,
ElfClass32,
ElfClass64,
ElfDataNone = 0,
ElfDataLsb,
ElfDataMsb,
ElfTypeNone = 0,
ElfTypeRelocatable,
ElfTypeExecutable,
ElfTypeSharedObject,
ElfTypeCore,
/* 0xFF00 - 0xFFFF reserved for processor-specific types */
ElfMachNone = 0,
ElfMach32100, /* AT&T WE 32100 */
ElfMachSparc, /* SPARC */
ElfMach386, /* Intel 80386 */
ElfMach68000, /* Motorola 68000 */
ElfMach88000, /* Motorola 88000 */
ElfMach486, /* Intel 80486, no longer used */
ElfMach860, /* Intel 80860 */
ElfMachMips, /* MIPS RS3000 */
ElfMachS370, /* IBM System/370 */
ElfMachMipsLe, /* MIPS RS3000 LE */
ElfMachParisc = 15, /* HP PA RISC */
ElfMachVpp500 = 17, /* Fujitsu VPP500 */
ElfMachSparc32Plus, /* SPARC V8+ */
ElfMach960, /* Intel 80960 */
ElfMachPower, /* PowerPC */
ElfMachPower64, /* PowerPC 64 */
ElfMachS390, /* IBM System/390 */
ElfMachV800 = 36, /* NEC V800 */
ElfMachFr20, /* Fujitsu FR20 */
ElfMachRh32, /* TRW RH-32 */
ElfMachRce, /* Motorola RCE */
ElfMachArm, /* ARM */
ElfMachAlpha, /* Digital Alpha */
ElfMachSH, /* Hitachi SH */
ElfMachSparc9, /* SPARC V9 */
ElfMachAmd64 = 62,
/* and the list goes on... */
ElfAbiNone = 0,
ElfAbiSystemV = 0, /* [sic] */
ElfAbiHPUX,
ElfAbiNetBSD,
ElfAbiLinux,
ElfAbiSolaris = 6,
ElfAbiAix,
ElfAbiIrix,
ElfAbiFreeBSD,
ElfAbiTru64,
ElfAbiModesto,
ElfAbiOpenBSD,
ElfAbiARM = 97,
ElfAbiEmbedded = 255,
/* some of sections 0xFF00 - 0xFFFF reserved for various things */
ElfSectNone = 0,
ElfSectProgbits,
ElfSectSymtab,
ElfSectStrtab,
ElfSectRela,
ElfSectHash,
ElfSectDynamic,
ElfSectNote,
ElfSectNobits,
ElfSectRel,
ElfSectShlib,
ElfSectDynsym,
ElfSectFlagWrite = 0x1,
ElfSectFlagAlloc = 0x2,
ElfSectFlagExec = 0x4,
/* 0xF0000000 are reserved for processor specific */
ElfSymBindLocal = 0,
ElfSymBindGlobal,
ElfSymBindWeak,
/* 13-15 reserved */
ElfSymTypeNone = 0,
ElfSymTypeObject,
ElfSymTypeFunc,
ElfSymTypeSection,
ElfSymTypeFile,
/* 13-15 reserved */
ElfSymShnNone = 0,
ElfSymShnAbs = 0xFFF1,
ElfSymShnCommon = 0xFFF2,
/* 0xFF00-0xFF1F reserved for processors */
/* 0xFF20-0xFF3F reserved for operating systems */
ElfProgNone = 0,
ElfProgLoad,
ElfProgDynamic,
ElfProgInterp,
ElfProgNote,
ElfProgShlib,
ElfProgPhdr,
ElfProgFlagExec = 0x1,
ElfProgFlagWrite = 0x2,
ElfProgFlagRead = 0x4,
ElfNotePrStatus = 1,
ElfNotePrFpreg = 2,
ElfNotePrPsinfo = 3,
ElfNotePrTaskstruct = 4,
ElfNotePrAuxv = 6,
ElfNotePrXfpreg = 0x46e62b7f /* for gdb/386 */
};
typedef struct ElfHdrBytes ElfHdrBytes;
typedef struct ElfSectBytes ElfSectBytes;
typedef struct ElfProgBytes ElfProgBytes;
typedef struct ElfSymBytes ElfSymBytes;
typedef struct ElfHdrBytes64 ElfHdrBytes64;
typedef struct ElfSectBytes64 ElfSectBytes64;
typedef struct ElfProgBytes64 ElfProgBytes64;
typedef struct ElfSymBytes64 ElfSymBytes64;
struct ElfHdrBytes
{
uchar ident[16];
uchar type[2];
uchar machine[2];
uchar version[4];
uchar entry[4];
uchar phoff[4];
uchar shoff[4];
uchar flags[4];
uchar ehsize[2];
uchar phentsize[2];
uchar phnum[2];
uchar shentsize[2];
uchar shnum[2];
uchar shstrndx[2];
};
struct ElfHdrBytes64
{
uchar ident[16];
uchar type[2];
uchar machine[2];
uchar version[4];
uchar entry[8];
uchar phoff[8];
uchar shoff[8];
