[PATCH] Prevent LTO wrappers to process a recursive execution

[PATCH] Prevent LTO wrappers to process a recursive execution

[Martin Liška]

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Hello.

To make LTO wrappers (gcc-nm, gcc-ar, gcc-ranlib) more smart, I would like to prevent execution
of the same binary by these wrapper. For LTO testing I symlink ar (nm, ranlib) to these wrappers instead
of hacking a build system to respect NM (AR, RANLIB) environment variables. The only problem with that solution
is that these wrappers recursively executes themselves as the first folder in PATH is set to the location with wrappers.

Following patch presents such recursion.

Patch can bootstrap&regtest on x86_64-linux-gnu.

Ready for trunk?
Thanks,
Martin

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From dfe0486ad7babe3d6de349001d4790684dc94bfb Mon Sep 17 00:00:00 2001
From: marxin <mliska@suse.cz>
Date: Fri, 22 Apr 2016 17:57:23 +0200
Subject: [PATCH] Prevent LTO wrappers to process a recursive execution

gcc/ChangeLog:

2016-04-22  Martin Liska  <mliska@suse.cz>

	* file-find.c (remove_prefix): New function.
	* file-find.h (remove_prefix): Declare the function.
	* gcc-ar.c (main): Skip a folder of the wrapper if
	a wrapped binary would point to the same file.
---
 gcc/file-find.c | 35 +++++++++++++++++++++++++++++++++++
 gcc/file-find.h |  1 +
 gcc/gcc-ar.c    |  8 ++++++++
 3 files changed, 44 insertions(+)

diff --git a/gcc/file-find.c b/gcc/file-find.c
index 289ef28..1066da9 100644
--- a/gcc/file-find.c
+++ b/gcc/file-find.c
@@ -208,3 +208,38 @@ prefix_from_string (const char *p, struct path_prefix *pprefix)
     }
   free (nstore);
 }
+
+void
+remove_prefix (const char *prefix, struct path_prefix *pprefix)
+{
+  struct prefix_list *remove, **prev, **remove_prev = NULL;
+  int max_len = 0;
+
+  if (pprefix->plist)
+    {
+      prev = &pprefix->plist;
+      for (struct prefix_list *pl = pprefix->plist; pl->next; pl = pl->next)
+	{
+	  if (strcmp (prefix, pl->prefix) == 0)
+	    {
+	      remove = pl;
+	      remove_prev = prev;
+	      continue;
+	    }
+
+	  int l = strlen (pl->prefix);
+	  if (l > max_len)
+	    max_len = l;
+
+	  prev = &pl;
+	}
+
+      if (remove_prev)
+	{
+	  *remove_prev = remove->next;
+	  free (remove);
+	}
+
+      pprefix->max_len = max_len;
+    }
+}
diff --git a/gcc/file-find.h b/gcc/file-find.h
index 5ad9a5f..19a4746 100644
--- a/gcc/file-find.h
+++ b/gcc/file-find.h
@@ -41,6 +41,7 @@ extern void find_file_set_debug (bool);
 extern char *find_a_file (struct path_prefix *, const char *, int);
 extern void add_prefix (struct path_prefix *, const char *);
 extern void add_prefix_begin (struct path_prefix *, const char *);
+extern void remove_prefix (const char *prefix, struct path_prefix *);
 extern void prefix_from_env (const char *, struct path_prefix *);
 extern void prefix_from_string (const char *, struct path_prefix *);
 
diff --git a/gcc/gcc-ar.c b/gcc/gcc-ar.c
index 45ba361..a02dccb 100644
--- a/gcc/gcc-ar.c
+++ b/gcc/gcc-ar.c
@@ -194,6 +194,14 @@ main (int ac, char **av)
 #ifdef CROSS_DIRECTORY_STRUCTURE
       real_exe_name = concat (target_machine, "-", PERSONALITY, NULL);
 #endif
+      /* Do not search original location in the same folder.  */
+      char *exe_folder = lrealpath (av[0]);
+      exe_folder[strlen (exe_folder) - strlen (lbasename (exe_folder))] = '\0';
+      char *location = concat (exe_folder, PERSONALITY, NULL);
+
+      if (access (location, X_OK) == 0)
+	remove_prefix (exe_folder, &path);
+
       exe_name = find_a_file (&path, real_exe_name, X_OK);
       if (!exe_name)
 	{
-- 
2.8.1

Re: [PATCH] Prevent LTO wrappers to process a recursive execution

[Andi Kleen]

Martin Liška <mliska@suse.cz> writes:
>  #endif
> +      /* Do not search original location in the same folder.  */
> +      char *exe_folder = lrealpath (av[0]);
> +      exe_folder[strlen (exe_folder) - strlen (lbasename (exe_folder))] = '\0';
> +      char *location = concat (exe_folder, PERSONALITY, NULL);

Does that really work? When the executable is found in $PATH
av[0] does not contain the full path name. But you seem to assume
it does?

