https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83994
Bug ID: 83994
Summary: %ebx is clobbered by stack-clash probing for regparm-3
function in PIC mode
Product: gcc
Version: 8.0
Status: UNCONFIRMED
Keywords: wrong-code
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: fw at gcc dot gnu.org
Target Milestone: ---
Target: i686
Created attachment 43219
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=43219&action=edit
regparm-3-pic-probe.c
The attached reproducer, when compiled with -O2 -m32 -march=i686 -fpic
-fstack-clash-protection, clobbers %ebx in PIC mode due to the probing at the
start of the function. (Seen on trunk@25693.)
The comment on get_scratch_register_on_entry says:
/* Return a short-lived scratch register for use on function entry.
In 32-bit mode, it is valid only after the registers are saved
in the prologue. This register must be released by means of
release_scratch_register_on_entry once it is dead. */
This is called from ix86_adjust_stack_and_probe_stack_clash, but in the
reproducer, this happens when int_registers_saved is still false in
ix86_expand_prologue. It seems that in this case, ix86_save_reg cannot be used
to select a register which is save to clobber.