uchar flags[4];
uchar ehsize[2];
uchar phentsize[2];
uchar phnum[2];
uchar shentsize[2];
uchar shnum[2];
uchar shstrndx[2];
};
struct ElfSectBytes
{
uchar name[4];
uchar type[4];
uchar flags[4];
uchar addr[4];
uchar off[4];
uchar size[4];
uchar link[4];
uchar info[4];
uchar align[4];
uchar entsize[4];
};
struct ElfSectBytes64
{
uchar name[4];
uchar type[4];
uchar flags[8];
uchar addr[8];
uchar off[8];
uchar size[8];
uchar link[4];
uchar info[4];
uchar align[8];
uchar entsize[8];
};
struct ElfSymBytes
{
uchar name[4];
uchar value[4];
uchar size[4];
uchar info; /* top4: bind, bottom4: type */
uchar other;
uchar shndx[2];
};
struct ElfSymBytes64
{
uchar name[4];
uchar info; /* top4: bind, bottom4: type */
uchar other;
uchar shndx[2];
uchar value[8];
uchar size[8];
};
typedef struct ElfSect ElfSect;
typedef struct ElfObj ElfObj;
typedef struct ElfSym ElfSym;
struct ElfSect
{
char *name;
uint32 type;
uint64 flags;
uint64 addr;
uint64 off;
uint64 size;
uint32 link;
uint32 info;
uint64 align;
uint64 entsize;
uchar *base;
Sym *sym;
};
struct ElfObj
{
Biobuf *f;
int64 base; // offset in f where ELF begins
int64 len; // length of ELF
int is64;
char *name;
Endian *e;
ElfSect *sect;
uint nsect;
char *shstrtab;
int nsymtab;
ElfSect *symtab;
ElfSect *symstr;
uint32 type;
uint32 machine;
uint32 version;
uint64 entry;
uint64 phoff;
uint64 shoff;
uint32 flags;
uint32 ehsize;
uint32 phentsize;
uint32 phnum;
uint32 shentsize;
uint32 shnum;
uint32 shstrndx;
};
struct ElfSym
{
char* name;
uint64 value;
uint64 size;
uchar bind;
uchar type;
uchar other;
uint16 shndx;
Sym* sym;
};
uchar ElfMagic[4] = { 0x7F, 'E', 'L', 'F' };
static ElfSect* section(ElfObj*, char*);
static int map(ElfObj*, ElfSect*);
static int readsym(ElfObj*, int i, ElfSym*);
static int reltype(char*, int, uchar*);
void
ldelf(Biobuf *f, char *pkg, int64 len, char *pn)
{
int32 base;
uint64 add, info;
char *name;
int i, j, rela, is64, n;
uchar hdrbuf[64];
uchar *p, *dp;
ElfHdrBytes *hdr;
ElfObj *obj;
ElfSect *sect, *rsect, *text, *data, *bss, *rodata;
ElfSym sym;
Endian *e;
Reloc *r, *rp;
Sym *s;
if(debug['v'])
Bprint(&bso, "%5.2f ldelf %s\n", cputime(), pn);
version++;
base = Boffset(f);
if(Bread(f, &hdrbuf, sizeof hdrbuf) != sizeof hdrbuf)
goto bad;
hdr = (ElfHdrBytes*)&hdrbuf;
if(memcmp(hdr->ident, ElfMagic, 4) != 0)
goto bad;
switch(hdr->ident[5]) {
case ElfDataLsb:
e = ≤
break;
case ElfDataMsb:
e = &be;
break;
default:
goto bad;
}
// read header
obj = mal(sizeof *obj);
obj->e = e;
obj->f = f;
obj->base = base;
obj->len = len;
obj->name = pn;
is64 = 0;
if(hdr->ident[4] == ElfClass64) {
ElfHdrBytes64* hdr;
is64 = 1;
hdr = (ElfHdrBytes64*)hdrbuf;
obj->type = e->e16(hdr->type);
obj->machine = e->e16(hdr->machine);
obj->version = e->e32(hdr->version);
obj->phoff = e->e64(hdr->phoff);
obj->shoff = e->e64(hdr->shoff);
obj->flags = e->e32(hdr->flags);
obj->ehsize = e->e16(hdr->ehsize);
obj->phentsize = e->e16(hdr->phentsize);
obj->phnum = e->e16(hdr->phnum);
obj->shentsize = e->e16(hdr->shentsize);
obj->shnum = e->e16(hdr->shnum);
obj->shstrndx = e->e16(hdr->shstrndx);
} else {
obj->type = e->e16(hdr->type);
obj->machine = e->e16(hdr->machine);
