From: Adhemerval Zanella <adhemerval.zanella@linaro.org>
To: Fangrui Song <maskray@google.com>,
libc-alpha@sourceware.org, Alan Modra <amodra@gmail.com>,
Tulio Magno Quites Machado Filho <tuliom@linux.ibm.com>
Subject: Re: [PATCH] elf: Replace PI_STATIC_AND_HIDDEN with opposite HIDDEN_VAR_NEEDS_DYNAMIC_RELOC
Date: Mon, 25 Apr 2022 14:53:06 -0300 [thread overview]
Message-ID: <fe72e62a-aef8-8002-ef78-a1a14d9b1068@linaro.org> (raw)
In-Reply-To: <fe0bde71-c39e-3ce6-5780-ead46716a2a1@linaro.org>
On 25/04/2022 13:40, Adhemerval Zanella wrote:
>
>
> On 25/04/2022 04:58, Fangrui Song wrote:
>> PI_STATIC_AND_HIDDEN indicates whether accesses to internal linkage
>> variables and hidden visibility variables in a shared object (ld.so)
>> need dynamic relocations (usually R_*_RELATIVE). PI (position
>> independent) in the macro name is a misnomer: a code sequence using GOT
>> is typically position-independent as well, but using dynamic relocations
>> does not meet the requirement.
>>
>> Not defining PI_STATIC_AND_HIDDEN is legacy and we expect that all new
>> ports will define PI_STATIC_AND_HIDDEN. Current ports defining
>> PI_STATIC_AND_HIDDEN are more than the opposite. Change the configure
>> default.
>>
>> No functional change.
>>
>> Note: HIDDEN_VAR_NEEDS_DYNAMIC_RELOC will be removed when Alan Modra's
>> powerpc64 static-pie work
>> (https://sourceware.org/pipermail/libc-alpha/2022-April/137987.html)
>> lands.
>
> I agree the macro naming is confusing and does not represent the intent
> is a straigthforward manner. Patch looks ok, but I have added some
> comments below.
>
>> ---
>> config.h.in | 6 +-
>> elf/rtld.c | 2 +-
>> sysdeps/aarch64/configure | 5 -
>> sysdeps/aarch64/configure.ac | 4 -
>> sysdeps/alpha/configure | 5 -
>> sysdeps/alpha/configure.ac | 4 -
>> sysdeps/arc/configure | 2 -
>> sysdeps/arc/configure.ac | 1 -
>> sysdeps/arm/configure | 3 -
>> sysdeps/arm/configure.ac | 5 -
>> sysdeps/csky/configure | 3 -
>> sysdeps/csky/configure.ac | 2 -
>> sysdeps/hppa/configure | 3 +
>> sysdeps/hppa/configure.ac | 2 +
>> sysdeps/ia64/configure | 3 -
>> sysdeps/ia64/configure.ac | 4 -
>> sysdeps/m68k/configure | 165 +++++++++++++++++++++++++
>> sysdeps/m68k/configure.ac | 6 +
>> sysdeps/microblaze/configure | 3 +
>> sysdeps/microblaze/configure.ac | 2 +
>> sysdeps/mips/configure | 2 +
>> sysdeps/mips/configure.ac | 2 +-
>> sysdeps/nios2/configure | 3 +
>> sysdeps/nios2/configure.ac | 2 +
>> sysdeps/or1k/configure | 3 -
>> sysdeps/or1k/configure.ac | 2 -
>> sysdeps/powerpc/powerpc32/configure | 3 +
>> sysdeps/powerpc/powerpc32/configure.ac | 2 +
>> sysdeps/powerpc/powerpc64/configure | 3 +
>> sysdeps/powerpc/powerpc64/configure.ac | 2 +
>> sysdeps/powerpc/tst-tlsifunc.c | 2 +-
>> sysdeps/riscv/configure | 3 -
>> sysdeps/riscv/configure.ac | 2 -
>> sysdeps/s390/configure | 3 -
>> sysdeps/s390/configure.ac | 4 -
>> sysdeps/sh/configure | 3 -
>> sysdeps/sh/configure.ac | 4 -
>> sysdeps/sparc/configure | 2 -
>> sysdeps/sparc/configure.ac | 2 -
>> sysdeps/x86/configure | 3 -
>> sysdeps/x86/configure.ac | 4 -
>> 41 files changed, 204 insertions(+), 82 deletions(-)
>> create mode 100644 sysdeps/m68k/configure
>> create mode 100644 sysdeps/m68k/configure.ac
>>
>> diff --git a/config.h.in b/config.h.in
>> index a94f756859..916465fce8 100644
>> --- a/config.h.in
>> +++ b/config.h.in
>> @@ -84,9 +84,9 @@
>> /* Define if the compiler\'s exception support is based on libunwind. */
>> #undef HAVE_CC_WITH_LIBUNWIND
>>
>> -/* Define if the access to static and hidden variables is position independent
>> - and does not need relocations. */
>> -#undef PI_STATIC_AND_HIDDEN
>> +/* Define if the accesses to static and hidden variables in a shared object
>> + need dynamic relocations. */
>> +#undef HIDDEN_VAR_NEEDS_DYNAMIC_RELOC
>>
>> /* Define this to disable the 'hidden_proto' et al macros in
>> include/libc-symbols.h that avoid PLT slots in PIE. */
>
> OK, naming make more sense now.
>
>> diff --git a/elf/rtld.c b/elf/rtld.c
>> index 19e328f89e..2174cc1da7 100644
>> --- a/elf/rtld.c
>> +++ b/elf/rtld.c
>> @@ -424,7 +424,7 @@ DL_SYSINFO_IMPLEMENTATION
>> is fine, too. The latter is important here. We can avoid setting
>> up a temporary link map for ld.so if we can mark _rtld_global as
>> hidden. */
>> -#ifdef PI_STATIC_AND_HIDDEN
>> +#ifndef HIDDEN_VAR_NEEDS_DYNAMIC_RELOC
>> # define DONT_USE_BOOTSTRAP_MAP 1
>> #endif
>>
>
> I think it would be better to now always assume the variable is defined:
>
> #if HIDDEN_VAR_NEEDS_DYNAMIC_RELOC
> # define HIDDEN_VAR_NEEDS_DYNAMIC_RELOC 1
> #endif
Thinking twice there is not how config.h work now so it is ok as is. The
only issue with the patch is only the m68k configure that seems bogus.
prev parent reply other threads:[~2022-04-25 17:53 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-25 7:58 Fangrui Song
2022-04-25 16:40 ` Adhemerval Zanella
2022-04-25 17:53 ` Adhemerval Zanella [this message]
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