On s390{,x}, r2 is scrambled after syscall entry

This was caught by system_call_params.exp test case:

   exe->mount("source", "target", "filesystemtype", 0, nil <unfinished ...>
   mount@SYS("", "target", "filesystemtype", 0, nil)                 = -2
   <... mount resumed>                                               = -1

Note how the first parameter disappears--r2 now holds syscall number
(21 in this case), and the original value is stored in orig_gpr2 in
save area.

1 files changed, 12 insertions, 5 deletions

diff --git a/sysdeps/linux-gnu/s390/fetch.c b/sysdeps/linux-gnu/s390/fetch.c
index 0b68dbc..4ad5951 100644
--- a/sysdeps/linux-gnu/s390/fetch.c
+++ b/sysdeps/linux-gnu/s390/fetch.c
@@ -23,6 +23,7 @@
 #include <sys/ucontext.h>
 #include <assert.h>
 #include <errno.h>
+#include <stdbool.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -61,7 +62,8 @@ s390x(struct fetch_context *ctx)
 }
 
 static int
-fetch_register_banks(struct process *proc, struct fetch_context *ctx)
+fetch_register_banks(struct process *proc, struct fetch_context *ctx,
+		     bool syscall_enter)
 {
 	ptrace_area parea;
 	parea.len = sizeof(ctx->regs);
@@ -72,15 +74,20 @@ fetch_register_banks(struct process *proc, struct fetch_context *ctx)
 			strerror(errno));
 		return -1;
 	}
+
+	if (syscall_enter)
+		ctx->regs.gprs[2] = ctx->regs.orig_gpr2;
+
 	return 0;
 }
 
 static int
-fetch_context_init(struct process *proc, struct fetch_context *context)
+fetch_context_init(struct process *proc, struct fetch_context *context,
+		   bool syscall_enter)
 {
 	context->greg = 2;
 	context->freg = 0;
-	return fetch_register_banks(proc, context);
+	return fetch_register_banks(proc, context, syscall_enter);
 }
 
 struct fetch_context *
@@ -89,7 +96,7 @@ arch_fetch_arg_init(enum tof type, struct process *proc,
 {
 	struct fetch_context *context = malloc(sizeof(*context));
 	if (context == NULL
-	    || fetch_context_init(proc, context) < 0) {
+	    || fetch_context_init(proc, context, type == LT_TOF_SYSCALL) < 0) {
 		fprintf(stderr, "arch_fetch_arg_init: %s\n",
 			strerror(errno));
 		free(context);
@@ -277,7 +284,7 @@ arch_fetch_retval(struct fetch_context *ctx, enum tof type,
 		return 0;
 	}
 
-	if (fetch_context_init(proc, ctx) < 0)
+	if (fetch_context_init(proc, ctx, false) < 0)
 		return -1;
 	return arch_fetch_arg_next(ctx, type, proc, info, valuep);
 }