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liblink: warn about TLS base MRC instruction that does not write into R0.

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While we're here, make it lookup the tlsfallback symbol only once.

LGTM=crawshaw
R=golang-codereviews, crawshaw, dave
CC=golang-codereviews
https://golang.org/cl/107430044
This commit is contained in:
Shenghou Ma 2014-07-26 17:46:51 -04:00
parent faa223459a
commit 20a5de9eb6
1 changed files with 20 additions and 12 deletions
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32
src/liblink/obj5.c
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@ -92,7 +92,7 @@ progedit(Link *ctxt, Prog *p)
{
char literal[64];
LSym *s;
LSym *tlsfallback;
static LSym *tlsfallback;
p->from.class = 0;
p->to.class = 0;
@ -111,19 +111,27 @@ progedit(Link *ctxt, Prog *p)
// Replace TLS register fetches on older ARM procesors.
switch(p->as) {
case AMRC:
// If the instruction matches MRC 15, 0, <reg>, C13, C0, 3, replace it.
if(ctxt->goarm < 7 && (p->to.offset & 0xffff0fff) == 0xee1d0f70) {
tlsfallback = linklookup(ctxt, "runtime.read_tls_fallback", 0);
// Treat MRC 15, 0, <reg>, C13, C0, 3 specially.
if((p->to.offset & 0xffff0fff) == 0xee1d0f70) {
// Because the instruction might be rewriten to a BL which returns in R0
// the register must be zero.
if ((p->to.offset & 0xf000) != 0)
ctxt->diag("%L: TLS MRC instruction must write to R0 as it might get translated into a BL instruction", p->lineno);
// BL runtime.read_tls_fallback(SB)
p->as = ABL;
p->to.type = D_BRANCH;
p->to.sym = tlsfallback;
p->to.offset = 0;
} else {
// Otherwise, MRC/MCR instructions need no further treatment.
p->as = AWORD;
if(ctxt->goarm < 7) {
// Replace it with BL runtime.read_tls_fallback(SB).
if(tlsfallback == nil)
tlsfallback = linklookup(ctxt, "runtime.read_tls_fallback", 0);
// BL runtime.read_tls_fallback(SB)
p->as = ABL;
p->to.type = D_BRANCH;
p->to.sym = tlsfallback;
p->to.offset = 0;
break;
}
}
// Otherwise, MRC/MCR instructions need no further treatment.
p->as = AWORD;
break;
}