[PATCH v2 5/5] Linux: Consolidate auxiliary vector parsing
Adhemerval Zanella
adhemerval.zanella@linaro.org
Tue Feb 8 20:19:42 GMT 2022
On 03/02/2022 08:08, Florian Weimer via Libc-alpha wrote:
> And optimize it slightly.
>
> The large switch statement in _dl_sysdep_start can be replaced with
> a large array. This reduces source code and binary size. On
> i686-linux-gnu:
>
> Before:
>
> text data bss dec hex filename
> 7791 12 0 7803 1e7b elf/dl-sysdep.os
>
> After:
>
> text data bss dec hex filename
> 7135 12 0 7147 1beb elf/dl-sysdep.os
LGTM with a couple comments below.
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
> ---
> elf/dl-support.c | 80 +------------
> sysdeps/unix/sysv/linux/alpha/dl-auxv.h | 18 +--
> sysdeps/unix/sysv/linux/dl-parse_auxv.h | 61 ++++++++++
> sysdeps/unix/sysv/linux/dl-sysdep.c | 111 ++++++-------------
> sysdeps/unix/sysv/linux/powerpc/dl-auxv.h | 14 +--
> sysdeps/unix/sysv/linux/powerpc/dl-support.c | 4 +
> 6 files changed, 107 insertions(+), 181 deletions(-)
> create mode 100644 sysdeps/unix/sysv/linux/dl-parse_auxv.h
> create mode 100644 sysdeps/unix/sysv/linux/powerpc/dl-support.c
>
> diff --git a/elf/dl-support.c b/elf/dl-support.c
> index fb64765537..0fff62064a 100644
> --- a/elf/dl-support.c
> +++ b/elf/dl-support.c
> @@ -241,93 +241,21 @@ __rtld_lock_define_initialized_recursive (, _dl_load_tls_lock)
>
>
> #ifdef HAVE_AUX_VECTOR
> +#include <dl-parse_auxv.h>
> +
> int _dl_clktck;
>
> void
> _dl_aux_init (ElfW(auxv_t) *av)
> {
> - int seen = 0;
> - uid_t uid = 0;
> - gid_t gid = 0;
> -
> #ifdef NEED_DL_SYSINFO
> /* NB: Avoid RELATIVE relocation in static PIE. */
> GL(dl_sysinfo) = DL_SYSINFO_DEFAULT;
> #endif
>
> _dl_auxv = av;
> - for (; av->a_type != AT_NULL; ++av)
> - switch (av->a_type)
> - {
> - case AT_PAGESZ:
> - if (av->a_un.a_val != 0)
> - GLRO(dl_pagesize) = av->a_un.a_val;
> - break;
> - case AT_CLKTCK:
> - GLRO(dl_clktck) = av->a_un.a_val;
> - break;
> - case AT_PHDR:
> - GL(dl_phdr) = (const void *) av->a_un.a_val;
> - break;
> - case AT_PHNUM:
> - GL(dl_phnum) = av->a_un.a_val;
> - break;
> - case AT_PLATFORM:
> - GLRO(dl_platform) = (void *) av->a_un.a_val;
> - break;
> - case AT_HWCAP:
> - GLRO(dl_hwcap) = (unsigned long int) av->a_un.a_val;
> - break;
> - case AT_HWCAP2:
> - GLRO(dl_hwcap2) = (unsigned long int) av->a_un.a_val;
> - break;
> - case AT_FPUCW:
> - GLRO(dl_fpu_control) = av->a_un.a_val;
> - break;
> -#ifdef NEED_DL_SYSINFO
> - case AT_SYSINFO:
> - GL(dl_sysinfo) = av->a_un.a_val;
> - break;
> -#endif
> -#ifdef NEED_DL_SYSINFO_DSO
> - case AT_SYSINFO_EHDR:
> - GL(dl_sysinfo_dso) = (void *) av->a_un.a_val;
> - break;
> -#endif
> - case AT_UID:
> - uid ^= av->a_un.a_val;
> - seen |= 1;
> - break;
> - case AT_EUID:
> - uid ^= av->a_un.a_val;
> - seen |= 2;
> - break;
> - case AT_GID:
> - gid ^= av->a_un.a_val;
> - seen |= 4;
> - break;
> - case AT_EGID:
> - gid ^= av->a_un.a_val;
> - seen |= 8;
> - break;
> - case AT_SECURE:
> - seen = -1;
> - __libc_enable_secure = av->a_un.a_val;
> - __libc_enable_secure_decided = 1;
> - break;
> - case AT_RANDOM:
> - _dl_random = (void *) av->a_un.a_val;
> - break;
