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Cleanup shared-object support mechanics

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The former ldso-startup static library (now called ldso_so_support) is
used to spice each shared object/library with local support code for the
dynamic linker (execution of static constructors and ARM-EABI).
Therefore, the library must be statically linked to each dynamic
library.

As a result recipes for dynamic libraries must always depend on the "so"
API, which makes ldso_so_support.mk and so_support.c available
independent of "base". Additionally, ldso_so_support is also provided in
the libc API to cut the dependency early for libc/posix libraries.

Issue #3720
This commit is contained in:
Christian Helmuth
2020-04-02 08:19:34 +02:00
committed by Norman Feske
parent 589b416ca8
commit 42fddf8390
14 changed files with 95 additions and 109 deletions
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71
repos/base/src/lib/ldso/so_support.c Normal file
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@ -0,0 +1,71 @@
/**
* \brief Shared-object support code
* \author Sebastian Sumpf
* \author Christian Helmuth
* \date 2009-08-14
*
* Support code comprises hooks for execution of static constructors and
* ARM-EABI dynamic linking.
*
* The ARM cross compiler uses the __gnu_Unwind_Find_exidx hook to locate a
* 'ARM.exidx' section within a shared object. For this to work
* 'dl_unwind_find_exidx' is excuted by 'ldso', which returns the section
* address if it finds a shared object within the range of the provieded
* program counter.
*/
/*
* Copyright (C) 2009-2020 Genode Labs GmbH
*
* This file is part of the Genode OS framework, which is distributed
* under the terms of the GNU Affero General Public License version 3.
*/
#define BEG { (ld_hook) ~1U }
#define END { (ld_hook) 0 }
#define SECTION(x) __attribute__((used,section( x )))
typedef void (*ld_hook)(void);
static ld_hook _lctors_start[1] SECTION("_mark_ctors_start") = BEG;
static ld_hook _lctors_end[1] SECTION("_mark_ctors_end") = END;
/*
* '__dso_handle' needs to be defined in the main program and in each shared
* object. Because ld.lib.so is both of them, '__dso_handle' is weak here.
*/
void *__dso_handle __attribute__((__visibility__("hidden")))
__attribute__((weak)) = &__dso_handle;
/* called by dynamic linker on library startup (ld.lib.so) */
extern void _init(void) __attribute__((used,section(".init")));
extern void _init(void)
{
/* call static constructors */
for (ld_hook *func = _lctors_end; func > _lctors_start + 1; (*--func)());
}
/*
* from gcc/config/arm/unwind-arm.h
*/
typedef unsigned _Unwind_Ptr __attribute__((__mode__(__pointer__)));
/*
* Dummy for static libs, implemented in ldso for dynamic case
*/
extern _Unwind_Ptr dl_unwind_find_exidx(_Unwind_Ptr pc, int *pcount) __attribute__((weak));
extern _Unwind_Ptr dl_unwind_find_exidx(_Unwind_Ptr pc, int *pcount)
{
return 0;
}
/*
* Called from libgcc_eh.a file 'gcc/config/arm/unwind-arm.c' in function
* 'get_eit_entry'
*/
extern _Unwind_Ptr __gnu_Unwind_Find_exidx (_Unwind_Ptr pc, int *pcount)
{
return dl_unwind_find_exidx(pc, pcount);
}

38
repos/base/src/lib/ldso/startup/startup.cc
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@ -1,38 +0,0 @@
/**
* \brief Shared object startup code
* \author Sebastian Sumpf
* \date 2009-08-14
*/
/*
* Copyright (C) 2009-2017 Genode Labs GmbH
*
* This file is part of the Genode OS framework, which is distributed
* under the terms of the GNU Affero General Public License version 3.
*/
#define BEG { (ld_hook) ~1U }
#define END { (ld_hook) 0 }
#define SECTION(x) __attribute__((used,section( x )))
typedef void (*ld_hook)(void);
static ld_hook _lctors_start[1] SECTION("_mark_ctors_start") = BEG;
static ld_hook _lctors_end[1] SECTION("_mark_ctors_end") = END;
/*
* '__dso_handle' needs to be defined in the main program and in each shared
* object. Because ld.lib.so is both of them, '__dso_handle' is weak here.
*/
void *__dso_handle __attribute__((__visibility__("hidden")))
__attribute__((weak)) = &__dso_handle;
/* called by dynamic linker on library startup (ld-genode.so) */
extern "C" {
void _init(void) __attribute__((used,section(".init")));
void _init(void)
{
/* call static constructors */
for(ld_hook *func = _lctors_end; func > _lctors_start + 1; (*--func)());
}
}

48
repos/base/src/lib/ldso/startup/unwind_exidx.cc
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@ -1,48 +0,0 @@
/*
* \brief Our implementation of __gnu_Unwind_Find_exidx
* \author Sebastian Sumpf <Sebastian.Sumpf@genode-labs.com>
* \date 2010-07-05
*
* This file is used for ARM-EABI dynamic linking, only. The ARM cross-compiler
* uses this hook to locate a 'ARM.exidx' section within a shared object. For
* this to work 'dl_unwind_find_exidx' is excuted by 'ldso', which returns the
* section address if it finds a shared object within the range of the provieded
* progam counter
*/
/*
* Copyright (C) 2010-2017 Genode Labs GmbH
*
* This file is part of the Genode OS framework, which is distributed
* under the terms of the GNU Affero General Public License version 3.
*/
#include <base/log.h>
/*
* from gcc/config/arm/unwind-arm.h
*/
typedef unsigned _Unwind_Ptr __attribute__((__mode__(__pointer__)));
/*
* Implemented in ldso
* */
extern "C" _Unwind_Ptr __attribute__((weak)) dl_unwind_find_exidx(_Unwind_Ptr pc, int *pcount);
extern "C" _Unwind_Ptr dl_unwind_find_exidx(_Unwind_Ptr /* pc */, int * /* pcount */)
{
Genode::error("dl_unwind_find_exidx called");
return 0;
}
/*
* Called from libgcc_eh.a file 'gcc/config/arm/unwind-arm.c' in function
* 'get_eit_entry'
*/
extern "C" _Unwind_Ptr __gnu_Unwind_Find_exidx (_Unwind_Ptr pc, int *pcount)
{
return dl_unwind_find_exidx(pc, pcount);
}