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tcg/i386: Make direct jump patching thread-safe

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Ensure direct jump patching in i386 is atomic by:
* naturally aligning a location of direct jump address;
* using atomic_read()/atomic_set() for code patching.

Backports commit 0d07abf05e98903c7faf204a9a90f7d45b7554dc from qemu
This commit is contained in:
Sergey Fedorov 2018-02-23 20:36:13 -05:00 committed by Lioncash
parent fffa27d269
commit 5eb2d6618f
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GPG key ID: 4E3C3CC1031BA9C7
2 changed files with 24 additions and 1 deletions
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2
qemu/include/exec/exec-all.h
View file

@ -307,7 +307,7 @@ void ppc_tb_set_jmp_target(uintptr_t jmp_addr, uintptr_t addr);
static inline void tb_set_jmp_target1(uintptr_t jmp_addr, uintptr_t addr)
{
/* patch the branch destination */
stl_le_p((void*)jmp_addr, addr - (jmp_addr + 4));
atomic_set((int32_t *)jmp_addr, addr - (jmp_addr + 4));
/* no need to flush icache explicitly */
}
#elif defined(__s390x__)

23
qemu/tcg/i386/tcg-target.inc.c
View file

@ -1149,6 +1149,21 @@ static void tcg_out_jmp(TCGContext *s, tcg_insn_unit *dest)
tcg_out_branch(s, 0, dest);
}
static void tcg_out_nopn(TCGContext *s, int n)
{
int i;
/* Emit 1 or 2 operand size prefixes for the standard one byte nop,
* "xchg %eax,%eax", forming "xchg %ax,%ax". All cores accept the
* duplicate prefix, and all of the interesting recent cores can
* decode and discard the duplicates in a single cycle.
*/
tcg_debug_assert(n >= 1);
for (i = 1; i < n; ++i) {
tcg_out8(s, 0x66);
}
tcg_out8(s, 0x90);
}
#if defined(CONFIG_SOFTMMU)
/* helper signature: helper_ret_ld_mmu(CPUState *env, target_ulong addr,
* int mmu_idx, uintptr_t ra)
@ -1878,6 +1893,14 @@ static inline void tcg_out_op(TCGContext *s, TCGOpcode opc,
case INDEX_op_goto_tb:
if (s->tb_jmp_offset) {
/* direct jump method */
int gap;
/* jump displacement must be aligned for atomic patching;
* see if we need to add extra nops before jump
*/
gap = tcg_pcrel_diff(s, (void*)QEMU_ALIGN_PTR_UP(s->code_ptr + 1, 4));
if (gap != 1) {
tcg_out_nopn(s, gap - 1);
}
tcg_out8(s, OPC_JMP_long); /* jmp im */
s->tb_jmp_offset[args[0]] = tcg_current_code_size(s);
tcg_out32(s, 0);