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-rw-r--r--subx/012elf.cc1
1 files changed, 1 insertions, 0 deletions
diff --git a/subx/012elf.cc b/subx/012elf.cc
index d0a3fbd2..a77c6056 100644
--- a/subx/012elf.cc
+++ b/subx/012elf.cc
@@ -90,6 +90,7 @@ void load_elf_contents(uint8_t* elf_contents, size_t size, int argc, char* argv[
 
 void push(uint32_t val) {
   Reg[ESP].u -= 4;
+  assert(Reg[ESP].u >= STACK_SEGMENT);
   trace(Callstack_depth+1, "run") << "decrementing ESP to 0x" << HEXWORD << Reg[ESP].u << end();
   trace(Callstack_depth+1, "run") << "pushing value 0x" << HEXWORD << val << end();
   write_mem_u32(Reg[ESP].u, val);