obj->version = e->e32(hdr->version);
obj->entry = e->e32(hdr->entry);
obj->phoff = e->e32(hdr->phoff);
obj->shoff = e->e32(hdr->shoff);
obj->flags = e->e32(hdr->flags);
obj->ehsize = e->e16(hdr->ehsize);
obj->phentsize = e->e16(hdr->phentsize);
obj->phnum = e->e16(hdr->phnum);
obj->shentsize = e->e16(hdr->shentsize);
obj->shnum = e->e16(hdr->shnum);
obj->shstrndx = e->e16(hdr->shstrndx);
}
obj->is64 = is64;
if(hdr->ident[6] != obj->version)
goto bad;
if(e->e16(hdr->type) != ElfTypeRelocatable) {
diag("%s: elf but not elf relocatable object");
return;
}
switch(thechar) {
default:
diag("%s: elf %s unimplemented", thestring);
return;
case '5':
if(e != &le || obj->machine != ElfMachArm || hdr->ident[4] != ElfClass32) {
diag("%s: elf object but not arm", pn);
return;
}
break;
case '6':
if(e != &le || obj->machine != ElfMachAmd64 || hdr->ident[4] != ElfClass64) {
diag("%s: elf object but not amd64", pn);
return;
}
break;
case '8':
if(e != &le || obj->machine != ElfMach386 || hdr->ident[4] != ElfClass32) {
diag("%s: elf object but not 386", pn);
return;
}
break;
}
// load section list into memory.
obj->sect = mal(obj->shnum*sizeof obj->sect[0]);
obj->nsect = obj->shnum;
for(i=0; i<obj->nsect; i++) {
if(Bseek(f, base+obj->shoff+i*obj->shentsize, 0) < 0)
goto bad;
sect = &obj->sect[i];
if(is64) {
ElfSectBytes64 b;
werrstr("short read");
if(Bread(f, &b, sizeof b) != sizeof b)
goto bad;
sect->name = (char*)(uintptr)e->e32(b.name);
sect->type = e->e32(b.type);
sect->flags = e->e64(b.flags);
sect->addr = e->e64(b.addr);
sect->off = e->e64(b.off);
sect->size = e->e64(b.size);
sect->link = e->e32(b.link);
sect->info = e->e32(b.info);
sect->align = e->e64(b.align);
sect->entsize = e->e64(b.entsize);
} else {
ElfSectBytes b;
werrstr("short read");
if(Bread(f, &b, sizeof b) != sizeof b)
goto bad;
sect->name = (char*)(uintptr)e->e32(b.name);
sect->type = e->e32(b.type);
sect->flags = e->e32(b.flags);
sect->addr = e->e32(b.addr);
sect->off = e->e32(b.off);
sect->size = e->e32(b.size);
sect->link = e->e32(b.link);
sect->info = e->e32(b.info);
sect->align = e->e32(b.align);
sect->entsize = e->e32(b.entsize);
}
}
// read section string table and translate names
if(obj->shstrndx >= obj->nsect) {
werrstr("shstrndx out of range %d >= %d", obj->shstrndx, obj->nsect);
goto bad;
}
sect = &obj->sect[obj->shstrndx];
if(map(obj, sect) < 0)
goto bad;
for(i=0; i<obj->nsect; i++)
if(obj->sect[i].name != nil)
obj->sect[i].name = (char*)sect->base + (uintptr)obj->sect[i].name;
// load string table for symbols into memory.
obj->symtab = section(obj, ".symtab");
if(obj->symtab == nil) {
diag("%s: elf object has no symbol table", pn);
return;
}
if(obj->symtab->link <= 0 || obj->symtab->link >= obj->nsect) {
diag("%s: elf object has symbol table with invalid string table link", pn);
return;
}
obj->symstr = &obj->sect[obj->symtab->link];
if(is64)
obj->nsymtab = obj->symtab->size / sizeof(ElfSymBytes64);
else
obj->nsymtab = obj->symtab->size / sizeof(ElfSymBytes);
if(map(obj, obj->symtab) < 0)
goto bad;
if(map(obj, obj->symstr) < 0)
goto bad;
// load text and data segments into memory.
