[Bug debug/103975] New: DWARF .debug_frame incorrect for ISRs on AVR; pushing SREG creates off-by-one error

[Bug debug/103975] New: DWARF .debug_frame incorrect for ISRs on AVR; pushing SREG creates off-by-one error

[kimballa at apache dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103975

            Bug ID: 103975
           Summary: DWARF .debug_frame incorrect for ISRs on AVR; pushing
                    SREG creates off-by-one error
           Product: gcc
           Version: 7.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: debug
          Assignee: unassigned at gcc dot gnu.org
          Reporter: kimballa at apache dot org
  Target Milestone: ---

On the AVR platform, when generating ISRs/interrupts/signal handlers (without
using the `naked` attribute), the ISR prologue correctly emits standard code to
read the value of `SREG` from its register port 0x3f and save it to the stack.
However, this is ignored when generating the FDE for stack frame unwind
information in .debug_frame; the result is that for $PC values after that
point, the calculations for the CFA as well as the locations of all
subsequently-pushed registers are off-by-one on the stack. 

The test case (attached) is a minimal ISR:

```
volatile unsigned char x = 0;

ISR(TIMER1_COMPA_vect) {
  x++; // may set carry/overflow flags and affect SREG, forcing it to be
pushed.
}
```

which generates the following (correct) AVR assembly:

```
ISR(TIMER1_COMPA_vect) {
  ce:   1f 92           push    r1
  d0:   0f 92           push    r0
  d2:   0f b6           in      r0, 0x3f        ; 63 # read SREG to r0
  d4:   0f 92           push    r0                   # push SREG on stack
  d6:   11 24           eor     r1, r1
  d8:   8f 93           push    r24
  x++; // may set carry/overflow flags and affect SREG, forcing it to be
pushed.
  da:   80 91 00 01     lds     r24, 0x0100     ; 0x800100 <_edata>
  de:   8f 5f           subi    r24, 0xFF       ; 255
# (ISR continues; remainder elided)
```

A separate bug in binutils/objdump makes `objdump -Wframe` fail to decode the
unwind instructions, but pyelftools can parse the info correctly and shows as
follows:

```
* FDE for __vector_17() starting at $PC=0x00ce:

PC: 00ce {'cfa': CFARule(reg=32, offset=2, expr=None), 36: RegisterRule(OFFSET,
-1)}
PC: 00d0 {'cfa': CFARule(reg=32, offset=3, expr=None), 36: RegisterRule(OFFSET,
-1), 1: RegisterRule(OFFSET, -2)}
PC: 00d2 {'cfa': CFARule(reg=32, offset=4, expr=None), 36: RegisterRule(OFFSET,
-1), 1: RegisterRule(OFFSET, -2), 0: RegisterRule(OFFSET, -3)}

<-- we *should* see a RegisterRule for SREG here valid after $PC=00d4h.

PC: 00da {'cfa': CFARule(reg=32, offset=5, expr=None), 36: RegisterRule(OFFSET,
-1), 1: RegisterRule(OFFSET, -2), 0: RegisterRule(OFFSET, -3), 24:
RegisterRule(OFFSET, -4)}

^-- Even that notwithstanding, the 'push' at 0xd4 means the CFARule offset at
0xda is now 1 too few, and the subsequent RegisterRule offset for r24 makes it
look snug against r0, ignoring the intervening push; CFARule offset should = 6
and r24's rule should have OFFSET=-5.
```

(n.b., gcc refers to $SP as register 32 in the stack frame info, and the return
addr / virtual link register as register 36.)

I am by no means a gcc internals expert but I tried to satisfy myself that it
was a legitimate bug (and not my own goof) by reading the gcc source code. 

I believe the bug is in `gcc/config/avr/avr.c` at lines 1946--47:
```
1946           /* ??? There's no dwarf2 column reserved for SREG.  */
1947           emit_push_sfr (sreg_rtx, false, false /* clr */, AVR_TMP_REGNO);
```

The author's confused comment about lacking an unwind-tracking register for
SREG shows that something might be going wrong here.

