[PATCH 2/3] elf: Replace a --defsym trick with an object file to be compatible with lld
Adhemerval Zanella
adhemerval.zanella@linaro.org
Fri Jan 29 14:38:53 GMT 2021
On 27/01/2021 22:03, Fāng-ruì Sòng via Libc-alpha wrote:
> On Wed, Jan 20, 2021 at 10:51 AM Fāng-ruì Sòng <maskray@google.com> wrote:
>>
>> On Tue, Jan 19, 2021 at 4:31 AM H.J. Lu <hjl.tools@gmail.com> wrote:
>>>
>>> On Tue, Jan 19, 2021 at 12:50 AM Fāng-ruì Sòng <maskray@google.com> wrote:
>>>>
>>>> On Mon, Jan 18, 2021 at 4:04 PM H.J. Lu <hjl.tools@gmail.com> wrote:
>>>>>
>>>>> On Mon, Dec 28, 2020 at 11:50 AM Fangrui Song via Libc-alpha
>>>>> <libc-alpha@sourceware.org> wrote:
>>>>>>
>>>>>> The existing code specifies -Wl,--defsym=malloc=0 and other malloc.os
>>>>>> definitions before libc_pic.a so that libc_pic.a(malloc.os) is not
>>>>>> fetched. This trick is used to avoid multiple definition errors which
>>>>>> would happen as a chain result:
>>>>>>
>>>>>> dl-allobjs.os has an undefined __libc_scratch_buffer_set_array_size
>>>>>> __libc_scratch_buffer_set_array_size fetches libc_pic.a(scratch_buffer_set_array_size.os)
>>>>>> libc_pic.a(scratch_buffer_set_array_size.os) has an undefined free
>>>>>> free fetches libc_pic.a(malloc.os)
>>>>>> libc_pic.a(malloc.os) has an undefined __libc_message
>>>>>> __libc_message fetches libc_pic.a(libc_fatal.os)
>>>>>>
>>>>>> libc_fatal.os will cause a multiple definition error (__GI___libc_fatal)
>>>>>> >>> defined at dl-fxstatat64.c
>>>>>> >>> /tmp/p/glibc/Release/elf/dl-allobjs.os:(__GI___libc_fatal)
>>>>>> >>> defined at libc_fatal.c
>>>>>> >>> libc_fatal.os:(.text+0x240) in archive /tmp/p/glibc/Release/libc_pic.a
>>>>>>
>>>>>> lld processes --defsym after all input files, so this trick does not
>>>>>> suppress multiple definition errors with lld. Split the step into two
>>>>>> and use an object file to make the intention more obvious and make lld
>>>>>> work.
>>>>>>
>>>>>> This is conceptually more appropriate because --defsym defines a SHN_ABS
>>>>>> symbol while a normal definition is relative to the image base.
>>>>>>
>>>>>
>>>>> This is irrelevant since --defsym was used to create a temporary file which was
>>>>> removed immediately after it was created:
>>>>>
>>>>> /usr/bin/gcc -nostdlib -nostartfiles -r -o
>>>>> /export/users/hjl/build/gnu/tools-build/glibc-gitlab/build-x86_64-linux/elf/librtld.map.o
>>>>> -Wl,--defsym=calloc=0 -Wl,--defsym=free=0 -Wl,--defsym=malloc=0
>>>>> -Wl,--defsym=realloc=0 -Wl,--defsym=__stack_chk_fail=0
>>>>> -Wl,--defsym=__stack_chk_fail_local=0 \
>>>>> '-Wl,-('
>>>>> /export/users/hjl/build/gnu/tools-build/glibc-gitlab/build-x86_64-linux/elf/dl-allobjs.os
>>>>> /export/users/hjl/build/gnu/tools-build/glibc-gitlab/build-x86_64-linux/libc_pic.a
>>>>> -lgcc '-Wl,-)' -Wl,-Map,/export/users/hjl/build/gnu/tools-build/glibc-gitlab/build-x86_64-linux/elf/librtld.mapT
>>>>> rm -f /export/users/hjl/build/gnu/tools-build/glibc-gitlab/build-x86_64-linux/elf/librtld.map.o
>>>>> mv -f /export/users/hjl/build/gnu/tools-build/glibc-gitlab/build-x86_64-linux/elf/librtld.mapT
>>>>> /export/users/hjl/build/gnu/tools-build/glibc-gitlab/build-x86_64-linux/elf/librtld.map
>>>>>
>>>>>> ---
>>>>>> elf/Makefile | 11 ++++-------
>>>>>> 1 file changed, 4 insertions(+), 7 deletions(-)
>>>>>>
>>>>>> diff --git a/elf/Makefile b/elf/Makefile
>>>>>> index 0b4d78c874..299bf24b49 100644
>>>>>> --- a/elf/Makefile
>>>>>> +++ b/elf/Makefile
>>>>>> @@ -524,10 +524,6 @@ rtld-stubbed-symbols = \
>>>>>> malloc \
>>>>>> realloc \
>>>>>>
>>>>>> -# The GCC arguments that implement $(rtld-stubbed-symbols).
