[L] Change in coreboot[main]: util/cbfstool: Rewrite trampoline in C

[Arthur Heymans (Code Review)]

Attention is currently required from: Elyes Haouas, Paul Menzel.

Hello build bot (Jenkins),

I'd like you to reexamine a change. Please visit

https://review.coreboot.org/c/coreboot/+/63716?usp=email

to look at the new patch set (#6).

Change subject: util/cbfstool: Rewrite trampoline in C
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util/cbfstool: Rewrite trampoline in C

Rewrite the trampoline in C code. Now it does use stack that is set up
at a reasonable offset above the entry point. As a bonus the trampoline
can now check the payload argument instead of searching for "LBIO" in
lower memory.

Works on QEMU q35: tested both with calling argument containing a
pointer to lb_header as with searching lower memory.

Change-Id: Ibbd7a5ecd225edf87f451a82ff4cbe9fea522a89
Signed-off-by: Arthur Heymans 
---
M util/cbfstool/Makefile
D util/cbfstool/linux_trampoline.S
M util/cbfstool/linux_trampoline.c
A util/cbfstool/x86_linux_trampoline.c
4 files changed, 269 insertions(+), 225 deletions(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/16/63716/6