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cmd/8l: fix data corruption for MULB SI,

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The 8l linker automatically inserts XCHG instructions
to support otherwise impossible byte registers
(only available on AX, BX, CX, DX).

Sometimes AX or DX is needed (for MUL and DIV) so
we need to avoid clobbering them.

R=golang-dev, dave, iant, iant, rsc
CC=golang-dev
https://golang.org/cl/6846057
This commit is contained in:
Rémy Oudompheng 2012-11-26 21:31:42 +01:00
parent af375cde20
commit 54023a94a6
2 changed files with 6 additions and 2 deletions
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4
src/cmd/6l/span.c
View File

@ -1618,7 +1618,9 @@ bad:
pp = *p; pp = *p;
z = p->from.type; z = p->from.type;
if(z >= D_BP && z <= D_DI) { if(z >= D_BP && z <= D_DI) {
if(isax(&p->to)) { if(isax(&p->to) || p->to.type == D_NONE) {
// We certainly don't want to exchange
// with AX if the op is MUL or DIV.
*andptr++ = 0x87; /* xchg lhs,bx */ *andptr++ = 0x87; /* xchg lhs,bx */
asmando(&p->from, reg[D_BX]); asmando(&p->from, reg[D_BX]);
subreg(&pp, z, D_BX); subreg(&pp, z, D_BX);

4
src/cmd/8l/span.c
View File

@ -1272,7 +1272,9 @@ bad:
pp = *p; pp = *p;
z = p->from.type; z = p->from.type;
if(z >= D_BP && z <= D_DI) { if(z >= D_BP && z <= D_DI) {
if(isax(&p->to)) { if(isax(&p->to) || p->to.type == D_NONE) {
// We certainly don't want to exchange
// with AX if the op is MUL or DIV.
*andptr++ = 0x87; /* xchg lhs,bx */ *andptr++ = 0x87; /* xchg lhs,bx */
asmand(&p->from, reg[D_BX]); asmand(&p->from, reg[D_BX]);
subreg(&pp, z, D_BX); subreg(&pp, z, D_BX);