From 7fdab09bca8ccb8323b262efb739b93047b30cd8 Mon Sep 17 00:00:00 2001
From: Guillaume Chatelet <gchatelet@google.com>
Date: Tue, 10 Dec 2024 10:32:52 +0000
Subject: [PATCH] Fix allocator bump in printf string allocation

Fixes #373.
---
 src/utils/list_cpu_features.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/utils/list_cpu_features.c b/src/utils/list_cpu_features.c
index a173f866..ee8875e3 100644
--- a/src/utils/list_cpu_features.c
+++ b/src/utils/list_cpu_features.c
@@ -148,7 +148,11 @@ static Node* CreatePrintfString(const char* format, ...) {
   const int written = vsnprintf(ptr, gBumpAllocator.size, format, arglist);
   va_end(arglist);
   if (written < 0 || written >= (int)gBumpAllocator.size) internal_error();
-  return CreateConstantString((char*)BA_Bump(written));
+  // `vsnprintf` does not set `\0` when no characters are to be written.
+  if (written == 0) gBumpAllocator.ptr = '\0';
+  // `vsnprintf` returns the number of printed characters excluding `\0`.
+  const int null_terminated_written = written + 1;
+  return CreateConstantString((char*)BA_Bump(null_terminated_written));
 }
 
 // Adds a string node.