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sim: Restore stack alignemnt

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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 298c2e5e4f
Author: YAMAMOTO Takashi <yamamoto@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 2335b69120
Author: Xiang Xiao <xiaoxiang@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 <xiaoxiang@xiaomi.com>
```
This commit is contained in:
YAMAMOTO Takashi 2021-04-19 09:17:07 +09:00 committed by Xiang Xiao
parent 64f46b7f7e
commit 7f307f9765
1 changed files with 12 additions and 1 deletions
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13
arch/sim/src/sim/up_initialstate.c
View File

@ -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;
}