Use on_retract to fix detach on PPC64 stripped
There should still be a small window where this can fail, namely when we
catch IP in a stub, after address is read from .plt and moved to CTR, but
before it jumps there (which would get the process to breakpoint address,
which we now notice). We may need to either fixup the .plt[0], or do
code reading to figure out whether we are in a stub and compare CTR.
diff --git a/sysdeps/linux-gnu/ppc/plt.c b/sysdeps/linux-gnu/ppc/plt.c
index 57c3dc1..7a88714 100644
--- a/sysdeps/linux-gnu/ppc/plt.c
+++ b/sysdeps/linux-gnu/ppc/plt.c
@@ -727,10 +727,19 @@
}
static void
+jump_to_entry_point(struct Process *proc, struct breakpoint *bp)
+{
+ /* XXX The double cast should be removed when
+ * target_address_t becomes integral type. */
+ target_address_t rv = (target_address_t)
+ (uintptr_t)bp->libsym->arch.resolved_value;
+ set_instruction_pointer(proc, rv);
+}
+
+static void
ppc_plt_bp_continue(struct breakpoint *bp, struct Process *proc)
{
switch (bp->libsym->arch.type) {
- target_address_t rv;
struct Process *leader;
void (*on_all_stopped)(struct process_stopping_handler *);
enum callback_status (*keep_stepping_p)
@@ -768,11 +777,7 @@
return;
}
- /* XXX The double cast should be removed when
- * target_address_t becomes integral type. */
- rv = (target_address_t)
- (uintptr_t)bp->libsym->arch.resolved_value;
- set_instruction_pointer(proc, rv);
+ jump_to_entry_point(proc, bp);
continue_process(proc->pid);
return;
@@ -785,6 +790,47 @@
abort();
}
+/* When a process is in a PLT stub, it may have already read the data
+ * in .plt that we changed. If we detach now, it will jump to PLT
+ * entry and continue to the dynamic linker, where it will SIGSEGV,
+ * because zeroth .plt slot is not filled in prelinked binaries, and
+ * the dynamic linker needs that data. Moreover, the process may
+ * actually have hit the breakpoint already. This functions tries to
+ * detect both cases and do any fix-ups necessary to mend this
+ * situation. */
+static enum callback_status
+detach_task_cb(struct Process *task, void *data)
+{
+ struct breakpoint *bp = data;
+
+ if (get_instruction_pointer(task) == bp->addr) {
+ debug(DEBUG_PROCESS, "%d at %p, which is PLT slot",
+ task->pid, bp->addr);
+ jump_to_entry_point(task, bp);
+ return CBS_CONT;
+ }
+ return CBS_CONT;
+}
+
+static void
+ppc_plt_bp_retract(struct breakpoint *bp, struct Process *proc)
+{
+ /* On PPC64, we rewrite .plt with PLT entry addresses. This
+ * needs to be undone. Unfortunately, the program may have
+ * made decisions based on that value */
+ if (proc->e_machine == EM_PPC64
+ && bp->libsym != NULL
+ && bp->libsym->arch.type == PPC_PLT_RESOLVED) {
+ fprintf(stderr,
+ "unresolve PLT:%p .plt:%#"PRIx64" orig:%#"PRIx64"\n",
+ bp->addr, bp->libsym->arch.plt_slot_addr,
+ bp->libsym->arch.resolved_value);
+ each_task(proc->leader, NULL, detach_task_cb, bp);
+ unresolve_plt_slot(proc, bp->libsym->arch.plt_slot_addr,
+ bp->libsym->arch.resolved_value);
+ }
+}
+
void
arch_library_init(struct library *lib)
{
@@ -845,6 +891,7 @@
static struct bp_callbacks cbs = {
.on_continue = ppc_plt_bp_continue,
+ .on_retract = ppc_plt_bp_retract,
};
breakpoint_set_callbacks(bp, &cbs);
return 0;