[PATCHv1 2/2] eu-stack: add support for sysroot option

[PATCHv1 2/2] eu-stack: add support for sysroot option

[Luke Diamand]

Use the dwfl_set_sysroot() function to set the sysroot to be
used when analysing a core:

e.g.
   $ eu-stack --core core --sysroot /path/to/sysroot -e crashing_prog

Signed-off-by: Luke Diamand <ldiamand@roku.com>
---
 src/stack.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/src/stack.c b/src/stack.c
index c5f347e1..5a58cc1b 100644
--- a/src/stack.c
+++ b/src/stack.c
@@ -73,6 +73,7 @@ static int core_fd = -1;
 static Elf *core = NULL;
 static const char *exec = NULL;
 static char *debuginfo_path = NULL;
+static const char *sysroot = NULL;
 
 static const Dwfl_Callbacks proc_callbacks =
   {
@@ -554,6 +555,10 @@ parse_opt (int key, char *arg __attribute__ ((unused)),
       show_modules = true;
       break;
 
+    case 'S':
+      sysroot = arg;
+      break;
+
     case ARGP_KEY_END:
       if (core == NULL && exec != NULL)
 	argp_error (state,
@@ -587,6 +592,8 @@ parse_opt (int key, char *arg __attribute__ ((unused)),
 	  dwfl = dwfl_begin (&core_callbacks);
 	  if (dwfl == NULL)
 	    error (EXIT_BAD, 0, "dwfl_begin: %s", dwfl_errmsg (-1));
+          if (sysroot)
+            dwfl_set_sysroot(dwfl, sysroot);
 	  if (dwfl_core_file_report (dwfl, core, exec) < 0)
 	    error (EXIT_BAD, 0, "dwfl_core_file_report: %s", dwfl_errmsg (-1));
 	}
@@ -670,6 +677,8 @@ main (int argc, char **argv)
 	N_("Show at most MAXFRAMES per thread (default 256, use 0 for unlimited)"), 0 },
       { "list-modules", 'l', NULL, 0,
 	N_("Show module memory map with build-id, elf and debug files detected"), 0 },
+      { "sysroot", 'S', "sysroot", 0,
+	N_("Set the sysroot to search for libraries referenced from the core file"), 0 },
       { NULL, 0, NULL, 0, NULL, 0 }
     };
 
-- 
2.20.1

[PATCHv1 1/2] libdwfl: specify optional sysroot to search for shared libraries

[Luke Diamand]

When searching the list of modules in a core file, if the core was
generated on a different system to the current one, we need to look
in a sysroot for the various shared objects.

For example, we might be looking at a core file from an ARM system
using elfutils running on an x86 host.

This change adds a new function, dwfl_set_sysroot(), which then
gets used when searching for libraries.

Signed-off-by: Luke Diamand <ldiamand@roku.com>
---
 libdw/libdw.map    |  7 ++++++-
 libdwfl/libdwfl.h  |  5 +++++
 libdwfl/libdwflP.h |  1 +
 libdwfl/link_map.c | 25 +++++++++++++++++++++++--
 4 files changed, 35 insertions(+), 3 deletions(-)

diff --git a/libdw/libdw.map b/libdw/libdw.map
index 55482d58..43a9de2e 100644
--- a/libdw/libdw.map
+++ b/libdw/libdw.map
@@ -360,4 +360,9 @@ ELFUTILS_0.173 {
 ELFUTILS_0.175 {
   global:
     dwelf_elf_begin;
-} ELFUTILS_0.173;
\ No newline at end of file
+} ELFUTILS_0.173;
+
+ELFUTILS_0.176 {
+  global:
+    dwfl_set_sysroot;
+} ELFUTILS_0.175;
diff --git a/libdwfl/libdwfl.h b/libdwfl/libdwfl.h
index a0c1d357..c11e2f24 100644
--- a/libdwfl/libdwfl.h
+++ b/libdwfl/libdwfl.h
@@ -807,6 +807,11 @@ int dwfl_getthread_frames (Dwfl *dwfl, pid_t tid,
 bool dwfl_frame_pc (Dwfl_Frame *state, Dwarf_Addr *pc, bool *isactivation)
   __nonnull_attribute__ (1, 2);
 
