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[PATCH v2 13/23] target/mips: Fix single stepping
From: |
Richard Henderson |
Subject: |
[PATCH v2 13/23] target/mips: Fix single stepping |
Date: |
Tue, 12 Oct 2021 09:21:49 -0700 |
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 8b86d6d2580, 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.
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
target/mips/tcg/translate.c | 25 ++++++++++++++++---------
1 file changed, 16 insertions(+), 9 deletions(-)
diff --git a/target/mips/tcg/translate.c b/target/mips/tcg/translate.c
index 148afec9dc..f239f9ffc0 100644
--- a/target/mips/tcg/translate.c
+++ b/target/mips/tcg/translate.c
@@ -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;
}
}
--
2.25.1
- [PATCH v2 02/23] target/alpha: Drop checks for singlestep_enabled, (continued)
- [PATCH v2 02/23] target/alpha: Drop checks for singlestep_enabled, Richard Henderson, 2021/10/12
- [PATCH v2 03/23] target/avr: Drop checks for singlestep_enabled, Richard Henderson, 2021/10/12
- [PATCH v2 04/23] target/cris: Drop checks for singlestep_enabled, Richard Henderson, 2021/10/12
- [PATCH v2 05/23] target/hexagon: Drop checks for singlestep_enabled, Richard Henderson, 2021/10/12
- [PATCH v2 06/23] target/arm: Drop checks for singlestep_enabled, Richard Henderson, 2021/10/12
- [PATCH v2 07/23] target/hppa: Drop checks for singlestep_enabled, Richard Henderson, 2021/10/12
- [PATCH v2 09/23] target/i386: Drop check for singlestep_enabled, Richard Henderson, 2021/10/12
- [PATCH v2 11/23] target/microblaze: Check CF_NO_GOTO_TB for DISAS_JUMP, Richard Henderson, 2021/10/12
- [PATCH v2 13/23] target/mips: Fix single stepping,
Richard Henderson <=
- [PATCH v2 15/23] target/openrisc: Drop checks for singlestep_enabled, Richard Henderson, 2021/10/12
- [PATCH v2 10/23] target/m68k: Drop checks for singlestep_enabled, Richard Henderson, 2021/10/12
- [PATCH v2 12/23] target/microblaze: Drop checks for singlestep_enabled, Richard Henderson, 2021/10/12
- [PATCH v2 14/23] target/mips: Drop exit checks for singlestep_enabled, Richard Henderson, 2021/10/12
- [PATCH v2 17/23] target/riscv: Remove dead code after exception, Richard Henderson, 2021/10/12
- [PATCH v2 18/23] target/riscv: Remove exit_tb and lookup_and_goto_ptr, Richard Henderson, 2021/10/12