[CRIU] [PATCH RFC] compel: Save thread registers before executing parasite code

[Michael Holzheu]

For dumping threads we execute parasite code before we collect the
floating point registers with get_task_regs().

The following describes the code path were this is done:

 dump_task_threads()
     for (i = 0; i < item->nr_threads; i++)
         dump_task_thread()
           parasite_dump_thread_seized()
             compel_prepare_thread()
                prepare_thread()

                   ### Get general purpose registers ###
                   ptrace_get_regs(ctx->regs)

             ### Parasite code is executed in thread ###
             compel_run_in_thread(tctl, PARASITE_CMD_DUMP_THREAD)

             compel_get_thread_regs()

                 ### Get FP and VX registers ###
                 get_task_regs()

On s390 gcc uses floating point registers to cache general purpose
registers. Therefore we use the -msoft-float option to ensure that
floating point registers are not clobbered in compel_run_in_thread().

There might be a better option:

First save the thread registers and then call the parasite code. This
allows us to remove the -msoft-float on s390.

Signed-off-by: Michael Holzheu <holzheu at linux.vnet.ibm.com>
---
 Makefile.compel           |  4 ++--
 criu/parasite-syscall.c   | 11 +++++------
 criu/pie/Makefile         |  7 -------
 criu/pie/Makefile.library |  6 ------
 4 files changed, 7 insertions(+), 21 deletions(-)

diff --git a/Makefile.compel b/Makefile.compel
index 5c854e3..d200cb8 100644
--- a/Makefile.compel
+++ b/Makefile.compel
@@ -77,6 +77,6 @@ compel-install-targets	+= $(compel-plugins)
 # commit "S/390: Fix 64 bit sibcall".
 #
 ifeq ($(ARCH),s390)
-CFLAGS += -msoft-float -fno-optimize-sibling-calls
-HOSTCFLAGS += -msoft-float -fno-optimize-sibling-calls
+CFLAGS += -fno-optimize-sibling-calls
+HOSTCFLAGS += -fno-optimize-sibling-calls
 endif
diff --git a/criu/parasite-syscall.c b/criu/parasite-syscall.c
index 69dba60..76e943e 100644
--- a/criu/parasite-syscall.c
+++ b/criu/parasite-syscall.c
@@ -198,6 +198,11 @@ int parasite_dump_thread_seized(struct parasite_ctl *ctl, const struct pstree_it
 
 	tc->has_blk_sigset = true;
 	memcpy(&tc->blk_sigset, compel_thread_sigmask(tctl), sizeof(k_rtsigset_t));
+	ret = compel_get_thread_regs(tctl, save_task_regs, core);
+	if (ret) {
+		pr_err("Can't obtain regs for thread %d\n", pid);
+		goto err_rth;
+	}
 
 	ret = compel_run_in_thread(tctl, PARASITE_CMD_DUMP_THREAD);
 	if (ret) {
@@ -211,12 +216,6 @@ int parasite_dump_thread_seized(struct parasite_ctl *ctl, const struct pstree_it
 		goto err_rth;
 	}
 
-	ret = compel_get_thread_regs(tctl, save_task_regs, core);
-	if (ret) {
-		pr_err("Can't obtain regs for thread %d\n", pid);
-		goto err_rth;
-	}
-
 	compel_release_thread(tctl);
 
 	*parasite_tid = args->tid;
diff --git a/criu/pie/Makefile b/criu/pie/Makefile
index 76c3535..73d95d5 100644
--- a/criu/pie/Makefile
+++ b/criu/pie/Makefile
@@ -16,13 +16,6 @@ ifeq ($(SRCARCH),arm)
 	ccflags-y	+= -marm
 endif
 
-# We assume that compel code does not change floating point registers.
-# On s390 gcc uses fprs to cache gprs. Therefore disable floating point
-# with -msoft-float.
-ifeq ($(SRCARCH),s390)
-	ccflags-y	+= -msoft-float
-endif
-
 asflags-y	+= -D__ASSEMBLY__
 
 LDS		:= compel/arch/$(SRCARCH)/scripts/compel-pack.lds.S
diff --git a/criu/pie/Makefile.library b/criu/pie/Makefile.library
index ceadc1d..f589333 100644
--- a/criu/pie/Makefile.library
+++ b/criu/pie/Makefile.library
@@ -41,9 +41,3 @@ ccflags-y		+= $(COMPEL_UAPI_INCLUDES)
 ifeq ($(SRCARCH),arm)
 	ccflags-y	+= -marm
 endif
-# We assume that compel code does not change floating point registers.
-# On s390 gcc uses fprs to cache gprs. Therefore disable floating point
-# with -msoft-float.
-ifeq ($(SRCARCH),s390)
-	ccflags-y	+= -msoft-float
-endif
-- 
2.7.4