>>>>>> -rtld-stubbed-symbols-args = \
>>>>>> - $(patsubst %,-Wl$(comma)--defsym=%=0, $(rtld-stubbed-symbols))
>>>>>> -
>>>>>> ifeq ($(have-ssp),yes)
>>>>>> # rtld is not built with the stack protector, so these references will
>>>>>> # go away in the rebuilds.
>>>>>> @@ -536,9 +532,10 @@ endif
>>>>>>
>>>>>> $(objpfx)librtld.map: $(objpfx)dl-allobjs.os $(common-objpfx)libc_pic.a
>>>>>> @-rm -f $@T
>>>>>> - $(reloc-link) -o $@.o $(rtld-stubbed-symbols-args) \
>>>>>> - '-Wl,-(' $^ -lgcc '-Wl,-)' -Wl,-Map,$@T
>>>>>> - rm -f $@.o
>>>>>> + echo '$(patsubst %,.globl %;,$(rtld-stubbed-symbols)) $(patsubst %,%:,$(rtld-stubbed-symbols))' | \
>>>>>> + $(CC) -o $@T.o $(ASFLAGS) -c -x assembler -
>>>>>
>>>>> Please generate
>>>>>
>>>>> .globl symbol;
>>>>> symbol = 0;
>>>>>
>>>>> to make it closer to -Wl,--defsym=symbol=0.
>>>>
>>>> If symbol: and symbol = 0; work, isn't symbol: slightly better because
>>>> it looks more normal?
>>>> Or is the intention here using SHN_ABS to make it clear these symbols
>>>> are special?
>>>
>>> Generate machine independent assembly codes is tricky. We should
>>> make before and after the change as close as possible to avoid ANY
>>> surprises. BTW, you need to check HAVE_ASM_SET_DIRECTIVE
>>> to decide using ".set" vs "=".
>>>
>>> --
>>> H.J.
>>
>> Thanks for the tip. In this case I think the patch as is (sticking
>> with `foo:`, don't use `foo = 0` or set) is better.
>> foo: works everywhere.
>
> Ping. I think the patch as-is is better than the alternative approach
> using either `=` or `.set`.
The patch breaks both arc-linux-gnuhf and hppa-linux-gnu with recent
ld.bfd 2.26, as below.
We will need to sort these out.
arc-linux-gnuhf:
make[2]: Entering directory '/home/azanella/glibc/glibc-git/elf'
echo '.globl calloc; .globl free; .globl malloc; .globl realloc; .globl __stack_chk_fail; .globl __stack_chk_fail_local; calloc: free: malloc: realloc: __stack_chk_fail: __stack_chk_fail_local:' | \
/home/azanella/toolchain/install/compilers/arc-linux-gnuhf/bin/arc-glibc-linux-gnuhf-gcc -o /home/azanella/glibc/build/arc-linux-gnuhf/elf/librtld.mapT.o -g -Werror=undef -Wa,--noexecstack -c -x assembler -
/home/azanella/toolchain/install/compilers/arc-linux-gnuhf/bin/arc-glibc-linux-gnuhf-gcc -nostdlib -nostartfiles -r -o /home/azanella/glibc/build/arc-linux-gnuhf/elf/librtld.map.o /home/azanella/glibc/build/arc-linux-gnuhf/elf/librtld.mapT.o '-Wl,-(' /home/azanella/glibc/build/arc-linux-gnuhf/elf/dl-allobjs.os /home/azanella/glibc/build/arc-linux-gnuhf/libc_pic.a -lgcc '-Wl,-)' -Wl,-Map,/home/azanella/glibc/build/arc-linux-gnuhf/elf/librtld.mapT
/home/azanella/toolchain/install/compilers/arc-linux-gnuhf/lib/gcc/arc-glibc-linux-gnuhf/10.2.1/../../../../arc-glibc-linux-gnuhf/bin/ld: /home/azanella/glibc/build/arc-linux-gnuhf/libc_pic.a(sbrk.os): in function `__GI___sbrk':
/home/azanella/glibc/glibc-git/misc/sbrk.c:37: multiple definition of `__sbrk'; /home/azanella/glibc/build/arc-linux-gnuhf/elf/dl-allobjs.os:/home/azanella/glibc/glibc-git/elf/../misc/sbrk.c:37: first defined here
