seemingly working c++ exception support

a1402352 · Nickolai Zeldovich · 53d7ac6f · a1402352 · a1402352 · a1402352
--- a/kernel/boot.S
+++ b/kernel/boot.S
@@ -236,3 +236,8 @@ loadgdt:
 	movw %ax, %gs

        ret
+
+.section .eh_frame
+.globl __EH_FRAME_BEGIN__
+__EH_FRAME_BEGIN__:
+
--- a/kernel/cpprt.cc
+++ b/kernel/cpprt.cc
@@ -143,10 +143,20 @@ namespace __cxxabiv1 {
  void (*__unexpected_handler)() = cxx_unexpected;
 };

+static char malloc_buf[65536];
+static std::atomic<size_t> malloc_idx;
+
 extern "C" void* malloc(size_t);
 void*
 malloc(size_t n)
 {
+  if (n > PGSIZE) {
+    // libgcc_eh needs to allocate a large chunk of memory once
+    size_t myoff = atomic_fetch_add(&malloc_idx, n);
+    assert(myoff + n <= sizeof(malloc_buf));
+    return &malloc_buf[myoff];
+  }
+
  u64* p = (u64*) kmalloc(n+8, "cpprt malloc");
  *p = n;
  return p+1;
@@ -156,6 +166,9 @@ extern "C" void free(void*);
 void
 free(void* vp)
 {
+  if (vp >= malloc_buf && vp < malloc_buf + sizeof(malloc_buf))
+    return;
+
  u64* p = (u64*) vp;
  kmfree(p-1, p[-1]+8);
 }
@@ -210,3 +223,11 @@ __cxa_get_globals_fast(void)
 {
  return myproc()->__cxa_eh_global;
 }
+
+extern "C" void __register_frame(u8*);
+void
+initcpprt(void)
+{
+  extern u8 __EH_FRAME_BEGIN__[];
+  __register_frame(__EH_FRAME_BEGIN__);
+}
--- a/kernel/main.cc
+++ b/kernel/main.cc
@@ -37,6 +37,7 @@ void initlockstat(void);
 void initwq(void);
 void initsperf(void);
 void initidle(void);
+void initcpprt(void);
 void idleloop(void);

 static volatile int bstate;
@@ -131,6 +132,7 @@ cmain(u64 mbmagic, u64 mbaddr)
  bootothers();    // start other processors
  kpml4.e[0] = 0;  // don't need 1 GB identity mapping anymore
  lcr3(rcr3());
+  initcpprt();

  idleloop();