audk/MdePkg/Library/BaseLib/Ebc/SetJumpLongJump.c

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/** @file
Implementation of SetJump() and LongJump() on EBC.
SetJump() and LongJump() are not currently supported for the EBC processor type.
Implementation for EBC just returns 0 for SetJump(), and ASSERT() for LongJump().
Copyright (c) 2006 - 2008, Intel Corporation. All rights reserved.<BR>
This program and the accompanying materials
are licensed and made available under the terms and conditions of the BSD License
which accompanies this distribution. The full text of the license may be found at
http://opensource.org/licenses/bsd-license.php.
THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
**/
#include "BaseLibInternals.h"
/**
Saves the current CPU context that can be restored with a call to LongJump() and returns 0.
Saves the current CPU context in the buffer specified by JumpBuffer and returns 0. The initial
call to SetJump() must always return 0. Subsequent calls to LongJump() cause a non-zero
value to be returned by SetJump().
If JumpBuffer is NULL, then ASSERT().
For IPF CPUs, if JumpBuffer is not aligned on a 16-byte boundary, then ASSERT().
@param JumpBuffer A pointer to CPU context buffer.
@retval 0 Indicates a return from SetJump().
**/
MdePkg/BaseLib: add attribute 'RETURNS_TWICE' to SetJump When compiling with any ARM toolchain and Os, registers can get trashed when returning for the second time from SetJump because GCC only handles this correctly when using standard names like 'setjmp' or 'getcontext'. When different names are used you have to use the attribute 'returns_twice' to tell gcc to be extra careful. example: extern int FN_NAME(void*); void jmp_buf_set(void *jmpb, void (*f)(void)) { if (!FN_NAME(jmpb)) f(); } this code produces this wrong code with Os: 00000000 <jmp_buf_set>: 0: e92d4010 push {r4, lr} 4: e1a04001 mov r4, r1 8: ebfffffe bl 0 <nonstandard_setjmp> c: e3500000 cmp r0, #0 10: 01a03004 moveq r3, r4 14: 08bd4010 popeq {r4, lr} 18: 012fff13 bxeq r3 1c: e8bd4010 pop {r4, lr} 20: e12fff1e bx lr The generated code pushes backups of r4 and lr to the stack and then saves all registers using nonstandard_setjmp. Then it pops the stack and jumps to the function in r3 which is the main problem because now the function can overwrite our register backups on the stack. When we return a second time from the call to nonstandard_setjmp, the stack pointer has it's original(pushed) position and when the code pops r4 and lr from the stack the values are not guaranteed to be the same. When using a standard name like setjmp or getcontext or adding '__attribute__((returns_twice))' to nonstandard_setjmp's declaration the code looks different: 00000000 <jmp_buf_set>: 0: e92d4007 push {r0, r1, r2, lr} 4: e58d1004 str r1, [sp, #4] 8: ebfffffe bl 0 <setjmp> c: e3500000 cmp r0, #0 10: 059d3004 ldreq r3, [sp, #4] 14: 01a0e00f moveq lr, pc 18: 012fff13 bxeq r3 1c: e28dd00c add sp, sp, #12 20: e49de004 pop {lr} ; (ldr lr, [sp], #4) 24: e12fff1e bx lr Here the problem is being solved by restoring r3 from the stack without popping it. Contributed-under: TianoCore Contribution Agreement 1.1 Signed-off-by: Michael Zimmermann <sigmaepsilon92@gmail.com> Reviewed-by: Liming Gao <liming.gao@intel.com>
2018-01-07 18:31:03 +01:00
RETURNS_TWICE
UINTN
EFIAPI
SetJump (
OUT BASE_LIBRARY_JUMP_BUFFER *JumpBuffer
)
{
InternalAssertJumpBuffer (JumpBuffer);
return 0;
}
/**
Restores the CPU context that was saved with SetJump().
Restores the CPU context from the buffer specified by JumpBuffer.
This function never returns to the caller.
Instead it resumes execution based on the state of JumpBuffer.
@param JumpBuffer A pointer to CPU context buffer.
@param Value The value to return when the SetJump() context is restored.
**/
VOID
EFIAPI
InternalLongJump (
IN BASE_LIBRARY_JUMP_BUFFER *JumpBuffer,
IN UINTN Value
)
{
//
// This function cannot work on EBC
//
ASSERT (FALSE);
}