From 2117989c262d132ace1da033046883a9086f6eac Mon Sep 17 00:00:00 2001 From: M1cha Date: Mon, 8 Jan 2018 01:31:03 +0800 Subject: [PATCH] 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 : 0: e92d4010 push {r4, lr} 4: e1a04001 mov r4, r1 8: ebfffffe bl 0 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 : 0: e92d4007 push {r0, r1, r2, lr} 4: e58d1004 str r1, [sp, #4] 8: ebfffffe bl 0 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 Reviewed-by: Liming Gao --- MdePkg/Include/Library/BaseLib.h | 1 + MdePkg/Library/BaseLib/Ebc/SetJumpLongJump.c | 1 + MdePkg/Library/BaseLib/Ia32/SetJump.c | 1 + 3 files changed, 3 insertions(+) diff --git a/MdePkg/Include/Library/BaseLib.h b/MdePkg/Include/Library/BaseLib.h index 05eb4e33a0..39573db0c8 100644 --- a/MdePkg/Include/Library/BaseLib.h +++ b/MdePkg/Include/Library/BaseLib.h @@ -4903,6 +4903,7 @@ MemoryFence ( @retval 0 Indicates a return from SetJump(). **/ +RETURNS_TWICE UINTN EFIAPI SetJump ( diff --git a/MdePkg/Library/BaseLib/Ebc/SetJumpLongJump.c b/MdePkg/Library/BaseLib/Ebc/SetJumpLongJump.c index 4c0dba55d5..683527a36f 100644 --- a/MdePkg/Library/BaseLib/Ebc/SetJumpLongJump.c +++ b/MdePkg/Library/BaseLib/Ebc/SetJumpLongJump.c @@ -32,6 +32,7 @@ @retval 0 Indicates a return from SetJump(). **/ +RETURNS_TWICE UINTN EFIAPI SetJump ( diff --git a/MdePkg/Library/BaseLib/Ia32/SetJump.c b/MdePkg/Library/BaseLib/Ia32/SetJump.c index 304f3839b1..652d45d53b 100644 --- a/MdePkg/Library/BaseLib/Ia32/SetJump.c +++ b/MdePkg/Library/BaseLib/Ia32/SetJump.c @@ -49,6 +49,7 @@ InternalAssertJumpBuffer ( **/ _declspec (naked) +RETURNS_TWICE UINTN EFIAPI SetJump ( -- 2.39.2