I think the 2nd argument to emit_push_sfr() may need to be `true` to set
`frame_related_p=true` (which marks the instruction as
`RTX_FRAME_RELATED_P(insn)=1`). But I don't know what other knock-on effects
frame_related_p=true might have, so it's hard for me to say it's definitely
just a one-flag fix. 

Whether or not unwind info for SREG can be tracked, at minimum the remaining
unwind info needs to account for the extra push to the stack mid-prologue.

I have replicated this with avr-gcc 7.3.0-atmel3.6.1-arduino7 (Arduino's
official package) as well as gcc version 5.4.0 with target=avr, which is what
Ubuntu 20.04.3 installs as `apt install gcc-avr`. Although I couldn't bootstrap
a functioning cross-compiler with gcc 11.2 myself, the source code snippet
above is from the main branch of gcc.git, which makes me believe it's likely
still an issue.

The attached file was created with the 7.3.0 edition of gcc referenced above:
```
$ ./avr-g++ -v
Using built-in specs.
Reading specs from
/home/aaron/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/../lib/gcc/avr/7.3.0/device-specs/specs-avr2
COLLECT_GCC=./avr-g++
COLLECT_LTO_WRAPPER=/home/aaron/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/../libexec/gcc/avr/7.3.0/lto-wrapper
Target: avr
Configured with: ../gcc/configure --enable-fixed-point --enable-languages=c,c++
--prefix=/home/jenkins/workspace/avr-gcc-staging/label/debian7-x86_64/objdir
--disable-nls --disable-libssp --disable-libada --disable-shared
--with-avrlibc=yes --with-dwarf2 --disable-doc --target=avr
Thread model: single
gcc version 7.3.0 (GCC)
```

I'm compiling on Ubuntu 20.04.3 in a VM:
```
$ uname -a
Linux ubuntu 5.4.0-91-generic #102-Ubuntu SMP Fri Nov 5 16:31:28 UTC 2021
x86_64 x86_64 x86_64 GNU/Linux
```

My build target is an Atmel atmega32u4 (`-mmcu=atmega32u4`). 
The command line for my original test-case .c file is:
```
$ avr-gcc -Os -g -Wl,--relax,--gc-section -DARCH_AVR -mmcu=atmega32u4 \
    -DF_CPU=16000000 -fno-exceptions isr.c -o isr.elf
```

If compiled with the avr-gcc 5.4 from Ubuntu, you need to replace `-g` with
`-gdwarf-2` to force it to generate the dwarf sections. 