// they are not as small as the section lists, but we'll need
// the memory anyway for the symbol images, so we might
// as well use one large chunk.
text = section(obj, ".text");
if(text && map(obj, text) < 0)
goto bad;
data = section(obj, ".data");
if(data && map(obj, data) < 0)
goto bad;
bss = section(obj, ".bss");
rodata = section(obj, ".rodata");
if(rodata && map(obj, rodata) < 0)
goto bad;
// create symbols for mapped sections
for(i=0; i<obj->nsect; i++) {
sect = &obj->sect[i];
if(sect->type != ElfSectProgbits || !(sect->flags&ElfSectFlagAlloc))
continue;
if(map(obj, sect) < 0)
goto bad;
name = smprint("%s(%s)", pn, sect->name);
s = lookup(name, version);
free(name);
switch(sect->flags&(ElfSectFlagAlloc|ElfSectFlagWrite|ElfSectFlagExec)) {
default:
werrstr("unexpected flags for ELF section %s", sect->name);
goto bad;
case ElfSectFlagAlloc:
s->type = SRODATA;
break;
case ElfSectFlagAlloc + ElfSectFlagWrite:
s->type = SDATA;
break;
case ElfSectFlagAlloc + ElfSectFlagExec:
s->type = STEXT;
break;
}
s->p = sect->base;
s->np = sect->size;
s->size = sect->size;
if(s->type == STEXT) {
if(etextp)
etextp->next = s;
else
textp = s;
etextp = s;
}
sect->sym = s;
}
// load relocations
for(i=0; i<obj->nsect; i++) {
rsect = &obj->sect[i];
if(rsect->type != ElfSectRela && rsect->type != ElfSectRel)
continue;
if(rsect->info >= obj->nsect || obj->sect[rsect->info].base == nil)
continue;
sect = &obj->sect[rsect->info];
if(map(obj, rsect) < 0)
goto bad;
rela = rsect->type == ElfSectRela;
n = rsect->size/(4+4*is64)/(2+rela);
r = mal(n*sizeof r[0]);
p = rsect->base;
dp = sect->base;
for(j=0; j<n; j++) {
add = 0;
rp = &r[j];
if(is64) {
// 64-bit rel/rela
rp->off = e->e64(p);
p += 8;
info = e->e64(p);
p += 8;
if(rela) {
add = e->e64(p);
p += 8;
}
} else {
// 32-bit rel/rela
rp->off = e->e32(p);
p += 4;
info = e->e32(p);
info = info>>8<<32 | (info&0xff); // convert to 64-bit info
p += 4;
if(rela) {
add = e->e32(p);
p += 4;
}
}
if(readsym(obj, info>>32, &sym) < 0)
goto bad;
if(sym.sym == nil) {
werrstr("reloc of invalid sym %s shndx=%d type=%d", sym.name, sym.shndx, sym.type);
goto bad;
}
rp->sym = sym.sym;
rp->type = reltype(pn, (uint32)info, &rp->siz);
if(rela)
rp->add = add;
else {
// load addend from image
if(rp->siz == 4)
rp->add = e->e32(sect->base+rp->off);
else if(rp->siz == 8)
rp->add = e->e64(sect->base+rp->off);
else
diag("invalid rela size %d", rp->siz);
}
}
qsort(r, n, sizeof r[0], rbyoff); // just in case
s = sect->sym;
s->r = r;
s->nr = n;
}
// enter sub-symbols into symbol table.
// symbol 0 is the null symbol.
for(i=1; i<obj->nsymtab; i++) {
if(readsym(obj, i, &sym) < 0)
goto bad;
if(sym.type != ElfSymTypeFunc && sym.type != ElfSymTypeObject && sym.type != ElfSymTypeNone)
continue;
if(sym.shndx == ElfSymShnCommon) {
s = sym.sym;
if(s->size < sym.size)
s->size = sym.size;
if(s->type == 0 || s->type == SXREF)
s->type = SBSS;
continue;
}
if(sym.shndx >= obj->nsect || sym.shndx == 0)
continue;
sect = obj->sect+sym.shndx;
if(sect->sym == nil) {
diag("%s: sym#%d: ignoring %s in section %d (type %d)", pn, i, sym.name, sym.shndx, sym.type);
continue;
}
s = sym.sym;
s->sub = sect->sym->sub;
sect->sym->sub = s;
s->type = sect->sym->type | SSUB;
s->dynimplib = nil; // satisfy dynimport
s->dynimpname = nil; // satisfy dynimport
s->value = sym.value;
s->size = sym.size;
s->outer = sect->sym;
if(sect->sym->type == STEXT) {
Prog *p;
if(s->text != P)
diag("%s: duplicate definition of %s", pn, s->name);
// build a TEXT instruction with a unique pc
// just to make the rest of the linker happy.
