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target/mips: Fix single stepping

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As per an ancient comment in mips_tr_translate_insn about the
expectations of gdb, when restarting the insn in a delay slot
we also re-execute the branch.  Which means that we are
expected to execute two insns in this case.

This has been broken since 8b86d6d258, where we forced max_insns
to 1 while single-stepping.  This resulted in an exit from the
translator loop after the branch but before the delay slot is
translated.

Increase the max_insns to 2 for this case.  In addition, bypass
the end-of-page check, for when the branch itself ends the page.

Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
This commit is contained in:
Richard Henderson 2021-07-19 14:01:49 -10:00
parent 6634558025
commit ef00cd4a22
1 changed files with 16 additions and 9 deletions
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25
target/mips/tcg/translate.c
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@ -16016,6 +16016,16 @@ static void mips_tr_init_disas_context(DisasContextBase *dcbase, CPUState *cs)
ctx->default_tcg_memop_mask = (ctx->insn_flags & (ISA_MIPS_R6 |
INSN_LOONGSON3A)) ? MO_UNALN : MO_ALIGN;
/*
* Execute a branch and its delay slot as a single instruction.
* This is what GDB expects and is consistent with what the
* hardware does (e.g. if a delay slot instruction faults, the
* reported PC is the PC of the branch).
*/
if (ctx->base.singlestep_enabled && (ctx->hflags & MIPS_HFLAG_BMASK)) {
ctx->base.max_insns = 2;
}
LOG_DISAS("\ntb %p idx %d hflags %04x\n", ctx->base.tb, ctx->mem_idx,
ctx->hflags);
}
@ -16085,17 +16095,14 @@ static void mips_tr_translate_insn(DisasContextBase *dcbase, CPUState *cs)
if (ctx->base.is_jmp != DISAS_NEXT) {
return;
}
/*
* Execute a branch and its delay slot as a single instruction.
* This is what GDB expects and is consistent with what the
* hardware does (e.g. if a delay slot instruction faults, the
* reported PC is the PC of the branch).
* End the TB on (most) page crossings.
* See mips_tr_init_disas_context about single-stepping a branch
* together with its delay slot.
*/
if (ctx->base.singlestep_enabled &&
(ctx->hflags & MIPS_HFLAG_BMASK) == 0) {
ctx->base.is_jmp = DISAS_TOO_MANY;
}
if (ctx->base.pc_next - ctx->page_start >= TARGET_PAGE_SIZE) {
if (ctx->base.pc_next - ctx->page_start >= TARGET_PAGE_SIZE
&& !ctx->base.singlestep_enabled) {
ctx->base.is_jmp = DISAS_TOO_MANY;
}
}