[PATCH] D57924: [safestack] Move sysconf(_SC_PAGESIZE) back where it was before r351506

[Vitaly Buka via Phabricator via llvm-commits]

vitalybuka created this revision.
vitalybuka added a reviewer: eugenis.
Herald added projects: Sanitizers, LLVM.
Herald added a subscriber: Sanitizers.

3rd party sysconf interceptor may crash if it's called before unsafe_stack_setup
pageSize is used only for mmmap, which is going to round up it to page size anyway,
and for guard check in interceptor, which happens after sysconf().


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D57924

Files:
  compiler-rt/lib/safestack/safestack.cc


Index: compiler-rt/lib/safestack/safestack.cc
===================================================================
--- compiler-rt/lib/safestack/safestack.cc
+++ compiler-rt/lib/safestack/safestack.cc
@@ -83,7 +83,7 @@
 const unsigned kDefaultUnsafeStackSize = 0x2800000;
 
 /// Runtime page size obtained through sysconf
-unsigned pageSize;
+unsigned pageSize = 4096;
 
 // Per-thread unsafe stack information. It's not frequently accessed, so there
 // it can be kept out of the tcb in normal thread-local variables.
@@ -264,11 +264,9 @@
 __attribute__((constructor(0)))
 #endif
 void __safestack_init() {
-  pageSize = sysconf(_SC_PAGESIZE);
-
   // Determine the stack size for the main thread.
   size_t size = kDefaultUnsafeStackSize;
-  size_t guard = 4096;
+  size_t guard = pageSize;
 
   struct rlimit limit;
   if (getrlimit(RLIMIT_STACK, &limit) == 0 && limit.rlim_cur != RLIM_INFINITY)
@@ -276,8 +274,8 @@
 
   // Allocate unsafe stack for main thread
   void *addr = unsafe_stack_alloc(size, guard);
-
   unsafe_stack_setup(addr, size, guard);
+  pageSize = sysconf(_SC_PAGESIZE);
 
   // Setup the cleanup handler
   pthread_key_create(&thread_cleanup_key, thread_cleanup_handler);


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