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Fix the insn position shown by rb_vm_check_canary #10062

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merged 1 commit into from
Feb 21, 2024
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Fix the insn position shown by rb_vm_check_canary #10062

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20 changes: 18 additions & 2 deletions vm_insnhelper.c
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Original file line number Diff line number Diff line change
Expand Up @@ -233,6 +233,23 @@ vm_check_frame(VALUE type,
static VALUE vm_stack_canary; /* Initialized later */
static bool vm_stack_canary_was_born = false;

// Return the index of the instruction right before the given PC.
// This is needed because insn_entry advances PC before the insn body.
static unsigned int
previous_insn_index(const rb_iseq_t *iseq, const VALUE *pc)
{
unsigned int pos = 0;
while (pos < ISEQ_BODY(iseq)->iseq_size) {
int opcode = rb_vm_insn_addr2opcode((void *)ISEQ_BODY(iseq)->iseq_encoded[pos]);
unsigned int next_pos = pos + insn_len(opcode);
if (ISEQ_BODY(iseq)->iseq_encoded + next_pos == pc) {
return pos;
}
pos = next_pos;
}
rb_bug("failed to find the previous insn");
}

void
rb_vm_check_canary(const rb_execution_context_t *ec, VALUE *sp)
{
Expand All @@ -259,8 +276,7 @@ rb_vm_check_canary(const rb_execution_context_t *ec, VALUE *sp)
}

const VALUE *orig = rb_iseq_original_iseq(iseq);
const VALUE *encoded = ISEQ_BODY(iseq)->iseq_encoded;
const ptrdiff_t pos = GET_PC() - encoded;
const ptrdiff_t pos = previous_insn_index(iseq, GET_PC());
const enum ruby_vminsn_type insn = (enum ruby_vminsn_type)orig[pos];
const char *name = insn_name(insn);
const VALUE iseqw = rb_iseqw_new(iseq);
Expand Down