-Andi

> +
> +      if (access (location, X_OK) == 0)
> +	remove_prefix (exe_folder, &path);

Re: [PATCH] Prevent LTO wrappers to process a recursive execution

[Martin Liška]

On 04/25/2016 09:30 PM, Andi Kleen wrote:
> Does that really work? When the executable is found in $PATH
> av[0] does not contain the full path name. But you seem to assume
> it does?
> 
> -Andi

Hi.

Well, it should be resolved by lrealpath. There's usage from my machine:

marxin@marxinbox:~> which nm
/home/marxin/bin/gcc2/bin/nm
marxin@marxinbox:~> strace -f -s512 nm /tmp/a.o 2>&1 | grep exec
execve("/home/marxin/bin/gcc2/bin/nm", ["nm", "/tmp/a.o"], [/* 97 vars */]) = 0
[pid  5288] execve("/home/marxin/bin/gcc2/bin/nm", ["/home/marxin/bin/gcc2/bin/nm", "--plugin", "/home/marxin/bin/gcc2/lib/gcc/x86_64-pc-linux-gnu/7.0.0/liblto_plugin.so", "/tmp/a.o"], [/* 97 vars */] <unfinished ...>
[pid  5288] <... execve resumed> )      = 0
[pid  5289] execve("/usr/bin/nm", ["/usr/bin/nm", "--plugin", "/home/marxin/bin/gcc2/lib/gcc/x86_64-pc-linux-gnu/7.0.0/liblto_plugin.so", "--plugin", "/home/marxin/bin/gcc2/lib/gcc/x86_64-pc-linux-gnu/7.0.0/liblto_plugin.so", "/tmp/a.o"], [/* 97 vars */] <unfinished ...>
[pid  5289] <... execve resumed> )      = 0

marxin@marxinbox:~> l /home/marxin/bin/gcc2/bin/ | grep nm
-rwxr-xr-x 2 marxin users  141880 Apr 26 09:53 gcc-nm*
lrwxrwxrwx 1 marxin users       6 Apr 26 09:31 nm -> gcc-nm*

Martin

Re: [PATCH] Prevent LTO wrappers to process a recursive execution

[Jeff Law]

On 04/25/2016 09:49 AM, Martin Liška wrote:
> Hello.
>
> To make LTO wrappers (gcc-nm, gcc-ar, gcc-ranlib) more smart, I would like to prevent execution
> of the same binary by these wrapper. For LTO testing I symlink ar (nm, ranlib) to these wrappers instead
> of hacking a build system to respect NM (AR, RANLIB) environment variables. The only problem with that solution
> is that these wrappers recursively executes themselves as the first folder in PATH is set to the location with wrappers.
>
> Following patch presents such recursion.
>
> Patch can bootstrap&regtest on x86_64-linux-gnu.
>
> Ready for trunk?
> Thanks,
> Martin
>
>
> 0001-Prevent-LTO-wrappers-to-process-a-recursive-executio.patch
>
>
> From dfe0486ad7babe3d6de349001d4790684dc94bfb Mon Sep 17 00:00:00 2001
> From: marxin <mliska@suse.cz>
> Date: Fri, 22 Apr 2016 17:57:23 +0200
> Subject: [PATCH] Prevent LTO wrappers to process a recursive execution
>
> gcc/ChangeLog:
>
> 2016-04-22  Martin Liska  <mliska@suse.cz>
>
> 	* file-find.c (remove_prefix): New function.
> 	* file-find.h (remove_prefix): Declare the function.
> 	* gcc-ar.c (main): Skip a folder of the wrapper if
> 	a wrapped binary would point to the same file.
Is this still something you want to pursue?  It looks pretty reasonable 
and one could make an argument that it's a good idea in and of itself.

jeff

Re: [PATCH] Prevent LTO wrappers to process a recursive execution

[Martin Liška]

On 06/23/2016 06:57 AM, Jeff Law wrote:
> Is this still something you want to pursue?  It looks pretty reasonable and one could make an argument that it's a good idea in and of itself.
> 
> jeff

Yeah, I would like to install the patch :) Can I take your reply as signal that it's accepted?

Thanks,
Martin

Re: [PATCH] Prevent LTO wrappers to process a recursive execution

[Jeff Law]

On 06/23/2016 02:23 AM, Martin Liška wrote:
> On 06/23/2016 06:57 AM, Jeff Law wrote:
>> Is this still something you want to pursue?  It looks pretty reasonable and one could make an argument that it's a good idea in and of itself.
>>
>> jeff
>
> Yeah, I would like to install the patch :) Can I take your reply as signal that it's accepted?
Yes.  It looked reasonable to me.

jeff