[PATCH 3/3] gc: Pass register state to gc_start() and gc_safepoint()

[Pekka Enberg]

Save registers in gc_alloc() and pass them to gc_safepoint() so the
latter can scan them for references. Also save the registers in signal
handler and pass them to gc_safepoint(). We need to use pre-allocated
thread-local memory because we can't use the stack or malloc() in the
signal handler.

Cc: Tomek Grabiec <tgrab...@gmail.com>
Cc: Vegard Nossum <vegard.nos...@gmail.com>
Signed-off-by: Pekka Enberg <penb...@cs.helsinki.fi>
---
 include/vm/gc.h |    6 ++++--
 vm/gc.c         |   11 ++++++++---
 vm/signal.c     |    8 +++++++-
 3 files changed, 19 insertions(+), 6 deletions(-)

diff --git a/include/vm/gc.h b/include/vm/gc.h
index 343e04d..3b5889e 100644
--- a/include/vm/gc.h
+++ b/include/vm/gc.h
@@ -3,6 +3,8 @@
 
 #include <stdbool.h>
 
+struct register_state;
+
 extern void *gc_safepoint_page;
 extern bool verbose_gc;
 extern bool gc_enabled;
@@ -14,7 +16,7 @@ void *gc_alloc(size_t size);
 void gc_attach_thread(void);
 void gc_detach_thread(void);
 
-void gc_start(void);
-void gc_safepoint(void);
+void gc_start(struct register_state *);
+void gc_safepoint(struct register_state *);
 
 #endif
diff --git a/vm/gc.c b/vm/gc.c
index 93374bc..76bc5b9 100644
--- a/vm/gc.c
+++ b/vm/gc.c
@@ -3,6 +3,7 @@
 #include <stdio.h>
 #include <pthread.h>
 
+#include "arch/registers.h"
 #include "lib/guard-page.h"
 #include "vm/thread.h"
 #include "vm/stdlib.h"
@@ -34,8 +35,12 @@ void gc_init(void)
 
 void *gc_alloc(size_t size)
 {
+       struct register_state regs;
+
+       save_registers(&regs);
+
        if (gc_enabled)
-               gc_start();
+               gc_start(&regs);
 
        return zalloc(size);
 }
@@ -94,7 +99,7 @@ static void do_gc_safepoint(void)
        --nr_in_safepoint;
 }
 
-void gc_safepoint(void)
+void gc_safepoint(struct register_state *regs)
 {
        pthread_mutex_lock(&safepoint_mutex);
 
@@ -108,7 +113,7 @@ void gc_safepoint(void)
 /*
  * This is the main entrypoint to the stop-the-world GC.
  */
-void gc_start(void)
+void gc_start(struct register_state *regs)
 {
        pthread_mutex_lock(&safepoint_mutex);
 
diff --git a/vm/signal.c b/vm/signal.c
index 094fec6..63fe0d9 100644
--- a/vm/signal.c
+++ b/vm/signal.c
@@ -43,6 +43,8 @@
 #include <unistd.h>
 #include <stdio.h>
 
+static __thread struct register_state thread_register_state;
+
 static unsigned long throw_arithmetic_exception(unsigned long src_addr)
 {
        signal_new_exception(vm_java_lang_ArithmeticException,
@@ -76,7 +78,8 @@ static unsigned long rethrow_bh(unsigned long src_addr)
 
 static unsigned long gc_safepoint_bh(unsigned long addr)
 {
-       gc_safepoint();
+       gc_safepoint(&thread_register_state);
+
        return addr;
 }
 
@@ -118,6 +121,9 @@ static void sigsegv_handler(int sig, siginfo_t *si, void 
*ctx)
 
        /* Garbage collection safepoint */
        if (si->si_addr == gc_safepoint_page) {
+               ucontext_t *uc = ctx;
+
+               save_signal_registers(&thread_register_state, 
uc->uc_mcontext.gregs);
                install_signal_bh(ctx, gc_safepoint_bh);
                return;
        }
-- 
1.5.6.3


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