Thread suspension: Implement for Linux

src/trusted/service_runtime/arch/x86_32/nacl_tls_32.c

Index: src/trusted/service_runtime/arch/x86_32/nacl_tls_32.c
diff --git a/src/trusted/service_runtime/arch/x86_32/nacl_tls_32.c b/src/trusted/service_runtime/arch/x86_32/nacl_tls_32.c
index 5f3d516634dc749a2f0b56cb87dbe2d62db92fe9..4b27c0fc2a195c4b56c5594d127c0fb0d14ac6f6 100644
--- a/src/trusted/service_runtime/arch/x86_32/nacl_tls_32.c
+++ b/src/trusted/service_runtime/arch/x86_32/nacl_tls_32.c
@@ -58,6 +58,30 @@ uint32_t NaClGetThreadIdx(struct NaClAppThread *natp) {
   return natp->user.gs >> 3;
 }
 
+#if NACL_LINUX
+
+/*
+ * This TLS variable mirrors nacl_thread_index in the x86-64 sandbox,
+ * except that, on x86-32, we only use it for getting the identity of
+ * the interrupted thread in a signal handler in the Linux
+ * implementation of thread suspension.
+ *
+ * We should not enable this code on Windows because TLS variables do
+ * not work inside dynamically-loaded DLLs -- such as chrome.dll -- on
+ * Windows XP.
+ */
+THREAD uint32_t nacl_thread_index;
+
+void NaClTlsSetIdx(uint32_t tls_idx) {
+  nacl_thread_index = tls_idx;
+}
+
+uint32_t NaClTlsGetIdx(void) {
+  return nacl_thread_index;
+}
+
+#else
+
 /*
  * This is a NOOP, since TLS (or TSD) is not used to keep the thread
  * index on the x86-32.  We use segmentation (%gs) to provide access

[bradn, 2012/05/18 19:56:35]

This comment and the one above are starting to feel misleading.
Maybe collapse into a single comment describing the 3 cases of use:
linux32 - just for signal handler
x86-64 - generally
x86-32 (non-linux) - not

Given how fickle using gs is (and all the random asm that also uses it), I can't
help but wonder if we should move to using this one in more places. Just
thinking, no real change here.

[Mark Seaborn, 2012/05/21 15:03:57]

We discussed this and you were OK with the current comments.  The comments are
applicable to the #ifs they are inside.

@@ -67,3 +91,5 @@ uint32_t NaClGetThreadIdx(struct NaClAppThread *natp) {
 void NaClTlsSetIdx(uint32_t tls_idx) {
   UNREFERENCED_PARAMETER(tls_idx);
 }
+
+#endif