Compiling gcc fails while trying to link libgcc

Compiling gcc fails while trying to link libgcc

[Peter Lamby]

Hello everyone,

this is a crosspost from Stackoverflow[1].

I am trying to compile gccc 10.1.0 for linux. I am cross compiling since
I don't have an existing gcc.

Im using musl as libc.

My CFLAGS are:
```
export CFLAGS=-pipe -march=native -fstack-protector-strong -fno-plt \
-pie -fpie
```

I started by installing binutils:
```
../binutils-2.34/configure
--target=x86_64-unknown-linux-musl --host=x86_64-unknown-linux-musl \
--build=x86_64-pc-linux-gnu --enable-lto --prefix=/usr --disable-nls \
--disable-multilib
make -j5 MAKEINFO=true
make -j5 MAKEINFO=true DESTDIR=$SOS_HOME install
```

Which seemed to work. I can run the created executables when I boot into
the system.

I then tried to install gcc:
```
../gcc-10.1.0/configure
--target=x86_64-unknown-linux-musl --host=x86_64-unknown-linux-musl \
--build=x86_64-pc-linux-gnu --enable-lto --prefix=/usr --disable-nls \
--disable-multilib --enable-languages=c --without-isl --with-newlib \
--disable-libsanitizer --with-sysroot=/root/mnt
make
```

(I changed the configure script a little bit so that the intel CET
detection worked while crosscompiling.)

After while make tries to execute:
```
x86_64-unknown-linux-musl-gcc   -O2  -g -O2 -pipe -march=native
-fstack-protector-strong -fno-plt -pie -fpie -DIN_GCC    -W -Wall
-Wno-narrowing -Wwrite-strings -Wcast-qual -Wstrict-prototypes
-Wmissing-prototypes -Wold-style-definition  -isystem ./include   -fpic
-mlong-double-80 -DUSE_ELF_SYMVER  -DGTHREAD_USE_WEAK=0 -g -DIN_LIBGCC2
-fbuilding-libgcc -fno-stack-protector -Dinhibit_libc -shared
-nodefaultlibs -Wl,--soname=libgcc_s.so.1
-Wl,--version-script=libgcc.map -o ./libgcc_s.so.1.tmp -g -O2 -pipe
-march=native -fstack-protector-strong -fno-plt -pie -fpie -B./
_muldi3_s.o _negdi2_s.o _lshrdi3_s.o _ashldi3_s.o _ashrdi3_s.o
_cmpdi2_s.o _ucmpdi2_s.o _clear_cache_s.o _trampoline_s.o __main_s.o
_absvsi2_s.o _absvdi2_s.o _addvsi3_s.o _addvdi3_s.o _subvsi3_s.o
_subvdi3_s.o _mulvsi3_s.o _mulvdi3_s.o _negvsi2_s.o _negvdi2_s.o
_ctors_s.o _ffssi2_s.o _ffsdi2_s.o _clz_s.o _clzsi2_s.o _clzdi2_s.o
_ctzsi2_s.o _ctzdi2_s.o _popcount_tab_s.o _popcountsi2_s.o
_popcountdi2_s.o _paritysi2_s.o _paritydi2_s.o _powisf2_s.o _powidf2_s.o
_powixf2_s.o _mulhc3_s.o _mulsc3_s.o _muldc3_s.o _mulxc3_s.o _divhc3_s.o
_divsc3_s.o _divdc3_s.o _divxc3_s.o _bswapsi2_s.o _bswapdi2_s.o
_clrsbsi2_s.o _clrsbdi2_s.o _fixunssfsi_s.o _fixunsdfsi_s.o
_fixunsxfsi_s.o _fixsfdi_s.o _fixdfdi_s.o _fixxfdi_s.o _fixunssfdi_s.o
_fixunsdfdi_s.o _fixunsxfdi_s.o _floatdisf_s.o _floatdidf_s.o
_floatdixf_s.o _floatundisf_s.o _floatundidf_s.o _floatundixf_s.o
_divdi3_s.o _moddi3_s.o _divmoddi4_s.o _udivdi3_s.o _umoddi3_s.o
_udivmoddi4_s.o _udiv_w_sdiv_s.o sfp-exceptions_s.o addtf3_s.o
divtf3_s.o multf3_s.o negtf2_s.o subtf3_s.o unordtf2_s.o fixtfsi_s.o
fixunstfsi_s.o floatsitf_s.o floatunsitf_s.o fixtfdi_s.o fixunstfdi_s.o
floatditf_s.o floatunditf_s.o fixtfti_s.o fixunstfti_s.o floattitf_s.o
floatuntitf_s.o extendsftf2_s.o extenddftf2_s.o extendxftf2_s.o
trunctfsf2_s.o trunctfdf2_s.o trunctfxf2_s.o getf2_s.o letf2_s.o
eqtf2_s.o _divtc3_s.o _multc3_s.o _powitf2_s.o enable-execute-stack_s.o
unwind-dw2_s.o unwind-dw2-fde-dip_s.o unwind-sjlj_s.o unwind-c_s.o
emutls_s.o libgcc.a -lc
```