/home/azanella/toolchain/install/compilers/arc-linux-gnuhf/lib/gcc/arc-glibc-linux-gnuhf/10.2.1/../../../../arc-glibc-linux-gnuhf/bin/ld: /home/azanella/glibc/build/arc-linux-gnuhf/libc_pic.a(libc_fatal.os): in function `__GI___libc_fatal':
/home/azanella/glibc/glibc-git/libio/../sysdeps/posix/libc_fatal.c:161: multiple definition of `__GI___libc_fatal'; /home/azanella/glibc/build/arc-linux-gnuhf/elf/dl-allobjs.os:/home/azanella/glibc/glibc-git/elf/dl-minimal.c:267: first defined here
/home/azanella/toolchain/install/compilers/arc-linux-gnuhf/lib/gcc/arc-glibc-linux-gnuhf/10.2.1/../../../../arc-glibc-linux-gnuhf/bin/ld: /home/azanella/glibc/build/arc-linux-gnuhf/libc_pic.a(libc_fatal.os): in function `__GI___libc_fatal':
/home/azanella/glibc/glibc-git/libio/../sysdeps/posix/libc_fatal.c:161: multiple definition of `__libc_fatal'; /home/azanella/glibc/build/arc-linux-gnuhf/elf/dl-allobjs.os:/home/azanella/glibc/glibc-git/elf/dl-minimal.c:267: first defined here
/home/azanella/toolchain/install/compilers/arc-linux-gnuhf/lib/gcc/arc-glibc-linux-gnuhf/10.2.1/../../../../arc-glibc-linux-gnuhf/bin/ld: /home/azanella/glibc/build/arc-linux-gnuhf/libc_pic.a(_itoa.os): in function `_itoa':
/home/azanella/glibc/glibc-git/stdio-common/_itoa.c:196: multiple definition of `_itoa'; /home/azanella/glibc/build/arc-linux-gnuhf/elf/dl-allobjs.os:/home/azanella/glibc/glibc-git/elf/dl-minimal.c:323: first defined here
/home/azanella/toolchain/install/compilers/arc-linux-gnuhf/lib/gcc/arc-glibc-linux-gnuhf/10.2.1/../../../../arc-glibc-linux-gnuhf/bin/ld: /home/azanella/glibc/build/arc-linux-gnuhf/libc_pic.a(getcwd.os): in function `__GI___getcwd':
/home/azanella/glibc/glibc-git/io/../sysdeps/unix/sysv/linux/getcwd.c:50: multiple definition of `__getcwd'; /home/azanella/glibc/build/arc-linux-gnuhf/elf/dl-allobjs.os:/home/azanella/glibc/glibc-git/elf/../sysdeps/unix/sysv/linux/getcwd.c:50: first defined here
/home/azanella/toolchain/install/compilers/arc-linux-gnuhf/lib/gcc/arc-glibc-linux-gnuhf/10.2.1/../../../../arc-glibc-linux-gnuhf/bin/ld: /home/azanella/glibc/build/arc-linux-gnuhf/libc_pic.a(dl-error.os): in function `__GI__dl_signal_exception':
/home/azanella/glibc/glibc-git/elf/dl-error-skeleton.c:91: multiple definition of `_dl_signal_exception'; /home/azanella/glibc/build/arc-linux-gnuhf/elf/dl-allobjs.os:/home/azanella/glibc/glibc-git/elf/dl-error-skeleton.c:91: first defined here
/home/azanella/toolchain/install/compilers/arc-linux-gnuhf/lib/gcc/arc-glibc-linux-gnuhf/10.2.1/../../../../arc-glibc-linux-gnuhf/bin/ld: /home/azanella/glibc/build/arc-linux-gnuhf/libc_pic.a(dl-error.os): in function `__GI__dl_signal_error':
/home/azanella/glibc/glibc-git/elf/dl-error-skeleton.c:109: multiple definition of `_dl_signal_error'; /home/azanella/glibc/build/arc-linux-gnuhf/elf/dl-allobjs.os:/home/azanella/glibc/glibc-git/elf/dl-error-skeleton.c:109: first defined here
/home/azanella/toolchain/install/compilers/arc-linux-gnuhf/lib/gcc/arc-glibc-linux-gnuhf/10.2.1/../../../../arc-glibc-linux-gnuhf/bin/ld: /home/azanella/glibc/build/arc-linux-gnuhf/libc_pic.a(dl-error.os): in function `__GI__dl_catch_exception':
