[Bug c/107756] New: Change in sizeof(enum) with -std=gnu11 breaks Linux kernel code compilation (PR c/36113 change regression)

[Bug c/107756] New: Change in sizeof(enum) with -std=gnu11 breaks Linux kernel code compilation (PR c/36113 change regression)

[macro at orcam dot me.uk]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107756

            Bug ID: 107756
           Summary: Change in sizeof(enum) with -std=gnu11 breaks Linux
                    kernel code compilation (PR c/36113 change regression)
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: macro at orcam dot me.uk
                CC: jsm28 at gcc dot gnu.org
  Target Milestone: ---
            Target: mips-linux-gnu

Created attachment 53929
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=53929&action=edit
Preprocessor output from libahci.c; use lzip to decompress

The fix for PR c/36113 has added support for C2x enums wider than int,
but it seems to affect code built for earlier standards, such as with
`-std=gnu11' and libahci.c code from Linux kernel, which causes an
assertion failure with the `mips-linux-gnu' (o32) target as from commit
3b3083a598ca ("c: C2x enums wider than int [PR36113]"):

In file included from <command-line>:
drivers/ata/libahci.c: In function 'ahci_led_store':
././include/linux/compiler_types.h:357:45: error: call to
'__compiletime_assert_309' declared with attribute error: BUILD_BUG_ON failed:
sizeof(_s) > sizeof(long)
  357 |         _compiletime_assert(condition, msg, __compiletime_assert_,
__COUNTER__)
      |                                             ^
././include/linux/compiler_types.h:338:25: note: in definition of macro
'__compiletime_assert'
  338 |                         prefix ## suffix();                            
\
      |                         ^~~~~~
././include/linux/compiler_types.h:357:9: note: in expansion of macro
'_compiletime_assert'
  357 |         _compiletime_assert(condition, msg, __compiletime_assert_,
__COUNTER__)
      |         ^~~~~~~~~~~~~~~~~~~
./include/linux/build_bug.h:39:37: note: in expansion of macro
'compiletime_assert'
   39 | #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
      |                                     ^~~~~~~~~~~~~~~~~~
./include/linux/build_bug.h:50:9: note: in expansion of macro
'BUILD_BUG_ON_MSG'
   50 |         BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
      |         ^~~~~~~~~~~~~~~~
./include/linux/nospec.h:58:9: note: in expansion of macro 'BUILD_BUG_ON'
   58 |         BUILD_BUG_ON(sizeof(_s) > sizeof(long));                       
\
      |         ^~~~~~~~~~~~
drivers/ata/libahci.c:1198:23: note: in expansion of macro 'array_index_nospec'
 1198 |                 pmp = array_index_nospec(pmp, EM_MAX_SLOTS);
      |                       ^~~~~~~~~~~~~~~~~~

with the compiler invocation as follows:

mips-linux-gnu-gcc -Wp,-MMD,drivers/ata/.libahci.o.d  -nostdinc
-I./arch/mips/include -I./arch/mips/include/generated  -I./include
-I./arch/mips/include/uapi -I./arch/mips/include/generated/uapi
-I./include/uapi -I./include/generated/uapi -include
./include/linux/compiler-version.h -include ./include/linux/kconfig.h -include
./include/linux/compiler_types.h -D__KERNEL__
-DVMLINUX_LOAD_ADDRESS=0xffffffff80100000 -DLINKER_LOAD_ADDRESS=0x80100000
-DDATAOFFSET=0 -fmacro-prefix-map=./= -Wall -Wundef -Werror=strict-prototypes
-Wno-trigraphs -fno-strict-aliasing -fno-common -fshort-wchar -fno-PIE
-Werror=implicit-function-declaration -Werror=implicit-int -Werror=return-type
-Wno-format-security -std=gnu11 -mno-check-zero-division -mabi=32 -G 0
-mno-abicalls -fno-pic -pipe -msoft-float -DGAS_HAS_SET_HARDFLOAT
-Wa,-msoft-float -ffreestanding -EB -fno-stack-check
-Wa,-mno-fix-loongson3-llsc -march=mips32r2 -Wa,--trap
-DTOOLCHAIN_SUPPORTS_VIRT -DTOOLCHAIN_SUPPORTS_XPA -DTOOLCHAIN_SUPPORTS_CRC
-DTOOLCHAIN_SUPPORTS_DSP -DTOOLCHAIN_SUPPORTS_GINV
-I./arch/mips/include/asm/mach-malta -I./arch/mips/include/asm/mach-generic
-fno-asynchronous-unwind-tables -fno-delete-null-pointer-checks
-Wno-frame-address -Wno-format-truncation -Wno-format-overflow
-Wno-address-of-packed-member -O2 -fno-allow-store-data-races
-Wframe-larger-than=2048 -fno-stack-protector -Wno-main
-Wno-unused-but-set-variable -Wno-unused-const-variable -Wno-dangling-pointer
-fomit-frame-pointer -fno-stack-clash-protection -Wdeclaration-after-statement
-Wvla -Wno-pointer-sign -Wcast-function-type -Wno-stringop-truncation
-Wno-stringop-overflow -Wno-restrict -Wno-maybe-uninitialized
-Wno-alloc-size-larger-than -Wimplicit-fallthrough=5 -fno-strict-overflow
-fno-stack-check -fconserve-stack -Werror=date-time
-Werror=incompatible-pointer-types -Werror=designated-init
-Wno-packed-not-aligned    -DKBUILD_MODFILE='"drivers/ata/libahci"'
-DKBUILD_BASENAME='"libahci"' -DKBUILD_MODNAME='"libahci"'
-D__KBUILD_MODNAME=kmod_libahci -c -o drivers/ata/libahci.o
drivers/ata/libahci.c

This code builds just fine with earlier GCC checkouts.

I have attached preprocessor output from libahci.c.

[Bug c/107756] Change in sizeof(enum) with -std=gnu11 breaks Linux kernel code compilation (PR c/36113 change regression)

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107756

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |DUPLICATE
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
In older C standard versions such enums are invalid.

*** This bug has been marked as a duplicate of bug 107405 ***