* [PATCH] elf: Move elf_dynamic_do_Rel RTLD_BOOTSTRAP branches outside
@ 2022-04-18 7:37 Fangrui Song
2022-04-20 18:33 ` Adhemerval Zanella
2022-04-22 10:00 ` Andreas Schwab
0 siblings, 2 replies; 4+ messages in thread
From: Fangrui Song @ 2022-04-18 7:37 UTC (permalink / raw)
To: libc-alpha
elf_dynamic_do_Rel checks RTLD_BOOTSTRAP in several #ifdef branches.
Create an outside RTLD_BOOTSTRAP branch to simplify reasoning about the
function at the cost of a few duplicate lines.
Since dl_naudit is zero in RTLD_BOOTSTRAP code, the RTLD_BOOTSTRAP
branch can avoid _dl_audit_symbind calls to save code size (stripped
x86-64 ld.so is 672 bytes smaller).
---
elf/do-rel.h | 49 ++++++++++++++++++++++++++++---------------------
1 file changed, 28 insertions(+), 21 deletions(-)
diff --git a/elf/do-rel.h b/elf/do-rel.h
index d3e022267b..27b9b9f427 100644
--- a/elf/do-rel.h
+++ b/elf/do-rel.h
@@ -45,15 +45,35 @@ elf_dynamic_do_Rel (struct link_map *map, struct r_scope_elem *scope[],
__typeof (((ElfW(Dyn) *) 0)->d_un.d_val) nrelative,
int lazy, int skip_ifunc)
{
- const ElfW(Rel) *r = (const void *) reladdr;
+ const ElfW(Rel) *relative = (const void *) reladdr;
+ const ElfW(Rel) *r = relative + nrelative;
const ElfW(Rel) *end = (const void *) (reladdr + relsize);
ElfW(Addr) l_addr = map->l_addr;
-# if defined ELF_MACHINE_IRELATIVE && !defined RTLD_BOOTSTRAP
+ const ElfW(Sym) *const symtab
+ = (const void *) D_PTR (map, l_info[DT_SYMTAB]);
+
+#ifdef RTLD_BOOTSTRAP
+ for (; relative < r; ++relative)
+ DO_ELF_MACHINE_REL_RELATIVE (map, l_addr, relative);
+
+ const ElfW (Half) *const version
+ = (const void *) D_PTR (map, l_info[VERSYMIDX (DT_VERSYM)]);
+ for (; r < end; ++r)
+ {
+ ElfW (Half) ndx = version[ELFW (R_SYM) (r->r_info)] & 0x7fff;
+ const ElfW (Sym) *sym = &symtab[ELFW (R_SYM) (r->r_info)];
+ void *const r_addr_arg = (void *) (l_addr + r->r_offset);
+ const struct r_found_version *rversion = &map->l_versions[ndx];
+
+ elf_machine_rel (map, scope, r, sym, rversion, r_addr_arg, skip_ifunc);
+ }
+#else /* !RTLD_BOOTSTRAP */
+# if defined ELF_MACHINE_IRELATIVE
const ElfW(Rel) *r2 = NULL;
const ElfW(Rel) *end2 = NULL;
# endif
-#if (!defined DO_RELA || !defined ELF_MACHINE_PLT_REL) && !defined RTLD_BOOTSTRAP
+#if !defined DO_RELA || !defined ELF_MACHINE_PLT_REL
/* We never bind lazily during ld.so bootstrap. Unfortunately gcc is
not clever enough to see through all the function calls to realize
that. */
@@ -82,12 +102,6 @@ elf_dynamic_do_Rel (struct link_map *map, struct r_scope_elem *scope[],
else
#endif
{
- const ElfW(Sym) *const symtab =
- (const void *) D_PTR (map, l_info[DT_SYMTAB]);
- const ElfW(Rel) *relative = r;
- r += nrelative;
-
-#ifndef RTLD_BOOTSTRAP
/* This is defined in rtld.c, but nowhere in the static libc.a; make
the reference weak so static programs can still link. This
declaration cannot be done when compiling rtld.c (i.e. #ifdef
@@ -106,16 +120,10 @@ elf_dynamic_do_Rel (struct link_map *map, struct r_scope_elem *scope[],
memory_loc += l_addr... */
if (l_addr != 0)
# endif
-#endif
for (; relative < r; ++relative)
