InternalX86EnablePaging64() does a call to the new 64-bit entry point. This
call breaks our debugger stack walking code. We need it to be a push $0/jmp. In
place of a call. The push $0/jmp makes the return address from the call be 0,
and this tells the debugger to stop walking the frame. In clang and some
flavors of GCC all C functions spill enough state to the stack so that you can
walk the stack via an algorithm (on VC++ for X64 you need symbols).
If this change is OK with folks I can submit a patch.
https://svn.code.sf.net/p/edk2/code/trunk/edk2/MdePkg/Library/BaseLib/X64/SwitchStack.S
#
# Reserve space for register parameters (rcx, rdx, r8 & r9) on the stack,
# in case the callee wishes to spill them.
#
lea -0x20(%r9), %rsp
pushq $0 // stop gdb stack unwind
jmp *%rax // call EntryPoint ()
https://svn.code.sf.net/p/edk2/code/trunk/edk2/MdePkg/Library/BaseLib/Ia32/EnablePaging64.S
.byte 0x48
addl $0x-0x20, %esp # add rsp, -20h
call *%ebx # call rbx
jmp . # no one should get here
So what we would like to see is:
.byte 0x48
addl $0x-0x20, %esp # add rsp, -20h
push $0 // stop gdb stack unwind
jmp *%ebx // call EntryPoint ()
Thanks,
Andrew Fish
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