[Bug libgcc/104988] New: Zero register (R1) clobbered by __udivmodsi4 for AVR

[Bug libgcc/104988] New: Zero register (R1) clobbered by __udivmodsi4 for AVR

[dv at vollmann dot ch]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104988

            Bug ID: 104988
           Summary: Zero register (R1) clobbered by __udivmodsi4 for AVR
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libgcc
          Assignee: unassigned at gcc dot gnu.org
          Reporter: dv at vollmann dot ch
                CC: dv at vollmann dot ch
  Target Milestone: ---

Created attachment 52652
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=52652&action=edit
compiler configuration

Line 1630 in libgcc/config/avr/lib1funcs.S defined r_cnt as __zero_reg__ and
uses it as loop count, i.e. it sets it to a non-zero value.
This is fine if the loop reaches its end, but causes chaos if there's an
interrupt before the loop end.
__zero_reg__ should never be set to a non-zero value!
Looking through the file there seem to be a number of other places where
__zero_reg__ is modified.

[Bug target/104988] Zero register (R1) clobbered by __udivmodsi4 for AVR

[dv at vollmann dot ch]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104988

--- Comment #1 from dv at vollmann dot ch ---
Sorry, it looks like it's my fault: the compiler saves and clears __zero_reg__
for ISRs so I have to do this in my assembler ISRs myself and it's correct for
a function to temporarily store a non-zero value in __zero_reg__.

Sorry for the noise.

[Bug target/104988] Zero register (R1) clobbered by __udivmodsi4 for AVR

[gjl at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104988

Georg-Johann Lay <gjl at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |INVALID
             Status|UNCONFIRMED                 |RESOLVED

--- Comment #2 from Georg-Johann Lay <gjl at gcc dot gnu.org> ---
As you already found out this PR is invalid, thus closing.