From b0b4c3c7fab812b42d932d555601794d296a51d6 Mon Sep 17 00:00:00 2001
From: Stefan Kalkowski <stefan.kalkowski@genode-labs.com>
Date: Fri, 15 Jan 2016 15:48:20 +0100
Subject: [PATCH] noux: consider stack alignment constraints

The interim stack in a forked noux process has to consider the architecture
dependent stack alignment constraints.

Fix #1852
---
 repos/base/include/base/thread.h         | 9 ++-------
 repos/base/include/spec/arm/cpu/consts.h | 9 +++++----
 repos/base/include/spec/x86/cpu/consts.h | 7 +++++--
 repos/ports/src/lib/libc_noux/plugin.cc  | 4 ++--
 4 files changed, 14 insertions(+), 15 deletions(-)

diff --git a/repos/base/include/base/thread.h b/repos/base/include/base/thread.h
index 2c0f0939a5..3f8841b6b3 100644
--- a/repos/base/include/base/thread.h
+++ b/repos/base/include/base/thread.h
@@ -110,14 +110,9 @@ class Genode::Thread_base
 			/**
 			 * Top of stack
 			 *
-			 * The alignment matches an initial stack frame, which is
-			 * sufficient for the AMD64 ABI (stack top + adjustment is 16-byte
-			 * aligned).
+			 * The alignment constrains are enforced by the CPU-specific ABI.
 			 */
-			addr_t stack_top() const
-			{
-				return ((addr_t)_stack & ~0xf) - Abi::stack_adjustment();
-			}
+			addr_t stack_top() const { return Abi::stack_align((addr_t)_stack); }
 
 			/**
 			 * Ensure that the stack has a given size at the minimum
diff --git a/repos/base/include/spec/arm/cpu/consts.h b/repos/base/include/spec/arm/cpu/consts.h
index 7bcbc71be7..19a3bc5e42 100644
--- a/repos/base/include/spec/arm/cpu/consts.h
+++ b/repos/base/include/spec/arm/cpu/consts.h
@@ -18,11 +18,12 @@
 
 namespace Abi {
 
-	/**
-	 * On ARM a call (or branch) will not change the stack pointer, so we do not
-	 * need stack adjustment
+	/*
+	 * On ARM we align the stack top to 16-byte. As a call (or branch) will not
+	 * change the stack pointer, we need no further stack adjustment.
 	 */
-	static constexpr Genode::size_t stack_adjustment() { return 0; }
+	static Genode::addr_t stack_align(Genode::addr_t addr) {
+		return (addr & ~0xf); }
 
 	/**
 	 * Do ABI specific initialization to a freshly created stack
diff --git a/repos/base/include/spec/x86/cpu/consts.h b/repos/base/include/spec/x86/cpu/consts.h
index 3b7ccbf318..4c67311872 100644
--- a/repos/base/include/spec/x86/cpu/consts.h
+++ b/repos/base/include/spec/x86/cpu/consts.h
@@ -37,9 +37,12 @@ namespace X86 {
 namespace Abi {
 
 	/**
-	 * On x86 a call will result in a growth of the stack by machine word size
+	 * On x86, we align the stack top to 16 byte. As a call will result in
+	 * growth of the stack, we further adjust the stack-top address to comply
+	 * to the AMD64 ABI rule "stack top + adjustment is 16-byte aligned".
 	 */
-	static constexpr Genode::size_t stack_adjustment() { return sizeof(Genode::addr_t); }
+	static Genode::addr_t stack_align(Genode::addr_t addr) {
+		return (addr & ~0xf) - sizeof(Genode::addr_t); }
 
 	/**
 	 * Do ABI specific initialization to a freshly created stack
diff --git a/repos/ports/src/lib/libc_noux/plugin.cc b/repos/ports/src/lib/libc_noux/plugin.cc
index bd27ae1676..7c1dd81d35 100644
--- a/repos/ports/src/lib/libc_noux/plugin.cc
+++ b/repos/ports/src/lib/libc_noux/plugin.cc
@@ -564,8 +564,8 @@ extern "C" pid_t fork(void)
 		stack_in_context_area = &dummy;
 
 		/* got here during the normal control flow of the fork call */
-		sysio()->fork_in.ip              = (Genode::addr_t)(&fork_trampoline);
-		sysio()->fork_in.sp              = (Genode::addr_t)(&stack[STACK_SIZE]);
+		sysio()->fork_in.ip = (Genode::addr_t)(&fork_trampoline);
+		sysio()->fork_in.sp = Abi::stack_align((Genode::addr_t)&stack[STACK_SIZE]);
 		sysio()->fork_in.parent_cap_addr = (Genode::addr_t)(&new_parent);
 
 		if (!noux_syscall(Noux::Session::SYSCALL_FORK)) {