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// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Runtime symbol table access. Work in progress.
// The Plan 9 symbol table is not in a particularly convenient form.
// The routines here massage it into a more usable form; eventually
// we'll change 6l to do this for us, but it is easier to experiment
// here than to change 6l and all the other tools.
//
// The symbol table also needs to be better integrated with the type
// strings table in the future. This is just a quick way to get started
// and figure out exactly what we want.
#include "runtime.h"
// TODO(rsc): Move this *under* the text segment.
// Then define names for these addresses instead of hard-coding magic ones.
#ifdef _64BIT
#define SYMCOUNTS ((int32*)(0x99LL<<32)) // known to 6l
#define SYMDATA ((byte*)(0x99LL<<32) + 8)
#else
#define SYMCOUNTS ((int32*)(0x99LL<<24)) // known to 8l
#define SYMDATA ((byte*)(0x99LL<<24) + 8)
#endif
// Return a pointer to a byte array containing the symbol table segment.
void
sysยทsymdat(Array *symtab, Array *pclntab)
{
Array *a;
int32 *v;
v = SYMCOUNTS;
a = mal(sizeof *a);
a->nel = v[0];
a->cap = a->nel;
a->array = SYMDATA;
symtab = a;
FLUSH(&symtab);
a = mal(sizeof *a);
a->nel = v[1];
a->cap = a->nel;
a->array = SYMDATA + v[0];
pclntab = a;
FLUSH(&pclntab);
}
typedef struct Sym Sym;
struct Sym
{
uintptr value;
byte symtype;
byte *name;
byte *gotype;
};
// Walk over symtab, calling fn(&s) for each symbol.
static void
walksymtab(void (*fn)(Sym*))
{
int32 *v;
byte *p, *ep, *q;
Sym s;
v = SYMCOUNTS;
p = SYMDATA;
ep = p + v[0];
while(p < ep) {
if(p + 7 > ep)
break;
s.value = ((uint32)p[0]<<24) | ((uint32)p[1]<<16) | ((uint32)p[2]<<8) | ((uint32)p[3]);
if(!(p[4]&0x80))
break;
s.symtype = p[4] & ~0x80;
p += 5;
s.name = p;
if(s.symtype == 'z' || s.symtype == 'Z') {
// path reference string - skip first byte,
// then 2-byte pairs ending at two zeros.
q = p+1;
for(;;) {
if(q+2 > ep)
return;
if(q[0] == '\0' && q[1] == '\0')
break;
q += 2;
}
p = q+2;
}else{
q = mchr(p, '\0', ep);
if(q == nil)
break;
p = q+1;
}
q = mchr(p, '\0', ep);
if(q == nil)
break;
s.gotype = p;
p = q+1;
fn(&s);
}
}
// Symtab walker; accumulates info about functions.
static Func *func;
static int32 nfunc;
static byte **fname;
static int32 nfname;
static void
dofunc(Sym *sym)
{
Func *f;
switch(sym->symtype) {
case 't':
case 'T':
if(strcmp(sym->name, (byte*)"etext") == 0)
break;
if(func == nil) {
nfunc++;
break;
}
f = &func[nfunc++];
f->name = gostring(sym->name);
f->entry = sym->value;
break;
case 'm':
if(nfunc > 0 && func != nil)
func[nfunc-1].frame = sym->value;
break;
case 'p':
if(nfunc > 0 && func != nil) {
f = &func[nfunc-1];
// args counts 32-bit words.
// sym->value is the arg's offset.
// don't know width of this arg, so assume it is 64 bits.
if(f->args < sym->value/4 + 2)
f->args = sym->value/4 + 2;
}
break;
case 'f':
if(fname == nil) {
if(sym->value >= nfname)
nfname = sym->value+1;
break;
}
fname[sym->value] = sym->name;
break;
}
}
// put together the path name for a z entry.
// the f entries have been accumulated into fname already.
static void
makepath(byte *buf, int32 nbuf, byte *path)
{
int32 n, len;
byte *p, *ep, *q;
if(nbuf <= 0)
return;
p = buf;
ep = buf + nbuf;
*p = '\0';
for(;;) {
if(path[0] == 0 && path[1] == 0)
break;
n = (path[0]<<8) | path[1];
path += 2;
if(n >= nfname)
break;
q = fname[n];
len = findnull(q);
if(p+1+len >= ep)
break;
if(p > buf && p[-1] != '/')
*p++ = '/';
mcpy(p, q, len+1);
p += len;
}
}
// walk symtab accumulating path names for use by pc/ln table.
