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tcg/arm: Clarify tcg_out_bx for arm4 host 

In theory this would re-enable usage of QEMU on an armv4 host.
Whether this is worthwhile is debatable -- we've been unconditionally
issuing the armv5t BX instruction in the prologue since 2011 without
complaint.  Possibly we should simply require an armv6 host.

Signed-off-by: Richard Henderson <rth@twiddle.net>
This commit is contained in:
Richard Henderson 2017-04-28 09:45:57 +02:00
parent 46644483ca
commit 702a947484
1 changed files with 15 additions and 14 deletions
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29
tcg/arm/tcg-target.inc.c
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@ -329,11 +329,6 @@ static const uint8_t tcg_cond_to_arm_cond[] = {
[TCG_COND_GTU] = COND_HI,
};
static inline void tcg_out_bx(TCGContext *s, int cond, int rn)
{
tcg_out32(s, (cond << 28) | 0x012fff10 | rn);
}
static inline void tcg_out_b(TCGContext *s, int cond, int32_t offset)
{
tcg_out32(s, (cond << 28) | 0x0a000000 |
@ -402,6 +397,18 @@ static inline void tcg_out_mov_reg(TCGContext *s, int cond, int rd, int rm)
}
}
static inline void tcg_out_bx(TCGContext *s, int cond, TCGReg rn)
{
/* Unless the C portion of QEMU is compiled as thumb, we don't
actually need true BX semantics; merely a branch to an address
held in a register. */
if (use_armv5t_instructions) {
tcg_out32(s, (cond << 28) | 0x012fff10 | rn);
} else {
tcg_out_mov_reg(s, cond, TCG_REG_PC, rn);
}
}
static inline void tcg_out_dat_imm(TCGContext *s,
int cond, int opc, int rd, int rn, int im)
{
@ -977,7 +984,7 @@ static inline void tcg_out_st8(TCGContext *s, int cond,
* with the code buffer limited to 16MB we wouldn't need the long case.
* But we also use it for the tail-call to the qemu_ld/st helpers, which does.
*/
static inline void tcg_out_goto(TCGContext *s, int cond, tcg_insn_unit *addr)
static void tcg_out_goto(TCGContext *s, int cond, tcg_insn_unit *addr)
{
intptr_t addri = (intptr_t)addr;
ptrdiff_t disp = tcg_pcrel_diff(s, addr);
@ -987,15 +994,9 @@ static inline void tcg_out_goto(TCGContext *s, int cond, tcg_insn_unit *addr)
return;
}
assert(use_armv5t_instructions || (addri & 1) == 0);
tcg_out_movi32(s, cond, TCG_REG_TMP, addri);
if (use_armv5t_instructions) {
tcg_out_bx(s, cond, TCG_REG_TMP);
} else {
if (addri & 1) {
tcg_abort();
}
tcg_out_mov_reg(s, cond, TCG_REG_PC, TCG_REG_TMP);
}
tcg_out_bx(s, cond, TCG_REG_TMP);
}
/* The call case is mostly used for helpers - so it's not unreasonable