/home/azanella/glibc/glibc-git/elf/dl-error-skeleton.c:175: multiple definition of `_dl_catch_exception'; /home/azanella/glibc/build/arc-linux-gnuhf/elf/dl-allobjs.os:/home/azanella/glibc/glibc-git/elf/dl-error-skeleton.c:175: first defined here
/home/azanella/toolchain/install/compilers/arc-linux-gnuhf/lib/gcc/arc-glibc-linux-gnuhf/10.2.1/../../../../arc-glibc-linux-gnuhf/bin/ld: /home/azanella/glibc/build/arc-linux-gnuhf/libc_pic.a(dl-error.os): in function `__GI__dl_catch_error':
/home/azanella/glibc/glibc-git/elf/dl-error-skeleton.c:225: multiple definition of `_dl_catch_error'; /home/azanella/glibc/build/arc-linux-gnuhf/elf/dl-allobjs.os:/home/azanella/glibc/glibc-git/elf/dl-error-skeleton.c:225: first defined here
collect2: error: ld returned 1 exit status
make[2]: *** [Makefile:538: /home/azanella/glibc/build/arc-linux-gnuhf/elf/librtld.map] Error 1
hppa-linux-gnu:
echo '.globl calloc; .globl free; .globl malloc; .globl realloc; calloc: free: malloc: realloc:' | \
/home/azanella/toolchain/install/compilers/hppa-linux-gnu/bin/hppa-glibc-linux-gnu-gcc -o /home/azanella/glibc/build/hppa-linux-gnu/elf/librtld.mapT.o -g -Werror=undef -c -x assembler -
/home/azanella/toolchain/install/compilers/hppa-linux-gnu/bin/hppa-glibc-linux-gnu-gcc -nostdlib -nostartfiles -r -o /home/azanella/glibc/build/hppa-linux-gnu/elf/librtld.map.o /home/azanella/glibc/build/hppa-linux-gnu/elf/librtld.mapT.o '-Wl,-(' /home/azanella/glibc/build/hppa-linux-gnu/elf/dl-allobjs.os /home/azanella/glibc/build/hppa-linux-gnu/libc_pic.a -lgcc '-Wl,-)' -Wl,-Map,/home/azanella/glibc/build/hppa-linux-gnu/elf/librtld.mapT
/home/azanella/toolchain/install/compilers/hppa-linux-gnu/lib/gcc/hppa-glibc-linux-gnu/10.2.1/../../../../hppa-glibc-linux-gnu/bin/ld: /home/azanella/glibc/build/hppa-linux-gnu/libc_pic.a(sbrk.os): in function `__GI___sbrk':
/home/azanella/glibc/glibc-git/misc/sbrk.c:37: multiple definition of `__sbrk'; /home/azanella/glibc/build/hppa-linux-gnu/elf/dl-allobjs.os:/home/azanella/glibc/glibc-git/elf/../misc/sbrk.c:37: first defined here
/home/azanella/toolchain/install/compilers/hppa-linux-gnu/lib/gcc/hppa-glibc-linux-gnu/10.2.1/../../../../hppa-glibc-linux-gnu/bin/ld: /home/azanella/glibc/build/hppa-linux-gnu/libc_pic.a(libc_fatal.os): in function `__GI___libc_fatal':
/home/azanella/glibc/glibc-git/libio/../sysdeps/posix/libc_fatal.c:161: multiple definition of `__GI___libc_fatal'; /home/azanella/glibc/build/hppa-linux-gnu/elf/dl-allobjs.os:/home/azanella/glibc/glibc-git/elf/dl-minimal.c:268: first defined here
/home/azanella/toolchain/install/compilers/hppa-linux-gnu/lib/gcc/hppa-glibc-linux-gnu/10.2.1/../../../../hppa-glibc-linux-gnu/bin/ld: /home/azanella/glibc/build/hppa-linux-gnu/libc_pic.a(libc_fatal.os): in function `__GI___libc_fatal':
/home/azanella/glibc/glibc-git/libio/../sysdeps/posix/libc_fatal.c:161: multiple definition of `__libc_fatal'; /home/azanella/glibc/build/hppa-linux-gnu/elf/dl-allobjs.os:/home/azanella/glibc/glibc-git/elf/dl-minimal.c:268: first defined here
