csu: Add the prologue and epilogue to the _init and _fini on i386

Normally, modern unwinders uses Dwarf information to unwind stack,
however in case when the code is not annotated by Dwarf instructions,
unwinders fallbacks to a frame-pointer based algorithm.

That is allows libunwind to unwind stack from global constructors and
destructors. Also it makes gdb happy as it printed nonexistent frame
before.

Reviewed by:		kib, imp
Differential Revision:	https://reviews.freebsd.org/D40948

2 files changed, 10 insertions, 4 deletions

diff --git a/lib/csu/i386/crti.S b/lib/csu/i386/crti.S
index 77e4e77722d7..f5883db0ba0f 100644
--- a/lib/csu/i386/crti.S
+++ b/lib/csu/i386/crti.S
@@ -31,13 +31,17 @@ __FBSDID("$FreeBSD$");
 	.globl	_init
 	.type	_init,@function
 _init:
-	sub	$12,%esp	/* re-align stack pointer */
+	pushl	%ebp
+	movl	%esp,%ebp
+	subl	$8,%esp		/* re-align stack pointer */
 
 	.section .fini,"ax",@progbits
 	.align	4
 	.globl	_fini
 	.type	_fini,@function
 _fini:
-	sub	$12,%esp	/* re-align stack pointer */
+	pushl	%ebp
+	movl	%esp,%ebp
+	subl	$8,%esp		/* re-align stack pointer */
 
 	.section .note.GNU-stack,"",%progbits
diff --git a/lib/csu/i386/crtn.S b/lib/csu/i386/crtn.S
index 0264e22540f1..f223062bb787 100644
--- a/lib/csu/i386/crtn.S
+++ b/lib/csu/i386/crtn.S
@@ -27,11 +27,13 @@
 __FBSDID("$FreeBSD$");
 
 	.section .init,"ax",@progbits
-	add	$12,%esp
+	addl	$8,%esp
+	popl	%ebp
 	ret
 
 	.section .fini,"ax",@progbits
-	add	$12,%esp
+	addl	$8,%esp
+	popl	%ebp
 	ret
 
 	.section .note.GNU-stack,"",%progbits