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liblink: generate MRC replacement in liblink, not tls_arm

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Fixes #8690.

This CL moves the save of LR around BL runtime.read_tls_fallback to liblink as it is not needed when MRC is not replaced.

LGTM=rsc, minux
R=rsc, khr, minux
CC=golang-codereviews
https://golang.org/cl/147310043
This commit is contained in:
Dave Cheney 2014-09-30 10:03:10 +10:00
parent 5368e63b57
commit 0b36211cfb
2 changed files with 21 additions and 10 deletions
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20
src/liblink/obj5.c
View File

@ -119,14 +119,30 @@ progedit(Link *ctxt, Prog *p)
ctxt->diag("%L: TLS MRC instruction must write to R0 as it might get translated into a BL instruction", p->lineno);
if(ctxt->goarm < 7) {
// Replace it with BL runtime.read_tls_fallback(SB).
// Replace it with BL runtime.read_tls_fallback(SB) for ARM CPUs that lack the tls extension.
if(tlsfallback == nil)
tlsfallback = linklookup(ctxt, "runtime.read_tls_fallback", 0);
// BL runtime.read_tls_fallback(SB)
// MOVW LR, R11
p->as = AMOVW;
p->from.type = D_REG;
p->from.reg = REGLINK;
p->to.type = D_REG;
p->to.reg = REGTMP;
// BL runtime.read_tls_fallback(SB)
p = appendp(ctxt, p);
p->as = ABL;
p->to.type = D_BRANCH;
p->to.sym = tlsfallback;
p->to.offset = 0;
// MOVW R11, LR
p = appendp(ctxt, p);
p->as = AMOVW;
p->from.type = D_REG;
p->from.reg = REGTMP;
p->to.type = D_REG;
p->to.reg = REGLINK;
break;
}
}

11
src/runtime/tls_arm.s
View File

@ -31,11 +31,8 @@ TEXT runtime·save_g(SB),NOSPLIT,$-4
#endif
// If the host does not support MRC the linker will replace it with
// a call to runtime.read_tls_fallback which jumps to __kuser_get_tls.
// Both functions are written to only disturb R0 so it should be safe to
// use R11 here to temporarily store LR.
MOVW LR, R11
// The replacement function saves LR in R11 over the call to read_tls_fallback.
MRC 15, 0, R0, C13, C0, 3 // fetch TLS base pointer
MOVW R11, LR
// $runtime.tlsg(SB) is a special linker symbol.
// It is the offset from the TLS base pointer to our
// thread-local storage for g.
@ -57,10 +54,8 @@ TEXT runtime·load_g(SB),NOSPLIT,$0
// nothing to do as nacl/arm does not use TLS at all.
RET
#endif
// See comment in save_g.
MOVW LR, R11
MRC 15, 0, R0, C13, C0, 3 // fetch TLS base pointer
MOVW R11, LR
// See save_g
MRC 15, 0, R0, C13, C0, 3 // fetch TLS base pointer
// $runtime.tlsg(SB) is a special linker symbol.
// It is the offset from the TLS base pointer to our
// thread-local storage for g.