From: Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>
To: Richard Henderson <richard.henderson@linaro.org>,
libc-alpha@sourceware.org
Cc: fweimer@redhat.com
Subject: Re: [RESEND PATCH] Makeconfig: Set pie-ccflag to -fPIE by default
Date: Fri, 26 Aug 2022 09:32:44 -0300 [thread overview]
Message-ID: <43f24a1f-6237-2f45-ec0e-2fea9367f0b3@linaro.org> (raw)
In-Reply-To: <20220825210103.2259134-1-richard.henderson@linaro.org>
On 25/08/22 18:01, Richard Henderson via Libc-alpha wrote:
> [ I never saw this arrive in the list archives.
> Trying again with my linaro address subscribed. ]
>
> We should default to the larger code model, in order to support
> larger applications built with -static -pie. This should be
> consistent with pic-ccflag, which defaults to -fPIC.
>
> Remove the now redundant override from sysdeps/sparc/Makefile.
> Note that -fno-pie and -fno-PIE have the same effect.
>
> ---
>
> In the case of AArch64, the code changes are small but significant:
>
> 0000000000000000 <__libc_init_first>:
> 0: a9bd7bfd stp x29, x30, [sp, #-48]!
> - 4: 90000003 adrp x3, 0 <_GLOBAL_OFFSET_TABLE_>
> - 4: R_AARCH64_ADR_PREL_PG_HI21 _GLOBAL_OFFSET_TABLE_
> + 4: 90000003 adrp x3, 0 <__environ>
> + 4: R_AARCH64_ADR_GOT_PAGE __environ
> 8: 90000004 adrp x4, 0 <__libc_init_first>
> 8: R_AARCH64_ADR_PREL_PG_HI21 .bss
> c: 910003fd mov x29, sp
> 10: f9400063 ldr x3, [x3]
> - 10: R_AARCH64_LD64_GOTPAGE_LO15 __environ
> + 10: R_AARCH64_LD64_GOT_LO12_NC __environ
>
> In the small model, we are constrained to 15 bits of GOT, with a
> single shared base, _GLOBAL_OFFSET_TABLE_. In the large model,
> each symbol has a page + offset pair. For small functions like
> this, where there are no other variable references to share the
> common GOT pointer, there is no actual code change.
>
> r~
I recall that powerpc wanted to use -mcmodel=large, but it would require to
adjust a lot of assembly implementations. Are we sure this change does not
trigger any regression with current glibc code?
> ---
> Makeconfig | 2 +-
> sysdeps/sparc/Makefile | 3 ---
> 2 files changed, 1 insertion(+), 4 deletions(-)
>
> diff --git a/Makeconfig b/Makeconfig
> index e78cf220af..f8164a0025 100644
> --- a/Makeconfig
> +++ b/Makeconfig
> @@ -1052,7 +1052,7 @@ pic-ccflag = -fPIC
> PIC-ccflag = -fPIC
> endif
> # This can be changed by a sysdep makefile
> -pie-ccflag = -fpie
> +pie-ccflag = -fPIE
> no-pie-ccflag = -fno-pie
> # This one should always stay like this unless there is a very good reason.
> PIE-ccflag = -fPIE
> diff --git a/sysdeps/sparc/Makefile b/sysdeps/sparc/Makefile
> index 12c2c1b085..26b4a84606 100644
> --- a/sysdeps/sparc/Makefile
> +++ b/sysdeps/sparc/Makefile
> @@ -1,9 +1,6 @@
> # The Sparc `long double' is a distinct type we support.
> long-double-fcts = yes
>
> -pie-ccflag = -fPIE
> -no-pie-ccflag = -fno-PIE
> -
> ifeq ($(subdir),gmon)
> sysdep_routines += sparc-mcount
> endif
next prev parent reply other threads:[~2022-08-26 12:32 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-25 21:01 Richard Henderson
2022-08-26 12:32 ` Adhemerval Zanella Netto [this message]
2022-08-26 17:29 ` Richard Henderson
2022-08-26 18:39 Wilco Dijkstra
2022-08-26 19:02 ` H.J. Lu
2022-08-26 19:45 ` Richard Henderson
2022-08-26 20:11 ` H.J. Lu
2022-08-29 11:49 ` Wilco Dijkstra
2022-08-29 13:10 ` Florian Weimer
2022-08-29 15:27 ` Wilco Dijkstra
2022-08-29 15:27 ` Wilco Dijkstra
2022-08-29 19:43 ` H.J. Lu
2022-08-29 19:57 ` Fangrui Song
2022-09-05 8:58 ` Wilco Dijkstra
2022-09-15 21:45 ` Fangrui Song
2022-09-20 13:59 ` Wilco Dijkstra
2022-09-20 14:12 ` Florian Weimer
2022-09-20 16:00 ` Wilco Dijkstra
2022-09-20 22:02 ` Fangrui Song
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