From bcd9614380f726cb689f3bb618426e9554c096ac Mon Sep 17 00:00:00 2001
From: Simon McVittie <smcv@collabora.com>
Date: Wed, 16 Oct 2024 17:40:13 +0100
Subject: [PATCH] utils: Add a fallback version of xadd, xmul for ancient gcc

bubblewrap is used in some surprisingly old environments, including
version 1 of the Steam Runtime, which has gcc 4.6 or 4.8 as its
default compiler (depending on exactly how you define "default").
These very old versions don't support the builtin used here.

Signed-off-by: Simon McVittie <smcv@collabora.com>
---
 utils.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/utils.c b/utils.c
index 3f008df3..985173e7 100644
--- a/utils.c
+++ b/utils.c
@@ -959,10 +959,17 @@ mount_strerror (int errsv)
 static size_t
 xadd (size_t a, size_t b)
 {
+#if defined(__GNUC__) && __GNUC__ >= 5
   size_t result;
   if (__builtin_add_overflow (a, b, &result))
     die_oom ();
   return result;
+#else
+  if (a > SIZE_MAX - b)
+    die_oom ();
+
+  return a + b;
+#endif
 }
 
 /*
@@ -972,10 +979,17 @@ xadd (size_t a, size_t b)
 static size_t
 xmul (size_t a, size_t b)
 {
+#if defined(__GNUC__) && __GNUC__ >= 5
   size_t result;
   if (__builtin_mul_overflow (a, b, &result))
     die_oom ();
   return result;
+#else
+  if (b != 0 && a > SIZE_MAX / b)
+    die_oom ();
+
+  return a * b;
+#endif
 }
 
 void