/home/azanella/toolchain/install/compilers/hppa-linux-gnu/lib/gcc/hppa-glibc-linux-gnu/10.2.1/../../../../hppa-glibc-linux-gnu/bin/ld: /home/azanella/glibc/build/hppa-linux-gnu/libc_pic.a(_itoa.os): in function `_itoa':
/home/azanella/glibc/glibc-git/stdio-common/_itoa.c:196: multiple definition of `_itoa'; /home/azanella/glibc/build/hppa-linux-gnu/elf/dl-allobjs.os:/home/azanella/glibc/glibc-git/elf/dl-minimal.c:323: first defined here
/home/azanella/toolchain/install/compilers/hppa-linux-gnu/lib/gcc/hppa-glibc-linux-gnu/10.2.1/../../../../hppa-glibc-linux-gnu/bin/ld: /home/azanella/glibc/build/hppa-linux-gnu/libc_pic.a(getcwd.os): in function `__GI___getcwd':
/home/azanella/glibc/glibc-git/io/../sysdeps/unix/sysv/linux/getcwd.c:50: multiple definition of `__getcwd'; /home/azanella/glibc/build/hppa-linux-gnu/elf/dl-allobjs.os:/home/azanella/glibc/glibc-git/elf/../sysdeps/unix/sysv/linux/getcwd.c:50: first defined here
/home/azanella/toolchain/install/compilers/hppa-linux-gnu/lib/gcc/hppa-glibc-linux-gnu/10.2.1/../../../../hppa-glibc-linux-gnu/bin/ld: /home/azanella/glibc/build/hppa-linux-gnu/libc_pic.a(dl-error.os): in function `__GI__dl_signal_exception':
/home/azanella/glibc/glibc-git/elf/dl-error-skeleton.c:91: multiple definition of `_dl_signal_exception'; /home/azanella/glibc/build/hppa-linux-gnu/elf/dl-allobjs.os:/home/azanella/glibc/glibc-git/elf/dl-error-skeleton.c:91: first defined here
/home/azanella/toolchain/install/compilers/hppa-linux-gnu/lib/gcc/hppa-glibc-linux-gnu/10.2.1/../../../../hppa-glibc-linux-gnu/bin/ld: /home/azanella/glibc/build/hppa-linux-gnu/libc_pic.a(dl-error.os): in function `__GI__dl_signal_error':
/home/azanella/glibc/glibc-git/elf/dl-error-skeleton.c:109: multiple definition of `_dl_signal_error'; /home/azanella/glibc/build/hppa-linux-gnu/elf/dl-allobjs.os:/home/azanella/glibc/glibc-git/elf/dl-error-skeleton.c:109: first defined here
/home/azanella/toolchain/install/compilers/hppa-linux-gnu/lib/gcc/hppa-glibc-linux-gnu/10.2.1/../../../../hppa-glibc-linux-gnu/bin/ld: /home/azanella/glibc/build/hppa-linux-gnu/libc_pic.a(dl-error.os): in function `__GI__dl_catch_exception':
/home/azanella/glibc/glibc-git/elf/dl-error-skeleton.c:175: multiple definition of `_dl_catch_exception'; /home/azanella/glibc/build/hppa-linux-gnu/elf/dl-allobjs.os:/home/azanella/glibc/glibc-git/elf/dl-error-skeleton.c:175: first defined here
/home/azanella/toolchain/install/compilers/hppa-linux-gnu/lib/gcc/hppa-glibc-linux-gnu/10.2.1/../../../../hppa-glibc-linux-gnu/bin/ld: /home/azanella/glibc/build/hppa-linux-gnu/libc_pic.a(dl-error.os): in function `__GI__dl_catch_error':
/home/azanella/glibc/glibc-git/elf/dl-error-skeleton.c:225: multiple definition of `_dl_catch_error'; /home/azanella/glibc/build/hppa-linux-gnu/elf/dl-allobjs.os:/home/azanella/glibc/glibc-git/elf/dl-error-skeleton.c:225: first defined here
collect2: error: ld returned 1 exit status
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