in my build directory under `x86_64-unknown-linux-musl/libgcc` which
fails with:
```
/root/mnt/tools/lib/gcc/x86_64-unknown-linux-musl/10.1.0/../../../../x86_64-unknown-linux-musl/bin/ld:
/root/mnt/tools/lib/gcc/x86_64-unknown-linux-musl/10.1.0/../../../../x86_64-unknown-linux-musl/lib/Scrt1.o:
in function `_start_c':
Scrt1.c:(.text._start_c+0x1b): undefined reference to `main'
collect2: error: ld returned 1 exit status
```

I verified with objdump -t crt1.o and objdump -t Scrt1.o that these
object files define main, which they do.

Im pretty confused by now because the name libgcc suggests that it's a
library, which of course does not have a main method. Why is ld
expecting one? What is the build trying to do here?

[1]:
https://stackoverflow.com/questions/62803659/compiling-gcc-fails-while-trying-to-link-libgcc

Re: Compiling gcc fails while trying to link libgcc

[Jim Wilson]

On Thu, Jul 9, 2020 at 1:51 AM Peter Lamby via Gcc-help
<gcc-help@gcc.gnu.org> wrote:
> export CFLAGS=-pipe -march=native -fstack-protector-strong -fno-plt \
> -pie -fpie

You can't use -pie when linking a shared library.  So this isn't going
to work.  Also the -fno-plt is suspicious.  Can you compile a shared
library without plts?  The -fpie is clearly wrong too.  You need to do
this a different way.  Note that gcc has a configure option
--enable-default-pie which will produce pie output by default, but
won't pass -pie to the linker with -static, -shared, or -r.  And won't
add -fpie if -fpic was specified.

rohan:2242$ gcc -shared -fpic -o tmp.so tmp.c
rohan:2243$ gcc -shared -fpic -o tmp.so tmp.c -pie
/usr/lib/gcc/x86_64-linux-gnu/7/../../../x86_64-linux-gnu/Scrt1.o: In
function `_start':
(.text+0x20): undefined reference to `main'
collect2: error: ld returned 1 exit status
rohan:2244$

Jim

Re: Compiling gcc fails while trying to link libgcc

[Peter Lamby]

Hi Jim,

removing both pie flags did the trick. I removed the
fno-plt too. Thanks for your help.

I like the default flag for pie. This way I don't have to set them
via CFLAGS and have them break my library builds :)

Best
Peter

Am 11. Juli 2020 03:35:38 MESZ schrieb Jim Wilson <jimw@sifive.com>:
>On Thu, Jul 9, 2020 at 1:51 AM Peter Lamby via Gcc-help
><gcc-help@gcc.gnu.org> wrote:
>> export CFLAGS=-pipe -march=native -fstack-protector-strong -fno-plt \
>> -pie -fpie
>
>You can't use -pie when linking a shared library.  So this isn't going
>to work.  Also the -fno-plt is suspicious.  Can you compile a shared
>library without plts?  The -fpie is clearly wrong too.  You need to do
>this a different way.  Note that gcc has a configure option
>--enable-default-pie which will produce pie output by default, but
>won't pass -pie to the linker with -static, -shared, or -r.  And won't
>add -fpie if -fpic was specified.
>
>rohan:2242$ gcc -shared -fpic -o tmp.so tmp.c
>rohan:2243$ gcc -shared -fpic -o tmp.so tmp.c -pie
>/usr/lib/gcc/x86_64-linux-gnu/7/../../../x86_64-linux-gnu/Scrt1.o: In
>function `_start':
>(.text+0x20): undefined reference to `main'
>collect2: error: ld returned 1 exit status
>rohan:2244$
>
>Jim

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