Thanks
- Aaron

PS Running the above command line with `avr-gcc -v -save-temps -Os -g...` gives
the following log; isr.i is attached:

```
Using built-in specs.
Reading specs from
/home/aaron/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/../lib/gcc/avr/7.3.0/device-specs/specs-atmega32u4
COLLECT_GCC=/home/aaron/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-gcc
COLLECT_LTO_WRAPPER=/home/aaron/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/../libexec/gcc/avr/7.3.0/lto-wrapper
Target: avr
Configured with: ../gcc/configure --enable-fixed-point --enable-languages=c,c++
--prefix=/home/jenkins/workspace/avr-gcc-staging/label/debian7-x86_64/objdir
--disable-nls --disable-libssp --disable-libada --disable-shared
--with-avrlibc=yes --with-dwarf2 --disable-doc --target=avr
Thread model: single
gcc version 7.3.0 (GCC)
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Os' '-g' '-D' 'ARCH_AVR'  '-D'
'F_CPU=16000000' '-fno-exceptions' '-specs=device-specs/specs-atmega32u4'
'-mmcu=avr5'

/home/aaron/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/../libexec/gcc/avr/7.3.0/cc1
-E -quiet -v -imultilib avr5 -iprefix
/home/aaron/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/../lib/gcc/avr/7.3.0/
-D__AVR_ATmega32U4__ -D__AVR_DEVICE_NAME__=atmega32u4 -D ARCH_AVR -D
F_CPU=16000000 isr.c -mn-flash=1 -mno-skip-bug -mmcu=avr5 -fno-exceptions -g
-fworking-directory -Os -fpch-preprocess -o isr.i
ignoring nonexistent directory
"/home/aaron/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/../lib/gcc/avr/7.3.0/../../../../avr/sys-include"
ignoring duplicate directory
"/home/aaron/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/../lib/gcc/../../lib/gcc/avr/7.3.0/include"
ignoring duplicate directory
"/home/aaron/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/../lib/gcc/../../lib/gcc/avr/7.3.0/include-fixed"
ignoring nonexistent directory
"/home/aaron/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/../lib/gcc/../../lib/gcc/avr/7.3.0/../../../../avr/sys-include"
ignoring duplicate directory
"/home/aaron/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/../lib/gcc/../../lib/gcc/avr/7.3.0/../../../../avr/include"
#include "..." search starts here:
#include <...> search starts here:

/home/aaron/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/../lib/gcc/avr/7.3.0/include

/home/aaron/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/../lib/gcc/avr/7.3.0/include-fixed

/home/aaron/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/../lib/gcc/avr/7.3.0/../../../../avr/include
End of search list.
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Os' '-g' '-D' 'ARCH_AVR'  '-D'
'F_CPU=16000000' '-fno-exceptions' '-specs=device-specs/specs-atmega32u4'
'-mmcu=avr5'

/home/aaron/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/../libexec/gcc/avr/7.3.0/cc1
-fpreprocessed isr.i -mn-flash=1 -mno-skip-bug -quiet -dumpbase isr.c
-mmcu=avr5 -auxbase isr -g -Os -version -fno-exceptions -o isr.s
GNU C11 (GCC) version 7.3.0 (avr)
        compiled by GNU C version 4.7.2, GMP version 5.0.2, MPFR version 3.1.0,
MPC version 0.9, isl version none
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
GNU C11 (GCC) version 7.3.0 (avr)
        compiled by GNU C version 4.7.2, GMP version 5.0.2, MPFR version 3.1.0,
MPC version 0.9, isl version none
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: f1a5be5edc2698bbea3030b94defb7b4
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Os' '-g' '-D' 'ARCH_AVR'  '-D'
'F_CPU=16000000' '-fno-exceptions' '-specs=device-specs/specs-atmega32u4'
'-mmcu=avr5'

/home/aaron/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/../lib/gcc/avr/7.3.0/../../../../avr/bin/as
-mmcu=avr5 -mno-skip-bug -o isr.o isr.s
COMPILER_PATH=/home/aaron/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/../libexec/gcc/avr/7.3.0/:/home/aaron/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/../libexec/gcc/:/home/aaron/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/../lib/gcc/avr/7.3.0/../../../../avr/bin/
LIBRARY_PATH=/home/aaron/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/../lib/gcc/avr/7.3.0/avr5/:/home/aaron/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/../lib/gcc/avr/7.3.0/../../../../avr/lib/avr5/:/home/aaron/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/../lib/gcc/avr/7.3.0/:/home/aaron/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/../lib/gcc/:/home/aaron/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/../lib/gcc/avr/7.3.0/../../../../avr/lib/
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Os' '-g' '-D' 'ARCH_AVR'  '-D'
'F_CPU=16000000' '-fno-exceptions' '-specs=device-specs/specs-atmega32u4'
'-mmcu=avr5'

/home/aaron/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/../libexec/gcc/avr/7.3.0/collect2
-plugin
/home/aaron/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/../libexec/gcc/avr/7.3.0/liblto_plugin.so
-plugin-opt=/home/aaron/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/../libexec/gcc/avr/7.3.0/lto-wrapper
-plugin-opt=-fresolution=isr.res -plugin-opt=-pass-through=-lgcc
-plugin-opt=-pass-through=-lm -plugin-opt=-pass-through=-lc
-plugin-opt=-pass-through=-latmega32u4 -mavr5 -Tdata 0x800100
/home/aaron/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/../lib/gcc/avr/7.3.0/../../../../avr/lib/avr5/crtatmega32u4.o
-L/home/aaron/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/../lib/gcc/avr/7.3.0/avr5
-L/home/aaron/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/../lib/gcc/avr/7.3.0/../../../../avr/lib/avr5
-L/home/aaron/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/../lib/gcc/avr/7.3.0
-L/home/aaron/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/../lib/gcc
-L/home/aaron/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/../lib/gcc/avr/7.3.0/../../../../avr/lib
--relax --gc-section isr.o --start-group -lgcc -lm -lc -latmega32u4 --end-group
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Os' '-g' '-D' 'ARCH_AVR'  '-D'
'F_CPU=16000000' '-fno-exceptions' '-specs=device-specs/specs-atmega32u4'
'-mmcu=avr5'
```

