[llvm-dev] LLD : __start_ and __end_ symbols for orphan sections

[Moshtaghi, Alireza via llvm-dev]

Okay
Thank you

On 6/2/20, 8:37 AM, "Fangrui Song" <maskray at google.com> wrote:

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    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:
    >
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    >
    >
    >
    >
    >    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?
    >
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