> - case AT_MINSIGSTKSZ:
> - _dl_minsigstacksize = av->a_un.a_val;
> - break;
> - DL_PLATFORM_AUXV
> - }
> - if (seen == 0xf)
> - {
> - __libc_enable_secure = uid != 0 || gid != 0;
> - __libc_enable_secure_decided = 1;
> - }
> + dl_parse_auxv_t auxv_values = { 0, };
> + _dl_parse_auxv (av, auxv_values);
> }
> #endif
>
> diff --git a/sysdeps/unix/sysv/linux/alpha/dl-auxv.h b/sysdeps/unix/sysv/linux/alpha/dl-auxv.h
> index 81d90da095..fcec743239 100644
> --- a/sysdeps/unix/sysv/linux/alpha/dl-auxv.h
> +++ b/sysdeps/unix/sysv/linux/alpha/dl-auxv.h
> @@ -20,16 +20,8 @@
>
> extern long __libc_alpha_cache_shape[4];
>
> -#define DL_PLATFORM_AUXV \
> - case AT_L1I_CACHESHAPE: \
> - __libc_alpha_cache_shape[0] = av->a_un.a_val; \
> - break; \
> - case AT_L1D_CACHESHAPE: \
> - __libc_alpha_cache_shape[1] = av->a_un.a_val; \
> - break; \
> - case AT_L2_CACHESHAPE: \
> - __libc_alpha_cache_shape[2] = av->a_un.a_val; \
> - break; \
> - case AT_L3_CACHESHAPE: \
> - __libc_alpha_cache_shape[3] = av->a_un.a_val; \
> - break;
> +#define DL_PLATFORM_AUXV \
> + __libc_alpha_cache_shape[0] = auxv_values[AT_L1I_CACHESHAPE]; \
> + __libc_alpha_cache_shape[1] = auxv_values[AT_L1D_CACHESHAPE]; \
> + __libc_alpha_cache_shape[2] = auxv_values[AT_L2_CACHESHAPE]; \
> + __libc_alpha_cache_shape[3] = auxv_values[AT_L3_CACHESHAPE];
> diff --git a/sysdeps/unix/sysv/linux/dl-parse_auxv.h b/sysdeps/unix/sysv/linux/dl-parse_auxv.h
> new file mode 100644
> index 0000000000..f450c6c5ce
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/dl-parse_auxv.h
> @@ -0,0 +1,61 @@
> +/* Parse the Linux auxiliary vector.
> + Copyright (C) 1995-2022 Free Software Foundation, Inc.
> + This file is part of the GNU C Library.
> +
> + The GNU C Library is free software; you can redistribute it and/or
> + modify it under the terms of the GNU Lesser General Public
> + License as published by the Free Software Foundation; either
> + version 2.1 of the License, or (at your option) any later version.
> +
> + The GNU C Library is distributed in the hope that it will be useful,
> + but WITHOUT ANY WARRANTY; without even the implied warranty of
> + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
> + Lesser General Public License for more details.
> +
> + You should have received a copy of the GNU Lesser General Public
> + License along with the GNU C Library; if not, see
> + <https://www.gnu.org/licenses/>. */
> +
> +#include <elf.h>
> +#include <entry.h>
> +#include <fpu_control.h>
> +#include <ldsodefs.h>
> +#include <link.h>
> +
> +typedef ElfW(Addr) dl_parse_auxv_t[AT_MINSIGSTKSZ + 1];
> +
> +/* Copy the auxiliary vector into AUX_VALUES and set up GLRO
> + variables. */
> +static inline
> +void _dl_parse_auxv (ElfW(auxv_t) *av, dl_parse_auxv_t auxv_values)
> +{
> + auxv_values[AT_ENTRY] = (ElfW(Addr)) ENTRY_POINT;
Extra whitespace.
> + auxv_values[AT_PAGESZ] = EXEC_PAGESIZE;
> + auxv_values[AT_FPUCW] = _FPU_DEFAULT;
> +
> + /* NB: Default to a constant CONSTANT_MINSIGSTKSZ. */
> + _Static_assert (__builtin_constant_p (CONSTANT_MINSIGSTKSZ),
> + "CONSTANT_MINSIGSTKSZ is constant");
Shouldn't it warn that CONSTANT_MINSIGSTKSZ is not a constant?