DO_ELF_MACHINE_REL_RELATIVE (map, l_addr, relative);
-#ifdef RTLD_BOOTSTRAP
- /* The dynamic linker always uses versioning. */
- assert (map->l_info[VERSYMIDX (DT_VERSYM)] != NULL);
-#else
if (map->l_info[VERSYMIDX (DT_VERSYM)])
-#endif
{
const ElfW(Half) *const version =
(const void *) D_PTR (map, l_info[VERSYMIDX (DT_VERSYM)]);
@@ -126,7 +134,7 @@ elf_dynamic_do_Rel (struct link_map *map, struct r_scope_elem *scope[],
const ElfW(Sym) *sym = &symtab[ELFW(R_SYM) (r->r_info)];
void *const r_addr_arg = (void *) (l_addr + r->r_offset);
const struct r_found_version *rversion = &map->l_versions[ndx];
-#if defined ELF_MACHINE_IRELATIVE && !defined RTLD_BOOTSTRAP
+#if defined ELF_MACHINE_IRELATIVE
if (ELFW(R_TYPE) (r->r_info) == ELF_MACHINE_IRELATIVE)
{
if (r2 == NULL)
@@ -138,7 +146,7 @@ elf_dynamic_do_Rel (struct link_map *map, struct r_scope_elem *scope[],
elf_machine_rel (map, scope, r, sym, rversion, r_addr_arg,
skip_ifunc);
-#if defined SHARED && !defined RTLD_BOOTSTRAP
+#if defined SHARED
if (ELFW(R_TYPE) (r->r_info) == ELF_MACHINE_JMP_SLOT
&& GLRO(dl_naudit) > 0)
{
@@ -151,7 +159,7 @@ elf_dynamic_do_Rel (struct link_map *map, struct r_scope_elem *scope[],
#endif
}
-#if defined ELF_MACHINE_IRELATIVE && !defined RTLD_BOOTSTRAP
+#if defined ELF_MACHINE_IRELATIVE
if (r2 != NULL)
for (; r2 <= end2; ++r2)
if (ELFW(R_TYPE) (r2->r_info) == ELF_MACHINE_IRELATIVE)
@@ -166,7 +174,6 @@ elf_dynamic_do_Rel (struct link_map *map, struct r_scope_elem *scope[],
}
#endif
}
-#ifndef RTLD_BOOTSTRAP
else
{
for (; r < end; ++r)
@@ -184,7 +191,7 @@ elf_dynamic_do_Rel (struct link_map *map, struct r_scope_elem *scope[],
# endif
elf_machine_rel (map, scope, r, sym, NULL, r_addr_arg,
skip_ifunc);
-# if defined SHARED && !defined RTLD_BOOTSTRAP
+# if defined SHARED
if (ELFW(R_TYPE) (r->r_info) == ELF_MACHINE_JMP_SLOT
&& GLRO(dl_naudit) > 0)
{
@@ -207,8 +214,8 @@ elf_dynamic_do_Rel (struct link_map *map, struct r_scope_elem *scope[],
skip_ifunc);
# endif
}
-#endif
}
+#endif /* !RTLD_BOOTSTRAP */
}
#undef elf_dynamic_do_Rel
--
2.36.0.rc0.470.gd361397f0d-goog
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] elf: Move elf_dynamic_do_Rel RTLD_BOOTSTRAP branches outside
2022-04-18 7:37 [PATCH] elf: Move elf_dynamic_do_Rel RTLD_BOOTSTRAP branches outside Fangrui Song
@ 2022-04-20 18:33 ` Adhemerval Zanella
2022-04-22 10:00 ` Andreas Schwab
1 sibling, 0 replies; 4+ messages in thread
From: Adhemerval Zanella @ 2022-04-20 18:33 UTC (permalink / raw)
To: Fangrui Song, libc-alpha
On 18/04/2022 04:37, Fangrui Song via Libc-alpha wrote:
> elf_dynamic_do_Rel checks RTLD_BOOTSTRAP in several #ifdef branches.
> Create an outside RTLD_BOOTSTRAP branch to simplify reasoning about the
> function at the cost of a few duplicate lines.
>
> Since dl_naudit is zero in RTLD_BOOTSTRAP code, the RTLD_BOOTSTRAP
> branch can avoid _dl_audit_symbind calls to save code size (stripped
> x86-64 ld.so is 672 bytes smaller).
Thanks, it does looks clear. I am seeing a code decrease on all archers,
although not a large as you are seeing (x86_64 went from 191222 to
191094).