+/* Set the sysroot to use when searching for shared libraries. If not
+ specified, search in the system root.  */
+void dwfl_set_sysroot (Dwfl *dwfl, const char *sysroot)
+  __nonnull_attribute__ (1);
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/libdwfl/libdwflP.h b/libdwfl/libdwflP.h
index 941a8b66..993a0e7c 100644
--- a/libdwfl/libdwflP.h
+++ b/libdwfl/libdwflP.h
@@ -138,6 +138,7 @@ struct Dwfl
   int lookup_tail_ndx;
 
   struct Dwfl_User_Core *user_core;
+  const char *sysroot;	/* sysroot, or NULL to search standard system paths */
 };
 
 #define OFFLINE_REDZONE		0x10000
diff --git a/libdwfl/link_map.c b/libdwfl/link_map.c
index 29307c74..0fae680d 100644
--- a/libdwfl/link_map.c
+++ b/libdwfl/link_map.c
@@ -388,8 +388,21 @@ report_r_debug (uint_fast8_t elfclass, uint_fast8_t elfdata,
       if (name != NULL)
 	{
 	  /* This code is mostly inlined dwfl_report_elf.  */
-	  // XXX hook for sysroot
-	  int fd = open (name, O_RDONLY);
+	  char *path_name;
+	  const char *sysroot = dwfl->sysroot;
+	  int rc;
+
+	  /* don't look in the sysroot if the path is already inside the sysroot */
+	  bool name_in_sysroot = strncmp(name, sysroot, strlen(sysroot)) == 0;
+
+	  if (!name_in_sysroot && sysroot)
+	    rc = asprintf(&path_name, "%s/%s", sysroot, name);
+	  else
+	    rc = asprintf(&path_name, "%s", name);
+	  if (unlikely(rc == -1))
+	    return release_buffer(-1);
+
+	  int fd = open (path_name, O_RDONLY);
 	  if (fd >= 0)
 	    {
 	      Elf *elf;
@@ -471,6 +484,7 @@ report_r_debug (uint_fast8_t elfclass, uint_fast8_t elfdata,
 		    close (fd);
 		}
 	    }
+          free(path_name);
 	}
 
       if (mod != NULL)
@@ -1037,3 +1051,10 @@ dwfl_link_map_report (Dwfl *dwfl, const void *auxv, size_t auxv_size,
 			 &integrated_memory_callback, &mcb, r_debug_info);
 }
 INTDEF (dwfl_link_map_report)
+
+void
+dwfl_set_sysroot (Dwfl *dwfl, const char *sysroot)
+{
+  dwfl->sysroot = sysroot;
+}
+INTDEF (dwfl_set_sysroot)
-- 
2.20.1

[PATCHv1 0/2] specify a sysroot to search when examining a core file

[Luke Diamand]

Following on from this discussion:
    https://sourceware.org/ml/elfutils-devel/2018-q4/msg00224.html

This patch adds a new API to specify a sysroot, and extends eu-stack to
use it with a new command line option.

I have been experimenting with this on various ARM-based platforms,
currently using a virt-qemu platform built from buildroot.

Luke Diamand (2):
  libdwfl: specify optional sysroot to search for shared libraries
  eu-stack: add support for sysroot option

 libdw/libdw.map    |  7 ++++++-
 libdwfl/libdwfl.h  |  5 +++++
 libdwfl/libdwflP.h |  1 +
 libdwfl/link_map.c | 25 +++++++++++++++++++++++--
 src/stack.c        |  9 +++++++++
 5 files changed, 44 insertions(+), 3 deletions(-)

-- 
2.20.1

Re: [PATCHv1 1/2] libdwfl: specify optional sysroot to search for shared libraries

[Dmitry V. Levin]

