fix integer overflow on i686 with high phys memory

sizeof(long) is 4 bytes on i686 GCC.
With ~32 GiB of memory and a page size of 4096, there are 7988420 pages.
(7988420 * 4096) is bigger than INT32_MAX folks.

This has gone unnoticed for 9 years, and only came up thanks to
94ea517db[1] adding integer overflow sensitization checks, which caused
this broken code to emit an illegal instruction, crashing Lix the
instant the buildsystem ran Lix to generate the docs files.

[1]: 94ea517dbe729765b69638190f4bea3f6a632b40

Change-Id: I50bb9ea072aac11b449d79e5d55525887a6e5a99

1 files changed, 6 insertions, 5 deletions

diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index b24f10c24..65f0a7938 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -316,13 +316,14 @@ void initGC()
        (resident) memory to be allocated.  This might be a problem on
        systems that don't overcommit. */
     if (!getEnv("GC_INITIAL_HEAP_SIZE")) {
-        size_t size = 32 * 1024 * 1024;
+        int64_t size = 32 * 1024 * 1024;
 #if HAVE_SYSCONF && defined(_SC_PAGESIZE) && defined(_SC_PHYS_PAGES)
-        size_t maxSize = 384 * 1024 * 1024;
-        long pageSize = sysconf(_SC_PAGESIZE);
-        long pages = sysconf(_SC_PHYS_PAGES);
-        if (pageSize != -1)
+        int64_t maxSize = 384 * 1024 * 1024;
+        int64_t pageSize = sysconf(_SC_PAGESIZE);
+        int64_t pages = sysconf(_SC_PHYS_PAGES);
+        if (pageSize != -1) {
             size = (pageSize * pages) / 4; // 25% of RAM
+        }
         if (size > maxSize) size = maxSize;
 #endif
         debug("setting initial heap size to %1% bytes", size);