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Fix Thumb-1 BE32 execution and disassembly.

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Thumb-1 code has some issues in BE32 mode (as currently implemented). In
short, since bytes are swapped within words at load time for BE32
executables, this also swaps pairs of adjacent Thumb-1 instructions.

This patch un-swaps those pairs of instructions again, both for execution,
and for disassembly. (The previous version of the patch always read four
bytes in arm_read_memory_func and then extracted the proper two bytes,
in a probably misguided attempt to match the behaviour of actual hardware
as described by e.g. the ARM9TDMI TRM, section 3.3 "Endian effects for
instruction fetches". It's less complicated to just read the correct
two bytes though.)

Backports commit f7478a92dd9ee2276bfaa5b7317140d3f9d6a53b from qemu
This commit is contained in:
Julian Brown 2018-03-02 00:20:09 -05:00 committed by Lioncash
parent 1aedb26670
commit 58059c3a35
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GPG key ID: 4E3C3CC1031BA9C7
1 changed files with 9 additions and 1 deletions
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10
qemu/target/arm/arm_ldst.h
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@ -39,7 +39,15 @@ static inline uint32_t arm_ldl_code(CPUARMState *env, target_ulong addr,
static inline uint16_t arm_lduw_code(CPUARMState *env, target_ulong addr,
bool sctlr_b)
{
uint16_t insn = cpu_lduw_code(env, addr);
uint16_t insn;
#ifndef CONFIG_USER_ONLY
/* In big-endian (BE32) mode, adjacent Thumb instructions have been swapped
within each word. Undo that now. */
if (sctlr_b) {
addr ^= 2;
}
#endif
insn = cpu_lduw_code(env, addr);
if (bswap_code(sctlr_b)) {
return bswap16(insn);
}