> + auxv_values[AT_MINSIGSTKSZ] = CONSTANT_MINSIGSTKSZ;
> +
> + for (; av->a_type != AT_NULL; av++)
> + if (av->a_type <= AT_MINSIGSTKSZ)
> + auxv_values[av->a_type] = av->a_un.a_val;
> +
> + GLRO(dl_pagesize) = auxv_values[AT_PAGESZ];
> + __libc_enable_secure = auxv_values[AT_SECURE];
> + GLRO(dl_platform) = (void *) auxv_values[AT_PLATFORM];
> + GLRO(dl_hwcap) = auxv_values[AT_HWCAP];
> + GLRO(dl_hwcap2) = auxv_values[AT_HWCAP2];
> + GLRO(dl_clktck) = auxv_values[AT_CLKTCK];
> + GLRO(dl_fpu_control) = auxv_values[AT_FPUCW];
> + _dl_random = (void *) auxv_values[AT_RANDOM];
> + GLRO(dl_minsigstacksize) = auxv_values[AT_MINSIGSTKSZ];
> + GLRO(dl_sysinfo_dso) = (void *) auxv_values[AT_SYSINFO_EHDR];
> +#ifdef NEED_DL_SYSINFO
I think you can now assume NEED_DL_SYSINFO is always defined.
> + if (GLRO(dl_sysinfo_dso) != NULL)
> + GLRO(dl_sysinfo) = auxv_values[AT_SYSINFO];
> +#endif
> +
> + DL_PLATFORM_AUXV
> +}
> diff --git a/sysdeps/unix/sysv/linux/dl-sysdep.c b/sysdeps/unix/sysv/linux/dl-sysdep.c
> index 2bda76b820..71cf1968b5 100644
> --- a/sysdeps/unix/sysv/linux/dl-sysdep.c
> +++ b/sysdeps/unix/sysv/linux/dl-sysdep.c
> @@ -21,13 +21,12 @@
> #include <dl-auxv.h>
> #include <dl-hwcap-check.h>
> #include <dl-osinfo.h>
> +#include <dl-parse_auxv.h>
> #include <dl-procinfo.h>
> #include <dl-tunables.h>
> #include <elf.h>
> -#include <entry.h>
> #include <errno.h>
> #include <fcntl.h>
> -#include <fpu_control.h>
> #include <ldsodefs.h>
> #include <libc-internal.h>
> #include <libintl.h>
> @@ -63,24 +62,24 @@ void *_dl_random attribute_relro = NULL;
> # define DL_STACK_END(cookie) ((void *) (cookie))
> #endif
>
> -ElfW(Addr)
> -_dl_sysdep_start (void **start_argptr,
> - void (*dl_main) (const ElfW(Phdr) *phdr, ElfW(Word) phnum,
> - ElfW(Addr) *user_entry, ElfW(auxv_t) *auxv))
> +/* Arguments passed to dl_main. */
> +struct dl_main_arguments
> {
> - const ElfW(Phdr) *phdr = NULL;
> - ElfW(Word) phnum = 0;
> + const ElfW(Phdr) *phdr;
> + ElfW(Word) phnum;
> ElfW(Addr) user_entry;
> - ElfW(auxv_t) *av;
> -#ifdef NEED_DL_SYSINFO
> - uintptr_t new_sysinfo = 0;
> -#endif
> +};
>
> - __libc_stack_end = DL_STACK_END (start_argptr);
> +/* Separate function, so that dl_main can be called without the large
> + array on the stack. */
> +static void
> +_dl_sysdep_parse_arguments (void **start_argptr,
> + struct dl_main_arguments *args)
> +{
> _dl_argc = (intptr_t) *start_argptr;
> _dl_argv = (char **) (start_argptr + 1); /* Necessary aliasing violation. */
> _environ = _dl_argv + _dl_argc + 1;
> - for (char **tmp = _environ + 1; ; ++tmp)
> + for (char **tmp = _environ; ; ++tmp)
> if (*tmp == NULL)
> {
> /* Another necessary aliasing violation. */
> @@ -88,74 +87,25 @@ _dl_sysdep_start (void **start_argptr,
> break;
> }
>
> - user_entry = (ElfW(Addr)) ENTRY_POINT;
> - GLRO(dl_platform) = NULL; /* Default to nothing known about the platform. */
> + dl_parse_auxv_t auxv_values = { 0, };
> + _dl_parse_auxv (GLRO(dl_auxv), auxv_values);
>
> - /* NB: Default to a constant CONSTANT_MINSIGSTKSZ. */
> - _Static_assert (__builtin_constant_p (CONSTANT_MINSIGSTKSZ),
> - "CONSTANT_MINSIGSTKSZ is constant");
> - GLRO(dl_minsigstacksize) = CONSTANT_MINSIGSTKSZ;
> + args->phdr = (const ElfW(Phdr) *) auxv_values[AT_PHDR];
> + args->phnum = auxv_values[AT_PHNUM];
> + args->user_entry = auxv_values[AT_ENTRY];
> +}
>