[Bug debug/103975] DWARF .debug_frame incorrect for ISRs on AVR; pushing SREG creates off-by-one error

[kimballa at apache dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103975

--- Comment #1 from Aaron Kimball <kimballa at apache dot org> ---
Created attachment 52160
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=52160&action=edit
isr.i that generates incorrect .debug_frame info

Attaching isr.i test case file

[Bug debug/103975] DWARF .debug_frame incorrect for ISRs on AVR; pushing SREG creates off-by-one error

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103975

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |wrong-debug

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Can you try a newer verison of GCC since 7.x is no longer support like maybe
11.2.0 or even 10.3.0?

[Bug target/103975] DWARF .debug_frame incorrect for ISRs on AVR; pushing SREG creates off-by-one error

[kimballa at apache dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103975

--- Comment #3 from Aaron Kimball <kimballa at apache dot org> ---
(In reply to Andrew Pinski from comment #2)
> Can you try a newer verison of GCC since 7.x is no longer support like maybe
> 11.2.0 or even 10.3.0?

Hi Andrew,

I tried again and figured out the issue in my `PATH` that was preventing my
cross-compiler from working correctly. I now have gcc 11.2.0, binutils 2.37,
and avr-gcc 2.0.0 built from source, working together.

The issue remains. (Actually, if anything it's worse.)

I had to modify the test case as the original very-simple test now succeeds by
virtue of gcc being smarter about eliminating unnecessary register saves. The
issue can still be reproduced by increasing register pressure in the ISR. I
defined a larger number of `volatile unsigned char` global variables and added
them together with:

```
ISR(TIMER1_COMPA_vect) {
  x++;
  x += a + b + c + d + e + f + g + h + i + j + k + m + n + p;
}
```

This yields the following disassembly:
```
ISR(TIMER1_COMPA_vect) {
  ce:   1f 92           push    r1
  d0:   1f b6           in      r1, 0x3f        ; 63  # read SREG port
  d2:   1f 92           push    r1                    # push SREG
  d4:   11 24           eor     r1, r1
  d6:   1f 93           push    r17
  d8:   2f 93           push    r18
  da:   3f 93           push    r19
  dc:   4f 93           push    r20
# ... prologue continues ... (snip)
  f2:   ff 93           push    r31   # last line of prologue
# remainder of disasm snipped
```

As a bonus w/ this toolchain, binutils 2.37 has fixed the bug in objdump that
prevented it from reading .debug_frame entries correctly. 

