Bug in grub_xputs_normal

[Stephan Gabert]

Hello dear GRUB developers,

I recently came across a strange behavior of GRUB2:

Calling grub_printf with an 80 character string (grub_printf(str) == 80) 
80 times in a row leads to grub being unresponsive and de facto being 
trapped in endless loop (of printing newlines?).

This behavior does not occur before switching to normal mode, when 
grub_printf still calls grub_xputs_dumb. It only occurs after switching 
to normal mode, when grub_printf calls grub_xputs_normal.

The bug is not triggered, if 80*80 (or more) characters are being 
printed at once by grub_printf:
A string of at least 80 characters has to be grub_printf'd at least 80 
times in a row.

I attached a small patch to demonstrate the bug:
- printf_test prints an 80-char long string 80 times successively
- this test succeeds with grub_printf using grub_xputs_dumb (before 
normal mode)
- this test fails with grub_printf using grub_xputs_normal (after 
switching to normal mode)

I could reproduce this behavior within qemu and on several different 
physical systems. For testing, I used the current master-branch and 
grub-2.02-rc2 (8014b7b), but prior versions are affected too probably.

Best regards,
Stephan

bug-xputs.patch
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