Commit 702a9474 authored by Richard Henderson's avatar Richard Henderson
Browse files

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: default avatarRichard Henderson <rth@twiddle.net>
parent 46644483

tcg/arm/tcg-target.inc.c

+15 −14
Original line number Diff line number Diff line
@@ -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);

    }

}



/* The call case is mostly used for helpers - so it's not unreasonable