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
> ---
> elf/do-rel.h | 49 ++++++++++++++++++++++++++++---------------------
> 1 file changed, 28 insertions(+), 21 deletions(-)
>
> diff --git a/elf/do-rel.h b/elf/do-rel.h
> index d3e022267b..27b9b9f427 100644
> --- a/elf/do-rel.h
> +++ b/elf/do-rel.h
> @@ -45,15 +45,35 @@ elf_dynamic_do_Rel (struct link_map *map, struct r_scope_elem *scope[],
> __typeof (((ElfW(Dyn) *) 0)->d_un.d_val) nrelative,
> int lazy, int skip_ifunc)
> {
> - const ElfW(Rel) *r = (const void *) reladdr;
> + const ElfW(Rel) *relative = (const void *) reladdr;
> + const ElfW(Rel) *r = relative + nrelative;
> const ElfW(Rel) *end = (const void *) (reladdr + relsize);
> ElfW(Addr) l_addr = map->l_addr;
> -# if defined ELF_MACHINE_IRELATIVE && !defined RTLD_BOOTSTRAP
> + const ElfW(Sym) *const symtab
> + = (const void *) D_PTR (map, l_info[DT_SYMTAB]);
> +
> +#ifdef RTLD_BOOTSTRAP
> + for (; relative < r; ++relative)
> + DO_ELF_MACHINE_REL_RELATIVE (map, l_addr, relative);
> +
> + const ElfW (Half) *const version
> + = (const void *) D_PTR (map, l_info[VERSYMIDX (DT_VERSYM)]);
> + for (; r < end; ++r)
> + {
> + ElfW (Half) ndx = version[ELFW (R_SYM) (r->r_info)] & 0x7fff;
> + const ElfW (Sym) *sym = &symtab[ELFW (R_SYM) (r->r_info)];
> + void *const r_addr_arg = (void *) (l_addr + r->r_offset);
> + const struct r_found_version *rversion = &map->l_versions[ndx];
> +
> + elf_machine_rel (map, scope, r, sym, rversion, r_addr_arg, skip_ifunc);
> + }
> +#else /* !RTLD_BOOTSTRAP */
> +# if defined ELF_MACHINE_IRELATIVE
> const ElfW(Rel) *r2 = NULL;
> const ElfW(Rel) *end2 = NULL;
> # endif
>
> -#if (!defined DO_RELA || !defined ELF_MACHINE_PLT_REL) && !defined RTLD_BOOTSTRAP
> +#if !defined DO_RELA || !defined ELF_MACHINE_PLT_REL
> /* We never bind lazily during ld.so bootstrap. Unfortunately gcc is
> not clever enough to see through all the function calls to realize
> that. */
> @@ -82,12 +102,6 @@ elf_dynamic_do_Rel (struct link_map *map, struct r_scope_elem *scope[],
> else
> #endif
> {
> - const ElfW(Sym) *const symtab =
> - (const void *) D_PTR (map, l_info[DT_SYMTAB]);
> - const ElfW(Rel) *relative = r;
> - r += nrelative;
> -
> -#ifndef RTLD_BOOTSTRAP
> /* This is defined in rtld.c, but nowhere in the static libc.a; make
> the reference weak so static programs can still link. This
> declaration cannot be done when compiling rtld.c (i.e. #ifdef
> @@ -106,16 +120,10 @@ elf_dynamic_do_Rel (struct link_map *map, struct r_scope_elem *scope[],
> memory_loc += l_addr... */
> if (l_addr != 0)
> # endif
> -#endif
> for (; relative < r; ++relative)
> DO_ELF_MACHINE_REL_RELATIVE (map, l_addr, relative);
>
> -#ifdef RTLD_BOOTSTRAP
> - /* The dynamic linker always uses versioning. */
> - assert (map->l_info[VERSYMIDX (DT_VERSYM)] != NULL);
> -#else
> if (map->l_info[VERSYMIDX (DT_VERSYM)])
> -#endif
> {
> const ElfW(Half) *const version =
> (const void *) D_PTR (map, l_info[VERSYMIDX (DT_VERSYM)]);
> @@ -126,7 +134,7 @@ elf_dynamic_do_Rel (struct link_map *map, struct r_scope_elem *scope[],
> const ElfW(Sym) *sym = &symtab[ELFW(R_SYM) (r->r_info)];
> void *const r_addr_arg = (void *) (l_addr + r->r_offset);
> const struct r_found_version *rversion = &map->l_versions[ndx];
