Reviewed-by: Liming Gao <[email protected]> >-----Original Message----- >From: M1cha [mailto:[email protected]] >Sent: Monday, January 08, 2018 1:31 AM >To: [email protected] >Cc: Ard Biesheuvel <[email protected]>; Kinney, Michael D ><[email protected]>; Gao, Liming <[email protected]> >Subject: [edk2] [PATCH v3 2/3] 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 <[email protected]> >--- > 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 05eb4e33a086..39573db0c8da 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 4c0dba55d52f..683527a36fda 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 304f3839b108..652d45d53ba7 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 ( >-- >2.15.1
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