// TODO: this is too 6l-specific ?
p = prg();
p->as = ATEXT;
p->from.type = D_EXTERN;
p->from.sym = s;
p->from.scale = 7;
p->to.type = D_CONST;
p->link = nil;
p->pc = pc++;
s->text = p;
etextp->next = s;
etextp = s;
}
}
return;
bad:
diag("%s: malformed elf file: %r", pn);
}
static ElfSect*
section(ElfObj *obj, char *name)
{
int i;
for(i=0; i<obj->nsect; i++)
if(obj->sect[i].name && name && strcmp(obj->sect[i].name, name) == 0)
return &obj->sect[i];
return nil;
}
static int
map(ElfObj *obj, ElfSect *sect)
{
if(sect->base != nil)
return 0;
if(sect->off+sect->size > obj->len) {
werrstr("elf section past end of file");
return -1;
}
sect->base = mal(sect->size);
werrstr("short read");
if(Bseek(obj->f, obj->base+sect->off, 0) < 0 || Bread(obj->f, sect->base, sect->size) != sect->size)
return -1;
return 0;
}
static int
readsym(ElfObj *obj, int i, ElfSym *sym)
{
Sym *s;
if(i >= obj->nsymtab || i < 0) {
werrstr("invalid elf symbol index");
return -1;
}
if(obj->is64) {
ElfSymBytes64 *b;
b = (ElfSymBytes64*)(obj->symtab->base + i*sizeof *b);
sym->name = (char*)obj->symstr->base + obj->e->e32(b->name);
sym->value = obj->e->e64(b->value);
sym->size = obj->e->e64(b->size);
sym->shndx = obj->e->e16(b->shndx);
sym->bind = b->info>>4;
sym->type = b->info&0xf;
sym->other = b->other;
} else {
ElfSymBytes *b;
b = (ElfSymBytes*)(obj->symtab->base + i*sizeof *b);
sym->name = (char*)obj->symstr->base + obj->e->e32(b->name);
sym->value = obj->e->e32(b->value);
sym->size = obj->e->e32(b->size);
sym->shndx = obj->e->e16(b->shndx);
sym->bind = b->info>>4;
sym->type = b->info&0xf;
sym->other = b->other;
}
s = nil;
if(strcmp(sym->name, "_GLOBAL_OFFSET_TABLE_") == 0)
sym->name = ".got";
if(strcmp(sym->name, "__stack_chk_fail_local") == 0)
sym->other = 0; // rewrite hidden -> default visibility
switch(sym->type) {
case ElfSymTypeSection:
s = obj->sect[sym->shndx].sym;
break;
case ElfSymTypeObject:
case ElfSymTypeFunc:
case ElfSymTypeNone:
switch(sym->bind) {
case ElfSymBindGlobal:
if(sym->other != 2) {
s = lookup(sym->name, 0);
break;
}
// fall through
case ElfSymBindLocal:
s = lookup(sym->name, version);
break;
default:
werrstr("%s: invalid symbol binding %d", sym->name, sym->bind);
return -1;
}
break;
}
if(s != nil && s->type == 0 && sym->type != ElfSymTypeSection)
s->type = SXREF;
sym->sym = s;
return 0;
}
int
rbyoff(const void *va, const void *vb)
{
Reloc *a, *b;
a = (Reloc*)va;
b = (Reloc*)vb;
if(a->off < b->off)
return -1;
if(a->off > b->off)
return +1;
return 0;
}
#define R(x, y) ((x)|((y)<<24))
static int
reltype(char *pn, int elftype, uchar *siz)
{
switch(R(thechar, elftype)) {
default:
diag("%s: unknown relocation type %d; compiled without -fpic?", pn, elftype);
case R('6', R_X86_64_PC32):
case R('6', R_X86_64_PLT32):
case R('6', R_X86_64_GOTPCREL):
case R('8', R_386_32):
case R('8', R_386_PC32):
case R('8', R_386_GOT32):
case R('8', R_386_PLT32):
case R('8', R_386_GOTOFF):
case R('8', R_386_GOTPC):
*siz = 4;
break;
case R('6', R_X86_64_64):
*siz = 8;
break;
}
return 256+elftype;
}