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On Sun, Jan 20, 2019 at 03:00:45PM +0000, Luke Diamand wrote:
> When searching the list of modules in a core file, if the core was
> generated on a different system to the current one, we need to look
> in a sysroot for the various shared objects.
> 
> For example, we might be looking at a core file from an ARM system
> using elfutils running on an x86 host.
> 
> This change adds a new function, dwfl_set_sysroot(), which then
> gets used when searching for libraries.
[...]
> --- a/libdwfl/link_map.c
> +++ b/libdwfl/link_map.c
> @@ -388,8 +388,21 @@ report_r_debug (uint_fast8_t elfclass, uint_fast8_t elfdata,
>        if (name != NULL)
>  	{
>  	  /* This code is mostly inlined dwfl_report_elf.  */
> -	  // XXX hook for sysroot
> -	  int fd = open (name, O_RDONLY);
> +	  char *path_name;
> +	  const char *sysroot = dwfl->sysroot;
> +	  int rc;
> +
> +	  /* don't look in the sysroot if the path is already inside the sysroot */
> +	  bool name_in_sysroot = strncmp(name, sysroot, strlen(sysroot)) == 0;

Is sysroot guaranteed to be non-NULL at this point?
If yes, is sysroot guaranteed to end with "/"?


-- 
ldv

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Re: [PATCHv1 0/2] specify a sysroot to search when examining a core file

[Mark Wielaard]

Hi Luke,

On Sun, Jan 20, 2019 at 03:00:42PM +0000, Luke Diamand wrote:
> Following on from this discussion:
>     https://sourceware.org/ml/elfutils-devel/2018-q4/msg00224.html
> 
> This patch adds a new API to specify a sysroot, and extends eu-stack to
> use it with a new command line option.
> 
> I have been experimenting with this on various ARM-based platforms,
> currently using a virt-qemu platform built from buildroot.

I like it! Thanks.
Some high level comments, before I review the actual code.

- It currently only works for resolving path names found
  in core files. It might make sense to use the same for
  other variants of dwfl_report_xxx and maybe add a
  dwfl_get_sysroot () to be used inside the find_elf
  callback. This can probably be added later though.

- eu-stack uses its own argument parser, but other tools,
  like addr2line, use the argp parser dwfl_standard_argp ().
  It would be nice to add a --sysroot argument parser there
  too that would automatically call dwfl_set_sysroot to
  make them handle --sysroot automagically.

- Is there a way to have some small testcase for this?

Cheers,

Mark

Re: [PATCHv1 0/2] specify a sysroot to search when examining a core file

[Mark Wielaard]

Hi Luke,

(BTW. Note that HTML emails will get dropped, you should get a bounce
from the mailinglist.)

On Tue, 2019-01-29 at 19:46 +0000, Luke Diamand wrote:
> Thanks for the comments on the other emails, I'll rework my patch to
> incorporate them.
> 
> I've got a small test case I've been using which uses a prebuilt ARM
> and MIPS(!) libc.so (from buildroot) and a core file. But I think in
> theory it ought to be possible to fake something up with a purely
> source code based test. Perhaps create a shared library which dumps
> core, and play around with the rpath?
> 
> Is there an existing test case you would suggest that I start from?
> 
> I'll have a look.

To test cross arch things it is sometimes just necessary to include
precompiled binaries in the test files (hopefully as small as possible
of course).

For example the tests/run-backtrace-core-<arch>.sh tests include such
pregenerated binaries:

# executable generated by:
#
# gcc -D_GNU_SOURCE -I. -I.. -I../lib -m32 -pthread -static -g \
#     -o backtrace.ppc.exec backtrace-child.c
#
# core generated by:
#
# ./backtrace.ppc.exec --gencore

tests/backtrace-subr.sh has some overly complicated code to generate a
core file for the run-backtrace-native-core.sh testcase.
For none-core, running native tests you could look at
tests/run-native-test.sh

All these are slightly fragile though.

Cheers,

Mark