Thus, `avr-objdump -Wframe ~/isr.elf` shows the following:
```
00000000 0010 ffffffff CIE
  Version:               1
  Augmentation:          ""
  Code alignment factor: 2
  Data alignment factor: -1
  Return address column: 36

  DW_CFA_def_cfa: r32 ofs 2
  DW_CFA_offset: r36 at cfa-1
  DW_CFA_nop
  DW_CFA_nop

00000014 0054 00000000 FDE cie=00000000 pc=00ce..00ce
  DW_CFA_restore: r14
  DW_CFA_nop
  DW_CFA_nop
  DW_CFA_nop
                                 # ... no records for $PC=0xd0, 0xd4, 0xd8 ?
  DW_CFA_advance_loc: 12 to 00da
  DW_CFA_def_cfa_offset: 3
  DW_CFA_offset: r18 at cfa-2    # <-- r18 marked as 1'st reg saved. 
                                 # (cfa-0 & cfa-1 implicitly consumed by r36/PC
                                 # per the CIE)
                                 # ... but what happened to r1, SREG, and r17?
                                 # even if ABI says r1/r17 are disposable (??),
                                 # r18 should be at CFA-5 based on the pushes.
  DW_CFA_advance_loc: 2 to 00dc
  DW_CFA_def_cfa_offset: 4
  DW_CFA_offset: r19 at cfa-3
  DW_CFA_advance_loc: 2 to 00de
  DW_CFA_def_cfa_offset: 5
  DW_CFA_offset: r20 at cfa-4
# ... remainder snipped...
```

At 0xf4 (after prologue is complete) the FDE should have CFA at offset r32 +
19. However, it's missing 3 bytes and has:

```
  DW_CFA_advance_loc: 2 to 00f4
  DW_CFA_def_cfa_offset: 16   # Should be 19: 2 for return pc + 17 push ops
  DW_CFA_offset: r31 at cfa-15
```


Compilation command was:
```
$ avr/bin/avr-gcc  -Os -g  -Wl,--relax,--gc-section -DARCH_AVR \
  -mmcu=atmega32u4 -DF_CPU=16000000 -fno-exceptions ~/isr.c -o ~/isr.elf
```

Compiler build configuration is:
```
aaron@ubuntu:~/share/scratch/gcc11avr$ avr/bin/avr-gcc -v
Using built-in specs.
Reading specs from
/home/aaron/share/scratch/gcc11avr/avr/lib/gcc/avr/11.2.0/device-specs/specs-avr2
COLLECT_GCC=avr/bin/avr-gcc
COLLECT_LTO_WRAPPER=/home/aaron/share/scratch/gcc11avr/avr/libexec/gcc/avr/11.2.0/lto-wrapper
Target: avr
Configured with: ../gcc-11.2.0/configure
--prefix=/home/aaron/share/scratch/gcc11avr
--exec-prefix=/home/aaron/share/scratch/gcc11avr/avr
--with-local-prefix=/home/aaron/share/scratch/gcc11avr/local
--enable-fixed-point --enable-languages=c,c++ --disable-nls --disable-libssp
--disable-libada --disable-shared --disable-threads --with-avrlibc
--with-dwarf2 --disable-doc --target=avr
--with-toolexeclibdir=/home/aaron/share/scratch/gcc11avr/avr/lib
--with-sysroot=/home/aaron/share/scratch/gcc11avr/avr --with-avrlibc
--with-double=32
Thread model: single
Supported LTO compression algorithms: zlib
gcc version 11.2.0 (GCC)
```

