llvm dev - Jun 2020 - LLD : __start_ and __end_ symbols for orphan sections

You are right it creates them but sets the protected flag (STV_PROTECTED) which
seems to be the cause of my problem.
How can I tell it to set the flag as STV_DEFAULT?

Thanks
A

On 5/28/20, 11:30 PM, "Fangrui Song" <maskray at google.com>
wrote:

    NetApp Security WARNING: This is an external email. Do not click links or
open attachments unless you recognize the sender and know the content is safe.




    On 2020-05-28, Moshtaghi, Alireza via llvm-dev wrote:
    >lld does not seem to create the __start and __end symbols for orphan
sections.
    >I would like to keep my linker script as generic as possible so how can
I tell lld to create these symbols without having to add them in the linker
script?
    >
    >Thanks
    >A

    It works for me.

    SECTIONS {
       data : { *(data) }
    }

    .section data,"aw"
    .quad __start_orphan
    .quad __stop_orphan

    .section orphan,"aw"
    .quad __start_data
    .quad __stop_data


    Can you give an example __start_ or __end_ symbols are not defined for
orphan sections?

Sorry for the cryptic code but I had to modify stuff from original
In the following example see the difference when you comment or uncomment the
line in the linker script:
============ test.c ============= :
struct orphan_dummy_anno_s {
 void (*func)(void);
};

static void dummy_export_dbg_log_init_f (void) __attribute__ ((unused));
static struct orphan_dummy_anno_s const
  dummy_export_dbg_log_init_linker_set   { dummy_export_dbg_log_init_f, };
__asm__ (".globl " "__start_set_orphan_dummy_anno");
__asm__ (".globl " "__stop_set_orphan_dummy_anno");
static void const
  *__set_orphan_dummy_anno_sym_dummy_export_dbg_log_init_linker_set
  __attribute__ ((__section__ ("set_" "orphan_dummy_anno")))
  __attribute__ ((__used__)) = &dummy_export_dbg_log_init_linker_set;
============ linker_script ============= :
SECTIONS {
   data : { *(data) }
# when commented, the __start and __stop symbols will be protected. How can I
keep it from setting it as protected?
#   set_orphan_dummy_anno : { PROVIDE(__start_set_orphan_dummy_anno = . );
*(set_orphan_dummy_anno) PROVIDE (__stop_set_orphan_dummy_anno = . );}
}
============ howto ============= :
LDFLAGS="-Bshareable -T ./linker_script"
clang -fPIC -c test.c
ld.lld $LDFLAGS test.o -o test.so
objdump -tT test.so


On 6/2/20, 12:00 AM, "llvm-dev on behalf of Moshtaghi, Alireza via
llvm-dev" <llvm-dev-bounces at lists.llvm.org on behalf of llvm-dev at
lists.llvm.org> wrote:

    NetApp Security WARNING: This is an external email. Do not click links or
open attachments unless you recognize the sender and know the content is safe.




    You are right it creates them but sets the protected flag (STV_PROTECTED)
which seems to be the cause of my problem.
    How can I tell it to set the flag as STV_DEFAULT?

    Thanks
    A

    On 5/28/20, 11:30 PM, "Fangrui Song" <maskray at google.com>
wrote:

        NetApp Security WARNING: This is an external email. Do not click links
or open attachments unless you recognize the sender and know the content is
safe.




        On 2020-05-28, Moshtaghi, Alireza via llvm-dev wrote:
        >lld does not seem to create the __start and __end symbols for orphan
sections.
        >I would like to keep my linker script as generic as possible so how
can I tell lld to create these symbols without having to add them in the linker
script?
        >
        >Thanks
        >A

        It works for me.

        SECTIONS {
           data : { *(data) }
        }

        .section data,"aw"
        .quad __start_orphan
        .quad __stop_orphan

        .section orphan,"aw"
        .quad __start_data
        .quad __stop_data


        Can you give an example __start_ or __end_ symbols are not defined for
orphan sections?

    _______________________________________________
    LLVM Developers mailing list
    llvm-dev at lists.llvm.org
    https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev

On 2020-06-02, Moshtaghi, Alireza wrote:
>Sorry for the cryptic code but I had to modify stuff from original
>In the following example see the difference when you comment or uncomment
the line in the linker script:
>============ test.c ============= :
>struct orphan_dummy_anno_s {
> void (*func)(void);
>};
>
>static void dummy_export_dbg_log_init_f (void) __attribute__ ((unused));
>static struct orphan_dummy_anno_s const
>  dummy_export_dbg_log_init_linker_set >  { dummy_export_dbg_log_init_f,
};
>__asm__ (".globl " "__start_set_orphan_dummy_anno");
>__asm__ (".globl " "__stop_set_orphan_dummy_anno");
>static void const
>  *__set_orphan_dummy_anno_sym_dummy_export_dbg_log_init_linker_set
>  __attribute__ ((__section__ ("set_"
"orphan_dummy_anno")))
>  __attribute__ ((__used__)) = &dummy_export_dbg_log_init_linker_set;
>============ linker_script ============= :
>SECTIONS {
>   data : { *(data) }
># when commented, the __start and __stop symbols will be protected. How can
I keep it from setting it as protected?
>#   set_orphan_dummy_anno : { PROVIDE(__start_set_orphan_dummy_anno = . );
*(set_orphan_dummy_anno) PROVIDE (__stop_set_orphan_dummy_anno = . );}
>}
>============ howto ============= :
>LDFLAGS="-Bshareable -T ./linker_script"
>clang -fPIC -c test.c
>ld.lld $LDFLAGS test.o -o test.so
>objdump -tT test.so
Making __start_* __stop_* STV_PROTECTED is a deliberate choice. See
https://reviews.llvm.org/D44566
Such symbols can still be exported to .dynsym (can be looked up from
another shared object with dlopen) but prevent accidental symbol
preemption..
>
>On 6/2/20, 12:00 AM, "llvm-dev on behalf of Moshtaghi, Alireza via
llvm-dev" <llvm-dev-bounces at lists.llvm.org on behalf of llvm-dev at
lists.llvm.org> wrote:
>
>    NetApp Security WARNING: This is an external email. Do not click links
or open attachments unless you recognize the sender and know the content is
safe.
>
>
>
>
>    You are right it creates them but sets the protected flag
(STV_PROTECTED) which seems to be the cause of my problem.
>    How can I tell it to set the flag as STV_DEFAULT?
>
>    Thanks
>    A
>
>    On 5/28/20, 11:30 PM, "Fangrui Song" <maskray at
google.com> wrote:
>
>        NetApp Security WARNING: This is an external email. Do not click
links or open attachments unless you recognize the sender and know the content
is safe.
>
>
>
>
>        On 2020-05-28, Moshtaghi, Alireza via llvm-dev wrote:
>        >lld does not seem to create the __start and __end symbols for
orphan sections.
>        >I would like to keep my linker script as generic as possible so
how can I tell lld to create these symbols without having to add them in the
linker script?
>        >
>        >Thanks
>        >A
>
>        It works for me.
>
>        SECTIONS {
>           data : { *(data) }
>        }
>
>        .section data,"aw"
>        .quad __start_orphan
>        .quad __stop_orphan
>
>        .section orphan,"aw"
>        .quad __start_data
>        .quad __stop_data
>
>
>        Can you give an example __start_ or __end_ symbols are not defined
for orphan sections?
>
>    _______________________________________________
>    LLVM Developers mailing list
>    llvm-dev at lists.llvm.org
>    https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>