[PATCH 3/6] loader: Add rtld_init systemtap probe to the preloader.

[Rémi Bernon]

From: Rémi Bernon

And debugger interface as described in https://sourceware.org/git/?p=glibc.git;a=blob;f=elf/rtld-debugger-interface...
---
 loader/main.c      | 19 +++++++++++++++++
 loader/preloader.c | 51 ++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 70 insertions(+)

diff --git a/loader/main.c b/loader/main.c
index c258e025183..214343ea26f 100644
--- a/loader/main.c
+++ b/loader/main.c
@@ -33,6 +33,12 @@
 #ifdef HAVE_SYS_SYSCTL_H
 # include <sys/sysctl.h>
 #endif
+#ifdef HAVE_LINK_H
+# include <link.h>
+#endif
+#ifdef HAVE_SYS_LINK_H
+# include <sys/link.h>
+#endif

#include "main.h"

@@ -41,6 +47,16 @@ extern char **environ;
 /* the preloader will set this variable */
 const __attribute((visibility("default"))) struct wine_preload_info *wine_main_preload_info = NULL;

+#ifdef __linux__
+
+/* the preloader will set this variable */
+typedef void (*rtld_init_func)( struct link_map *map );
+__attribute((visibility("default"))) rtld_init_func wine_rtld_init = NULL;
+
+static struct link_map link_map = {0};
+
+#endif /* __linux__ */
+
 /* canonicalize path and return its directory name */
 static char *realpath_dirname( const char *name )
 {
@@ -176,6 +192,9 @@ static void *load_ntdll( char *argv0 )
 int main( int argc, char *argv[] )
 {
     void *handle;
+#ifdef __linux__
+    if (wine_rtld_init) wine_rtld_init( &link_map );
+#endif /* __linux__ */

if ((handle = load_ntdll( argv[0] )))
     {
diff --git a/loader/preloader.c b/loader/preloader.c
index d0551bae63a..49c4f0db9ad 100644
--- a/loader/preloader.c
+++ b/loader/preloader.c
@@ -85,12 +85,20 @@
 #ifdef HAVE_SYS_LINK_H
 # include <sys/link.h>
 #endif
+#ifdef HAVE_SYS_SDT_H
+# include <sys/sdt.h>
+#else
+# define STAP_PROBE2(a,b,c,d)
+# define STAP_PROBE3(a,b,c,d,e)
+#endif

#include "wine/asm.h"
 #include "main.h"

#pragma GCC visibility push(hidden)

+#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
+
 /* ELF definitions */
 #define ELF_PREFERRED_ADDRESS(loader, maplength, mapstartpref) (mapstartpref)
 #define ELF_FIXED_ADDRESS(loader, mapstart) ((void) 0)
@@ -1387,6 +1395,42 @@ static void set_process_name( int argc, char *argv[] )
     for (i = 1; i < argc; i++) argv[i] -= off;
 }

+/* GDB integration */
+extern char __executable_start;
+__attribute((visibility("default"))) void _dl_debug_state(void) {}
+__attribute((visibility("default"))) struct r_debug _r_debug =
+{
+    .r_version = 1, /* no support for r_next */
+    .r_state = RT_CONSISTENT,
+    .r_brk = (ElfW(Addr))(uintptr_t)_dl_debug_state,
+};
+
+/* sets the preloader r_debug address into DT_DEBUG */
+static void init_r_debug( struct wld_auxv *av )
+{
+    const char *l_addr = &__executable_start;
+    ElfW(Phdr) *phdr, *ph;
+    ElfW(Dyn) *dyn = NULL;
+    int phnum;
+
+    if (!(phnum = get_auxiliary( av, AT_PHNUM, 0 ))) return;
+    if (!(phdr = (void *)get_auxiliary( av, AT_PHDR, 0 ))) return;
+
+    for (ph = phdr; ph < &phdr[phnum]; ++ph) if (ph->p_type == PT_DYNAMIC) break;
+    if (ph >= &phdr[phnum]) return;
+
+    dyn = (void *)(ph->p_vaddr + l_addr);
+    while (dyn->d_tag != DT_DEBUG) dyn++;
+
+    if (dyn->d_tag == DT_DEBUG) dyn->d_un.d_ptr = (uintptr_t)&_r_debug;
+}
+
+static void rtld_init( struct link_map *map )
+{
+    STAP_PROBE2( rtld, init_start, LM_ID_BASE, &_r_debug );
+    _r_debug.r_map = map;
+    STAP_PROBE2( rtld, init_complete, LM_ID_BASE, &_r_debug );
+}

/*
  *  wld_start
@@ -1403,6 +1447,7 @@ void* wld_start( void **stack )
     struct wld_auxv new_av[8], delete_av[3], *av;
     struct wld_link_map main_binary_map, ld_so_map;
     struct wine_preload_info **wine_main_preload_info;
+    void **rtld_probe;

pargc = *stack;
     argv = (char **)pargc + 1;
@@ -1432,6 +1477,8 @@ void* wld_start( void **stack )
     dump_auxiliary( av );
 #endif

+    init_r_debug( av );
+
     /* reserve memory that Wine needs */
     if (reserve) preload_reserve( reserve );
     for (i = 0; preload_info[i].size; i++)
@@ -1475,6 +1522,10 @@ void* wld_start( void **stack )
     if (wine_main_preload_info) *wine_main_preload_info = preload_info;
     else wld_printf( "wine_main_preload_info not found\n" );

+    rtld_probe = find_symbol( &main_binary_map, "wine_rtld_init", STT_OBJECT );
+    if (rtld_probe) *rtld_probe = rtld_init;
+    else wld_printf( "wine_rtld_init not found\n" );
+
 #define SET_NEW_AV(n,type,val) new_av[n].a_type = (type); new_av[n].a_un.a_val = (val);
     SET_NEW_AV( 0, AT_PHDR, (unsigned long)main_binary_map.l_phdr );
     SET_NEW_AV( 1, AT_PHENT, sizeof(ElfW(Phdr)) );