Log when building with `-v -save-temps` is:
```
aaron@ubuntu:~/share/scratch/gcc11avr$ avr/bin/avr-gcc -v -save-temps  -Os -g 
-Wl,--relax,--gc-section -DARCH_AVR -mmcu=atmega32u4 -DF_CPU=16000000 
-fno-exceptions ~/isr.c -o ~/isr.elf
Using built-in specs.
Reading specs from
/home/aaron/share/scratch/gcc11avr/avr/lib/gcc/avr/11.2.0/device-specs/specs-atmega32u4
COLLECT_GCC=avr/bin/avr-gcc
COLLECT_LTO_WRAPPER=/home/aaron/share/scratch/gcc11avr/avr/libexec/gcc/avr/11.2.0/lto-wrapper
Target: avr
Configured with: ../gcc-11.2.0/configure
--prefix=/home/aaron/share/scratch/gcc11avr
--exec-prefix=/home/aaron/share/scratch/gcc11avr/avr
--with-local-prefix=/home/aaron/share/scratch/gcc11avr/local
--enable-fixed-point --enable-languages=c,c++ --disable-nls --disable-libssp
--disable-libada --disable-shared --disable-threads --with-avrlibc
--with-dwarf2 --disable-doc --target=avr
--with-toolexeclibdir=/home/aaron/share/scratch/gcc11avr/avr/lib
--with-sysroot=/home/aaron/share/scratch/gcc11avr/avr --with-avrlibc
--with-double=32
Thread model: single
Supported LTO compression algorithms: zlib
gcc version 11.2.0 (GCC)
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Os' '-g' '-D' 'ARCH_AVR'  '-D'
'F_CPU=16000000' '-fno-exceptions' '-o' '/home/aaron/isr.elf' '-mdouble=32'
'-mlong-double=64' '-specs=device-specs/specs-atmega32u4' '-mmcu=avr5'
'-dumpdir' '/home/aaron/isr.elf-'
 /home/aaron/share/scratch/gcc11avr/avr/libexec/gcc/avr/11.2.0/cc1 -E -quiet -v
-imultilib avr5 -D__AVR_ATmega32U4__ -D__AVR_DEVICE_NAME__=atmega32u4 -D
ARCH_AVR -D F_CPU=16000000 /home/aaron/isr.c -mn-flash=1 -mno-skip-bug
-mdouble=32 -mlong-double=64 -mmcu=avr5 -fno-exceptions -g -fworking-directory
-Os -fpch-preprocess -o /home/aaron/isr.elf-isr.i
ignoring nonexistent directory
"/home/aaron/share/scratch/gcc11avr/avr/home/aaron/share/scratch/gcc11avr/local/include"
#include "..." search starts here:
#include <...> search starts here:
 /home/aaron/share/scratch/gcc11avr/avr/lib/gcc/avr/11.2.0/include
 /home/aaron/share/scratch/gcc11avr/avr/lib/gcc/avr/11.2.0/include-fixed

/home/aaron/share/scratch/gcc11avr/avr/lib/gcc/avr/11.2.0/../../../../../avr/include
 /home/aaron/share/scratch/gcc11avr/avr/usr/include
End of search list.
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Os' '-g' '-D' 'ARCH_AVR'  '-D'
'F_CPU=16000000' '-fno-exceptions' '-o' '/home/aaron/isr.elf' '-mdouble=32'
'-mlong-double=64' '-specs=device-specs/specs-atmega32u4' '-mmcu=avr5'
'-dumpdir' '/home/aaron/isr.elf-'
 /home/aaron/share/scratch/gcc11avr/avr/libexec/gcc/avr/11.2.0/cc1
-fpreprocessed /home/aaron/isr.elf-isr.i -mn-flash=1 -mno-skip-bug -quiet
-dumpdir /home/aaron/isr.elf- -dumpbase isr.c -dumpbase-ext .c -mdouble=32
-mlong-double=64 -mmcu=avr5 -g -Os -version -fno-exceptions -o
/home/aaron/isr.elf-isr.s
GNU C17 (GCC) version 11.2.0 (avr)
        compiled by GNU C version 9.3.0, GMP version 6.1.0, MPFR version 3.1.6,
MPC version 1.0.3, isl version isl-0.18-GMP

GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
GNU C17 (GCC) version 11.2.0 (avr)
        compiled by GNU C version 9.3.0, GMP version 6.1.0, MPFR version 3.1.6,
MPC version 1.0.3, isl version isl-0.18-GMP

GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: 70441dcee53d290afd2c7af2e72d480e
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Os' '-g' '-D' 'ARCH_AVR'  '-D'
'F_CPU=16000000' '-fno-exceptions' '-o' '/home/aaron/isr.elf' '-mdouble=32'
