[Bug c/97448] New: Unneccessary stack frame when using stack protector

[Bug c/97448] New: Unneccessary stack frame when using stack protector

[christophe.leroy at csgroup dot eu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97448

            Bug ID: 97448
           Summary: Unneccessary stack frame when using stack protector
           Product: gcc
           Version: 10.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: christophe.leroy at csgroup dot eu
  Target Milestone: ---

While building Linux kernel for 32 bits powerpc with GCC 10.1 with stack frame
protection, functions that don't use the stack at all get a pointless stack
frame, while they don't when stackframe protection is not used:

c0016af4 <get_order>:
c0016af4:       38 63 ff ff     addi    r3,r3,-1
c0016af8:       94 21 ff f0     stwu    r1,-16(r1)
c0016afc:       54 63 a3 3e     rlwinm  r3,r3,20,12,31
c0016b00:       7c 63 00 34     cntlzw  r3,r3
c0016b04:       20 63 00 20     subfic  r3,r3,32
c0016b08:       38 21 00 10     addi    r1,r1,16
c0016b0c:       4e 80 00 20     blr



c000d1b8 <raw_copy_from_user>:
c000d1b8:       94 21 ff f0     stwu    r1,-16(r1)
c000d1bc:       38 21 00 10     addi    r1,r1,16
c000d1c0:       48 00 c5 44     b       c0019704 <__copy_tofrom_user>


Used GCC version:

GCC version with the BUG:

Using built-in specs.
COLLECT_GCC=/opt/gcc-10.1.0-nolibc/powerpc64-linux/bin/powerpc64-linux-gcc
COLLECT_LTO_WRAPPER=/home/opt/gcc-10.1.0-nolibc/powerpc64-linux/bin/../libexec/gcc/powerpc64-linux/10.1.0/lto-wrapper
Target: powerpc64-linux
Configured with: /home/arnd/git/gcc/configure --target=powerpc64-linux
--enable-targets=all
--prefix=/home/arnd/cross/x86_64/gcc-10.1.0-nolibc/powerpc64-linux
--enable-languages=c --without-headers --disable-bootstrap --disable-nls
--disable-threads --disable-shared --disable-libmudflap --disable-libssp
--disable-libgomp --disable-decimal-float --disable-libquadmath
--disable-libatomic --disable-libcc1 --disable-libmpx --enable-checking=release
Thread model: single
Supported LTO compression algorithms: zlib
gcc version 10.1.0 (GCC)


Build command:

powerpc64-linux-gcc -Wp,-MMD,arch/powerpc/kernel/.setup-common.o.d  -nostdinc
-isystem
/home/opt/gcc-10.1.0-nolibc/powerpc64-linux/bin/../lib/gcc/powerpc64-linux/10.1.0/include
-I./arch/powerpc/include -I./arch/powerpc/include/generated  -I./include
-I./arch/powerpc/include/uapi -I./arch/powerpc/include/generated/uapi
-I./include/uapi -I./include/generated/uapi -include ./include/linux/kconfig.h
-include ./include/linux/compiler_types.h -D__KERNEL__ -I ./arch/powerpc -Wall
-Wundef -Werror=strict-prototypes -Wno-trigraphs -fno-strict-aliasing
-fno-common -fshort-wchar -fno-PIE -Werror=implicit-function-declaration
-Werror=implicit-int -Wno-format-security -std=gnu89 -mcpu=powerpc
-mcpu=powerpc -m32 -msoft-float -pipe -ffixed-r2 -mmultiple
-mno-readonly-in-sdata -mcpu=powerpc64 -mno-altivec -mno-vsx
-fno-asynchronous-unwind-tables -mno-string -mbig-endian
-mstack-protector-guard=tls -mstack-protector-guard-reg=r2
-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=1024 -fstack-protector
-Wno-unused-but-set-variable -Wimplicit-fallthrough -Wno-unused-const-variable
-fomit-frame-pointer -fno-var-tracking-assignments
-Wdeclaration-after-statement -Wvla -Wno-pointer-sign -Wno-stringop-truncation
-Wno-zero-length-bounds -Wno-array-bounds -Wno-stringop-overflow -Wno-restrict
-Wno-maybe-uninitialized -fno-strict-overflow -fno-merge-all-constants
-fmerge-constants -fno-stack-check -fconserve-stack -Werror=date-time
-Werror=incompatible-pointer-types -Werror=designated-init
-fmacro-prefix-map=./= -Wno-packed-not-aligned
-mstack-protector-guard-offset=552 -Werror   
-DKBUILD_MODFILE='"arch/powerpc/kernel/setup-common"'
-DKBUILD_BASENAME='"setup_common"' -DKBUILD_MODNAME='"setup_common"' -c -o
arch/powerpc/kernel/setup-common.o arch/powerpc/kernel/setup-common.c

[Bug target/97448] Unneccessary stack frame when using stack protector

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97448

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Target|powerpc                     |powerpc-*-*linux (32bit)

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Reduced testcase -O2 -fstack-protector:
int fls64(int x)
{
        return x;
}