> - for (av = GLRO(dl_auxv); av->a_type != AT_NULL; av++)
> - switch (av->a_type)
> - {
> - case AT_PHDR:
> - phdr = (void *) av->a_un.a_val;
> - break;
> - case AT_PHNUM:
> - phnum = av->a_un.a_val;
> - break;
> - case AT_PAGESZ:
> - GLRO(dl_pagesize) = av->a_un.a_val;
> - break;
> - case AT_ENTRY:
> - user_entry = av->a_un.a_val;
> - break;
> - case AT_SECURE:
> - __libc_enable_secure = av->a_un.a_val;
> - break;
> - case AT_PLATFORM:
> - GLRO(dl_platform) = (void *) av->a_un.a_val;
> - break;
> - case AT_HWCAP:
> - GLRO(dl_hwcap) = (unsigned long int) av->a_un.a_val;
> - break;
> - case AT_HWCAP2:
> - GLRO(dl_hwcap2) = (unsigned long int) av->a_un.a_val;
> - break;
> - case AT_CLKTCK:
> - GLRO(dl_clktck) = av->a_un.a_val;
> - break;
> - case AT_FPUCW:
> - GLRO(dl_fpu_control) = av->a_un.a_val;
> - break;
> -#ifdef NEED_DL_SYSINFO
> - case AT_SYSINFO:
> - new_sysinfo = av->a_un.a_val;
> - break;
> -#endif
> - case AT_SYSINFO_EHDR:
> - GLRO(dl_sysinfo_dso) = (void *) av->a_un.a_val;
> - break;
> - case AT_RANDOM:
> - _dl_random = (void *) av->a_un.a_val;
> - break;
> - case AT_MINSIGSTKSZ:
> - GLRO(dl_minsigstacksize) = av->a_un.a_val;
> - break;
> - DL_PLATFORM_AUXV
> - }
> +ElfW(Addr)
> +_dl_sysdep_start (void **start_argptr,
> + void (*dl_main) (const ElfW(Phdr) *phdr, ElfW(Word) phnum,
> + ElfW(Addr) *user_entry, ElfW(auxv_t) *auxv))
> +{
> + __libc_stack_end = DL_STACK_END (start_argptr);
>
> - dl_hwcap_check ();
> + struct dl_main_arguments dl_main_args;
> + _dl_sysdep_parse_arguments (start_argptr, &dl_main_args);
>
> -#ifdef NEED_DL_SYSINFO
> - if (new_sysinfo != 0)
> - {
> - /* Only set the sysinfo value if we also have the vsyscall DSO. */
> - if (GLRO(dl_sysinfo_dso) != 0)
> - GLRO(dl_sysinfo) = new_sysinfo;
> - }
> -#endif
> + dl_hwcap_check ();
>
> __tunables_init (_environ);
>
> @@ -187,8 +137,9 @@ _dl_sysdep_start (void **start_argptr,
> if (__builtin_expect (__libc_enable_secure, 0))
> __libc_check_standard_fds ();
>
> - (*dl_main) (phdr, phnum, &user_entry, GLRO(dl_auxv));
> - return user_entry;
> + (*dl_main) (dl_main_args.phdr, dl_main_args.phnum,
> + &dl_main_args.user_entry, GLRO(dl_auxv));
> + return dl_main_args.user_entry;
> }
>
> void
> diff --git a/sysdeps/unix/sysv/linux/powerpc/dl-auxv.h b/sysdeps/unix/sysv/linux/powerpc/dl-auxv.h
> index 594371940a..ce2281cf11 100644
> --- a/sysdeps/unix/sysv/linux/powerpc/dl-auxv.h
> +++ b/sysdeps/unix/sysv/linux/powerpc/dl-auxv.h
> @@ -16,15 +16,5 @@
> License along with the GNU C Library; if not, see
> <https://www.gnu.org/licenses/>. */
>
> -#include <ldsodefs.h>
> -
> -#if IS_IN (libc) && !defined SHARED
> -int GLRO(dl_cache_line_size);
> -#endif
> -
> -/* Scan the Aux Vector for the "Data Cache Block Size" entry and assign it
> - to dl_cache_line_size. */
> -#define DL_PLATFORM_AUXV \
> - case AT_DCACHEBSIZE: \
> - GLRO(dl_cache_line_size) = av->a_un.a_val; \
> - break;
> +#define DL_PLATFORM_AUXV \
> + GLRO(dl_cache_line_size) = auxv_values[AT_DCACHEBSIZE];
> diff --git a/sysdeps/unix/sysv/linux/powerpc/dl-support.c b/sysdeps/unix/sysv/linux/powerpc/dl-support.c
> new file mode 100644
> index 0000000000..abe68a7049
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/powerpc/dl-support.c
> @@ -0,0 +1,4 @@
> +#include <elf/dl-support.c>
> +
> +/* Populated from the auxiliary vector. */
> +int _dl_cache_line_size;
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