> -#if defined ELF_MACHINE_IRELATIVE && !defined RTLD_BOOTSTRAP
> +#if defined ELF_MACHINE_IRELATIVE
> if (ELFW(R_TYPE) (r->r_info) == ELF_MACHINE_IRELATIVE)
> {
> if (r2 == NULL)
> @@ -138,7 +146,7 @@ elf_dynamic_do_Rel (struct link_map *map, struct r_scope_elem *scope[],
>
> elf_machine_rel (map, scope, r, sym, rversion, r_addr_arg,
> skip_ifunc);
> -#if defined SHARED && !defined RTLD_BOOTSTRAP
> +#if defined SHARED
> if (ELFW(R_TYPE) (r->r_info) == ELF_MACHINE_JMP_SLOT
> && GLRO(dl_naudit) > 0)
> {
> @@ -151,7 +159,7 @@ elf_dynamic_do_Rel (struct link_map *map, struct r_scope_elem *scope[],
> #endif
> }
>
> -#if defined ELF_MACHINE_IRELATIVE && !defined RTLD_BOOTSTRAP
> +#if defined ELF_MACHINE_IRELATIVE
> if (r2 != NULL)
> for (; r2 <= end2; ++r2)
> if (ELFW(R_TYPE) (r2->r_info) == ELF_MACHINE_IRELATIVE)
> @@ -166,7 +174,6 @@ elf_dynamic_do_Rel (struct link_map *map, struct r_scope_elem *scope[],
> }
> #endif
> }
> -#ifndef RTLD_BOOTSTRAP
> else
> {
> for (; r < end; ++r)
> @@ -184,7 +191,7 @@ elf_dynamic_do_Rel (struct link_map *map, struct r_scope_elem *scope[],
> # endif
> elf_machine_rel (map, scope, r, sym, NULL, r_addr_arg,
> skip_ifunc);
> -# if defined SHARED && !defined RTLD_BOOTSTRAP
> +# if defined SHARED
> if (ELFW(R_TYPE) (r->r_info) == ELF_MACHINE_JMP_SLOT
> && GLRO(dl_naudit) > 0)
> {
> @@ -207,8 +214,8 @@ elf_dynamic_do_Rel (struct link_map *map, struct r_scope_elem *scope[],
> skip_ifunc);
> # endif
> }
> -#endif
> }
> +#endif /* !RTLD_BOOTSTRAP */
> }
>
> #undef elf_dynamic_do_Rel
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] elf: Move elf_dynamic_do_Rel RTLD_BOOTSTRAP branches outside
2022-04-18 7:37 [PATCH] elf: Move elf_dynamic_do_Rel RTLD_BOOTSTRAP branches outside Fangrui Song
2022-04-20 18:33 ` Adhemerval Zanella
@ 2022-04-22 10:00 ` Andreas Schwab
2022-04-24 1:49 ` Fangrui Song
1 sibling, 1 reply; 4+ messages in thread
From: Andreas Schwab @ 2022-04-22 10:00 UTC (permalink / raw)
To: Fangrui Song via Libc-alpha
This breaks powerpc.
https://build.opensuse.org/package/live_build_log/home:Andreas_Schwab:glibc/glibc/p/ppc
--
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510 2552 DF73 E780 A9DA AEC1
"And now for something completely different."
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] elf: Move elf_dynamic_do_Rel RTLD_BOOTSTRAP branches outside
2022-04-22 10:00 ` Andreas Schwab
@ 2022-04-24 1:49 ` Fangrui Song
0 siblings, 0 replies; 4+ messages in thread
From: Fangrui Song @ 2022-04-24 1:49 UTC (permalink / raw)
To: Andreas Schwab; +Cc: Fangrui Song via Libc-alpha
On 2022-04-22, Andreas Schwab wrote:
>This breaks powerpc.
>
>https://build.opensuse.org/package/live_build_log/home:Andreas_Schwab:glibc/glibc/p/ppc
This is similar to the m68k breakage. This time the reordering of a GOT
load before self relocations makes ld.so fail..
https://sourceware.org/pipermail/libc-alpha/2022-April/138118.html
should fix it.
^ permalink raw reply [flat|nested] 4+ messages in thread
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2022-04-18 7:37 [PATCH] elf: Move elf_dynamic_do_Rel RTLD_BOOTSTRAP branches outside Fangrui Song
2022-04-20 18:33 ` Adhemerval Zanella
2022-04-22 10:00 ` Andreas Schwab
2022-04-24 1:49 ` Fangrui Song
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