// don't need the full generality of the z entry history stack because
// there are no includes in go (and only sensible includes in our c).
static void
dosrcline(Sym *sym)
{
static byte srcbuf[1000];
static String srcstring;
static int32 lno, incstart;
static int32 nf, nhist;
Func *f;
switch(sym->symtype) {
case 't':
case 'T':
if(strcmp(sym->name, (byte*)"etext") == 0)
break;
f = &func[nf++];
f->src = srcstring;
f->ln0 += lno;
break;
case 'z':
if(sym->value == 1) {
// entry for main source file for a new object.
makepath(srcbuf, sizeof srcbuf, sym->name+1);
srcstring = gostring(srcbuf);
lno = 0;
nhist = 0;
} else {
// push or pop of included file.
makepath(srcbuf, sizeof srcbuf, sym->name+1);
if(srcbuf[0] != '\0') {
if(nhist++ == 0)
incstart = sym->value;
}else{
if(--nhist == 0)
lno -= sym->value - incstart;
}
}
}
}
enum { PcQuant = 1 };
// Interpret pc/ln table, saving the subpiece for each func.
static void
splitpcln(void)
{
int32 line;
uintptr pc;
byte *p, *ep;
Func *f, *ef;
int32 *v;
// pc/ln table bounds
v = SYMCOUNTS;
p = SYMDATA;
p += v[0];
ep = p+v[1];
f = func;
ef = func + nfunc;
pc = func[0].entry; // text base
f->pcln.array = p;
f->pc0 = pc - PcQuant;
line = 0;
for(; p < ep; p++) {
if(f < ef && pc >= (f+1)->entry) {
f->pcln.nel = p - f->pcln.array;
f->pcln.cap = f->pcln.nel;
f++;
f->pcln.array = p;
f->pc0 = pc;
f->ln0 = line;
}
if(*p == 0) {
// 4 byte add to line
line += (p[1]<<24) | (p[2]<<16) | (p[3]<<8) | p[4];
p += 4;
} else if(*p <= 64) {
line += *p;
} else if(*p <= 128) {
line -= *p - 64;
} else {
pc += PcQuant*(*p - 129);
}
pc += PcQuant;
}
if(f < ef) {
f->pcln.nel = p - f->pcln.array;
f->pcln.cap = f->pcln.nel;
}
}
// Return actual file line number for targetpc in func f.
// (Source file is f->src.)
int32
funcline(Func *f, uint64 targetpc)
{
byte *p, *ep;
uintptr pc;
int32 line;
p = f->pcln.array;
ep = p + f->pcln.nel;
pc = f->pc0;
line = f->ln0;
for(; p < ep; p++) {
if(pc >= targetpc)
return line;
if(*p == 0) {
line += (p[1]<<24) | (p[2]<<16) | (p[3]<<8) | p[4];
p += 4;
} else if(*p <= 64) {
line += *p;
} else if(*p <= 128) {
line -= *p - 64;
} else {
pc += PcQuant*(*p - 129);
}
pc += PcQuant;
}
return line;
}
static void
buildfuncs(void)
{
extern byte etext[];
if(func != nil)
return;
// count funcs, fnames
nfunc = 0;
nfname = 0;
walksymtab(dofunc);
// initialize tables
func = mal((nfunc+1)*sizeof func[0]);
func[nfunc].entry = (uint64)etext;
fname = mal(nfname*sizeof fname[0]);
nfunc = 0;
walksymtab(dofunc);
// split pc/ln table by func
splitpcln();
// record src file and line info for each func
walksymtab(dosrcline);
}
Func*
findfunc(uintptr addr)
{
Func *f;
int32 nf, n;
if(func == nil)
buildfuncs();
if(nfunc == 0)
return nil;
if(addr < func[0].entry || addr >= func[nfunc].entry)
return nil;
// binary search to find func with entry <= addr.
f = func;
nf = nfunc;
while(nf > 0) {
n = nf/2;
if(f[n].entry <= addr && addr < f[n+1].entry)
return &f[n];
else if(addr < f[n].entry)
nf = n;
else {
f += n+1;
nf -= n+1;
}
}
// can't get here -- we already checked above
// that the address was in the table bounds.
// this can only happen if the table isn't sorted
// by address or if the binary search above is buggy.
prints("findfunc unreachable\n");
return nil;
}