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liblink: introduce way to avoid pc-relative addressing

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For Solaris. Sigh.

LGTM=dave
R=aram, iant, dave
CC=golang-codereviews
https://golang.org/cl/129540043
This commit is contained in:
Russ Cox 2014-08-25 18:45:29 -04:00
parent 236cf308c2
commit 4516a60062
1 changed files with 31 additions and 4 deletions
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35
src/liblink/asm6.c
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@ -1535,6 +1535,19 @@ static Optab optab[] =
static Optab* opindex[ALAST+1];
static vlong vaddr(Link*, Addr*, Reloc*);
// isextern reports whether s describes an external symbol that must avoid pc-relative addressing.
// This happens on systems like Solaris that call .so functions instead of system calls.
// It does not seem to be necessary for any other systems. This is probably working
// around a Solaris-specific bug that should be fixed differently, but we don't know
// what that bug is. And this does fix it.
static int
isextern(LSym *s)
{
// All the Solaris dynamic imports from libc.so begin with "libc·", which
// the compiler rewrites to "libc." by the time liblink gets it.
return strncmp(s->name, "libc.", 5) == 0;
}
// single-instruction no-ops of various lengths.
// constructed by hand and disassembled with gdb to verify.
// see http://www.agner.org/optimize/optimizing_assembly.pdf for discussion.
@ -1932,6 +1945,8 @@ oclass(Link *ctxt, Addr *a)
switch(a->index) {
case D_EXTERN:
case D_STATIC:
if(a->sym != nil && isextern(a->sym))
return Yi32;
return Yiauto; // use pc-relative addressing
case D_AUTO:
case D_PARAM:
@ -2109,7 +2124,7 @@ oclass(Link *ctxt, Addr *a)
return Yi32; /* unsigned */
return Yi64;
}
return Yi32; /* TO DO: D_ADDR as Yi64 */
return Yi32;
case D_BRANCH:
return Ybr;
@ -2282,12 +2297,17 @@ vaddr(Link *ctxt, Addr *a, Reloc *r)
ctxt->diag("need reloc for %D", a);
sysfatal("reloc");
}
r->siz = 4; // TODO: 8 for external symbols
if(isextern(s)) {
r->siz = 4;
r->type = R_ADDR;
} else {
r->siz = 4;
r->type = R_PCREL;
}
r->off = -1; // caller must fill in
r->sym = s;
r->add = v;
v = 0;
r->type = R_PCREL;
if(s->type == STLSBSS) {
r->xadd = r->add - r->siz;
r->type = R_TLS;
@ -2327,6 +2347,13 @@ asmandsz(Link *ctxt, Addr *a, int r, int rex, int m64)
switch(t) {
default:
goto bad;
case D_EXTERN:
case D_STATIC:
if(!isextern(a->sym))
goto bad;
t = D_NONE;
v = vaddr(ctxt, a, &rel);
break;
case D_AUTO:
case D_PARAM:
t = D_SP;
@ -2386,7 +2413,7 @@ asmandsz(Link *ctxt, Addr *a, int r, int rex, int m64)
ctxt->rexflag |= (regrex[t] & Rxb) | rex;
if(t == D_NONE || (D_CS <= t && t <= D_GS) || t == D_TLS) {
if(t == D_NONE && (a->type == D_STATIC || a->type == D_EXTERN) || ctxt->asmode != 64) {
if((a->sym == nil || !isextern(a->sym)) && t == D_NONE && (a->type == D_STATIC || a->type == D_EXTERN) || ctxt->asmode != 64) {
*ctxt->andptr++ = (0 << 6) | (5 << 0) | (r << 3);
goto putrelv;
}