'-mlong-double=64' '-specs=device-specs/specs-atmega32u4' '-mmcu=avr5'
'-dumpdir' '/home/aaron/isr.elf-'
 as --gdwarf-5 -mmcu=avr5 -mgcc-isr -mno-skip-bug -o /home/aaron/isr.elf-isr.o
/home/aaron/isr.elf-isr.s
COMPILER_PATH=/home/aaron/share/scratch/gcc11avr/avr/libexec/gcc/avr/11.2.0/:/home/aaron/share/scratch/gcc11avr/avr/libexec/gcc/avr/11.2.0/:/home/aaron/share/scratch/gcc11avr/avr/libexec/gcc/avr/:/home/aaron/share/scratch/gcc11avr/avr/lib/gcc/avr/11.2.0/:/home/aaron/share/scratch/gcc11avr/avr/lib/gcc/avr/
LIBRARY_PATH=/home/aaron/share/scratch/gcc11avr/avr/lib/gcc/avr/11.2.0/avr5/:/home/aaron/share/scratch/gcc11avr/avr/lib/avr5/:/home/aaron/share/scratch/gcc11avr/avr/lib/gcc/avr/11.2.0/:/home/aaron/share/scratch/gcc11avr/avr/lib/
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Os' '-g' '-D' 'ARCH_AVR'  '-D'
'F_CPU=16000000' '-fno-exceptions' '-o' '/home/aaron/isr.elf' '-mdouble=32'
'-mlong-double=64' '-specs=device-specs/specs-atmega32u4' '-mmcu=avr5'
'-dumpdir' '/home/aaron/isr.elf.'
 /home/aaron/share/scratch/gcc11avr/avr/libexec/gcc/avr/11.2.0/collect2 -plugin
/home/aaron/share/scratch/gcc11avr/avr/libexec/gcc/avr/11.2.0/liblto_plugin.so
-plugin-opt=/home/aaron/share/scratch/gcc11avr/avr/libexec/gcc/avr/11.2.0/lto-wrapper
-plugin-opt=-fresolution=/home/aaron/isr.elf.res
-plugin-opt=-pass-through=-lgcc -plugin-opt=-pass-through=-lm
-plugin-opt=-pass-through=-lc -plugin-opt=-pass-through=-latmega32u4
--sysroot=/home/aaron/share/scratch/gcc11avr/avr -mavr5 -Tdata 0x800100 -o
/home/aaron/isr.elf
/home/aaron/share/scratch/gcc11avr/avr/lib/avr5/crtatmega32u4.o
-L/home/aaron/share/scratch/gcc11avr/avr/lib/gcc/avr/11.2.0/avr5
-L/home/aaron/share/scratch/gcc11avr/avr/lib/avr5
-L/home/aaron/share/scratch/gcc11avr/avr/lib/gcc/avr/11.2.0
-L/home/aaron/share/scratch/gcc11avr/avr/lib --relax --gc-section
/home/aaron/isr.elf-isr.o --start-group -lgcc -lm -lc -latmega32u4 --end-group
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Os' '-g' '-D' 'ARCH_AVR'  '-D'
'F_CPU=16000000' '-fno-exceptions' '-o' '/home/aaron/isr.elf' '-mdouble=32'
'-mlong-double=64' '-specs=device-specs/specs-atmega32u4' '-mmcu=avr5'
'-dumpdir' '/home/aaron/isr.elf.'
```

[Bug target/103975] DWARF .debug_frame incorrect for ISRs on AVR; pushing SREG creates off-by-one error

[kimballa at apache dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103975

--- Comment #4 from Aaron Kimball <kimballa at apache dot org> ---
Created attachment 52161
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=52161&action=edit
Test case for gcc 11.2.0 demonstrating issue

Attaching updated test case for gcc 11.2.0

[Bug target/103975] DWARF .debug_frame incorrect for ISRs on AVR; pushing SREG creates off-by-one error

[gjl at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103975

--- Comment #5 from Georg-Johann Lay <gjl at gcc dot gnu.org> ---
If someone is going to fix this, the following changes might also play a role:

* v8+ may emit optimized ISR prologues / epilogues using PR81268: gcc will just
emit pseudo-instruction __gcc_isr which will be resolved by gas.  Debug info
might be incorrect or missing; gas would have to add respective debug info.

* v12+ PR92729 changed condition code from implicit cc0 to explicit REG_CC and
introduced a new hard register "cc" with hard register number REG_CC = 36. The
highest hard regno before that transition was 35.