From 2349c3dbde77ea7ef32a89eea2c09048d93c671e Mon Sep 17 00:00:00 2001
From: Robert Hensing <robert@roberthensing.nl>
Date: Wed, 15 Oct 2025 22:40:31 +0200
Subject: [PATCH] setStackSize: Warn when the desired stack size can't be set

---
 src/libutil/current-process.cc | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/src/libutil/current-process.cc b/src/libutil/current-process.cc
index 988621014..10522d5ae 100644
--- a/src/libutil/current-process.cc
+++ b/src/libutil/current-process.cc
@@ -65,6 +65,16 @@ void setStackSize(size_t stackSize)
     struct rlimit limit;
     if (getrlimit(RLIMIT_STACK, &limit) == 0 && static_cast<size_t>(limit.rlim_cur) < stackSize) {
         savedStackSize = limit.rlim_cur;
+        if (limit.rlim_max < static_cast<rlim_t>(stackSize)) {
+            logger->log(
+                lvlWarn,
+                HintFmt(
+                    "Stack size hard limit is %1%, which is less than the desired %2%. If possible, increase the hard limit, e.g. with 'ulimit -Hs %3%'.",
+                    limit.rlim_max,
+                    stackSize,
+                    stackSize / 1024)
+                    .str());
+        }
         auto requestedSize = std::min(static_cast<rlim_t>(stackSize), limit.rlim_max);
         limit.rlim_cur = requestedSize;
         if (setrlimit(RLIMIT_STACK, &limit) != 0) {