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[Bug dynamic-link/21598] i386 _dl_runtime_resolve/_dl_runtime_profile is incompatible with shadow stack

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The branch, hjl/cet/pr21598 has been created
        at  26bb65e293df8d6a042bf3d51d0a4d2f313f4eb5 (commit)

- Log -----------------------------------------------------------------;h=26bb65e293df8d6a042bf3d51d0a4d2f313f4eb5

commit 26bb65e293df8d6a042bf3d51d0a4d2f313f4eb5
Author: H.J. Lu <>
Date:   Thu Jun 22 08:51:42 2017 -0700

    x86: Add IBT/SHSTK bits to cpu-features

    Add IBT/SHSTK bits to cpu-features for Shadow Stack in Intel Control-flow
    Enforcement Technology (CET) instructions:

        * sysdeps/x86/cpu-features.h (bit_cpu_BIT): New.
        (bit_cpu_SHSTK): Likewise.
        (index_cpu_IBT): Likewise.
        (index_cpu_SHSTK): Likewise.
        (reg_IBT): Likewise.
        (reg_SHSTK): Likewise.
        * sysdeps/x86/cpu-tunables.c (TUNABLE_CALLBACK (set_hwcaps)):
        Handle index_cpu_IBT and index_cpu_SHSTK.;h=6bd5c7a0dedf99a48a5a91d008669f5e9d15ab2e

commit 6bd5c7a0dedf99a48a5a91d008669f5e9d15ab2e
Author: H.J. Lu <>
Date:   Fri Aug 11 15:36:08 2017 +0200

    Add private_function for private functions within glibc [BZ #21598]

    USE_REGPARMS in is only used to control how parameters are
    passed for internal functions on i386.  On i386, we define

     #define internal_function __attribute__ ((regparm (3), stdcall))

    so that we pass up to 3 integer parameters in registers for internal
    functuons on i386.  i386 has


            movl (%esp), %ecx
            movl %eax, (%esp)       # Store the function address.
            movl 4(%esp), %eax
            ret $12                 # Jump to function address.

    which is incompatible with Shadow Stack in Intel Control-flow Enforcement
    Technology (CET) instructions:

    since shadow stack doesn't match return stack.  We need to use register
    indirect branch via %ecx.  That means only 2 parameters can be passed
    in registers for external function calls with lazy binding when shadow
    stack is enabled.  However, internal_function, which should be used only
    with hidden function within, are also used with private function
    calls between different shared objects of glibc.

    This patch removes USE_REGPARMS and internal_function from
    It adds a new header file, function-attrs.h, to define internal_function
    and private_function, which is for private function calls between
    different shared objects.  Currently, sysdeps/i386/function-attrs.h
    defines private_function as

     #define private_function __attribute__ ((regparm (3), stdcall))

    There is no change in shared objects on Linux/i686 nor Linux/x86_64.

    When shadow stack is enabled, private_function will be defined as

     #define private_function __attribute__ ((regparm (2), stdcall))

    so that %ecx can be used as scratch register by _dl_runtime_resolve.

        [BZ #21598]
        * (USE_REGPARMS): Removed.
        (internal_function): Likewise.
        * debug/fortify_fail.c (__fortify_fail): Replace internal_function
        with private_function.
        * elf/dl-addr.c (_dl_addr): Likewise.
        * elf/dl-error-skeleton.c (_dl_signal_error): Likewise.
        (_dl_catch_error): Likewise.
        * elf/dl-execstack.c (_dl_make_stack_executable): Likewise.
        * elf/dl-load.c (_dl_rtld_di_serinfo): Likewise.
        * elf/dl-open.c (_dl_find_dso_for_object): Likewise.
        * elf/dl-support.c (_dl_make_stack_executable_hook): Likewise.
        * elf/dl-sym.c (_dl_vsym): Likewise.
        (_dl_sym): Likewise.
        * elf/dl-tls.c (_dl_get_tls_static_info): Likewise.
        (_dl_allocate_tls_init): Likewise.
        (_dl_allocate_tls): Likewise.
        (_dl_deallocate_tls): Likewise.
        * grp/grp-merge.c (__copy_grp): Likewise.
        (__merge_grp): Likewise.
        * grp/grp-merge.h (__copy_grp): Likewise.
        (__merge_grp): Likewise.
        * include/dlfcn.h (_dl_addr): Likewise.
        (_dl_sym): Likewise.
        (_dl_vsym): Likewise.
        * include/rpc/pmap_clnt.h (__libc_rpc_getport): Likewise.
        * include/stdio.h (__fortify_fail): Likewise.
        * include/stdlib.h (__strtof_nan): Likewise.
        (__strtod_nan): Likewise.
        (__strtold_nan): Likewise.
        (__wcstof_nan): Likewise.
        (__wcstod_nan): Likewise.
        (__wcstold_nan): Likewise.
        (__strtof128_nan): Likewise.
        (__wcstof128_nan): Likewise.
        * nptl/allocatestack.c (__make_stacks_executable): Likewise.
        * nptl/libc_pthread_init.c (__libc_pthread_init): Likewise.
        * nptl/pthreadP.h (__make_stacks_executable): Likewise.
        (__libc_pthread_init): Likewise.
        * nss/XXX-lookup.c (DB_LOOKUP_FCT): Likewise.
        (DB_COMPAT_FCT): Likewise.
        * nss/getXXbyYY_r.c (DB_LOOKUP_FCT): Likewise.
        * nss/getXXent_r.c (DB_LOOKUP_FCT): Likewise.
        * nss/nsswitch.h (db_lookup_function): Likewise.
        * resolv/gai_misc.h (__gai_sigqueue): Likewise.
        * resolv/gai_sigqueue.c (__gai_sigqueue): Likewise.
        * stdlib/strtod_nan_main.c (STRTOD_NAN): Likewise.
        * sunrpc/pm_getport.c (__libc_rpc_getport): Likewise.
        * sysdeps/generic/ldsodefs.h (_dl_make_stack_executable_hook):
        (_dl_make_stack_executable): Likewise.
        (_dl_signal_error): Likewise.
        (_dl_catch_error): Likewise.
        (_dl_rtld_di_serinfo): Likewise.
        (_dl_allocate_tls): Likewise.
        (_dl_get_tls_static_info): Likewise.
        (_dl_allocate_tls_init): Likewise.
        (_dl_deallocate_tls): Likewise.
        (_dl_find_dso_for_object): Likewise.
        * sysdeps/unix/sysv/linux/dl-execstack.c
        (_dl_make_stack_executable): Likewise.
        * sysdeps/unix/sysv/linux/gai_sigqueue.c (__gai_sigqueue):
        * sysdeps/unix/sysv/linux/netlink_assert_response.c
        (__netlink_assert_response): Likewise.
        * sysdeps/unix/sysv/linux/netlinkaccess.h
        (__netlink_assert_response): Likewise.
        * include/libc-symbols.h (internal_function): Removed.
        Include <function-attrs.h>.
        * sysdeps/generic/function-attrs.h: New file.
        * sysdeps/i386/function-attrs.h: Likewise.
        * sysdeps/i386/ (USE_REGPARMS): Removed.
        * sysdeps/i386/configure: Regenerated.


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