[incubator-nuttx] branch master updated: sim: Restore stack alignemnt

[xiaoxiang]

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xiaoxiang pushed a commit to branch master
in repository https://gitbox.apache.org/repos/asf/incubator-nuttx.git


The following commit(s) were added to refs/heads/master by this push:
     new 7f307f9  sim: Restore stack alignemnt
7f307f9 is described below

commit 7f307f976568cdb166161c93de0ec6024dc0c290
Author: YAMAMOTO Takashi <yamam...@midokura.com>
AuthorDate: Mon Apr 19 09:17:07 2021 +0900

    sim: Restore stack alignemnt
    
    Reapply the following commit [1], which has been reverted by
    the recent change [2] with no obvious reasons.
    
    Also, add a comment block to explain the calculation.
    
    [1]
    ```
    commit 298c2e5e4fb46f5ffa7de7bbc5a32a9da0663768
    Author: YAMAMOTO Takashi <yamam...@midokura.com>
    Date:   Wed Jan 29 03:26:43 2020 +0900
    
        sim: Fix stack alignment
    
        The recent x86-64 convention requires 16-byte alignment before
        (not after) calling a function.
    
        This fixes snprintf crash I observed on macOS while saving XMM 
registers.
    ```
    
    [2]
    ```
    commit 2335b69120a3e36f1aa0cecc19c95208806cae54
    Author: Xiang Xiao <xiaoxi...@xiaomi.com>
    Date:   Mon Apr 12 23:44:08 2021 +0800
    
        arch: Allocate the space from the beginning in up_stack_frame
    
        arch: Allocate the space from the beginning in up_stack_frame
    
        and modify the affected portion:
        1.Correct the stack dump and check
        2.Allocate tls_info_s by up_stack_frame too
        3.Move the stack fork allocation from arch to sched
    
        Signed-off-by: Xiang Xiao <xiaoxi...@xiaomi.com>
    ```
---
 arch/sim/src/sim/up_initialstate.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/arch/sim/src/sim/up_initialstate.c 
b/arch/sim/src/sim/up_initialstate.c
index bca7c25..ca62360 100644
--- a/arch/sim/src/sim/up_initialstate.c
+++ b/arch/sim/src/sim/up_initialstate.c
@@ -60,7 +60,18 @@ void up_initial_state(struct tcb_s *tcb)
     }
 
   memset(&tcb->xcp, 0, sizeof(struct xcptcontext));
+
+  /* Note: The amd64 ABI requires 16-bytes alignment _before_ a function
+   * call.
+   * On the other hand, our way to set up and switch to a new context
+   * is basically a JUMP.
+   * Thus, we need to emulate the effect of a CALL here, by subtracting
+   * sizeof(xcpt_reg_t), which is the amount a CALL would move RSP to store
+   * the return address.
+   */
+
   tcb->xcp.regs[JB_SP] = (xcpt_reg_t)tcb->stack_base_ptr +
-                                     tcb->adj_stack_size;
+                                     tcb->adj_stack_size -
+                                     sizeof(xcpt_reg_t);
   tcb->xcp.regs[JB_PC] = (xcpt_reg_t)tcb->start;
 }