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Re: [PATCH] Fix output of LD_SHOW_AUXV=1.

On 3/8/19 3:51 PM, Carlos O'Donell wrote:

On 3/8/19 7:52 AM, Stefan Liebler wrote:

Hi,

starting with commit 1616d034b61622836d3a36af53dcfca7624c844e
the output was corrupted on some platforms as _dl_procinfo
was called for every auxv entry and on some architectures like s390
all entries were represented as "AT_HWCAP".

This patch fixes the condition which determines if _dl_procinfo
is called and adjusts _dl_procinfo implementations which assumed
that they are only called for AT_HWCAP or AT_HWCAP2.

A further question is if we should always call _dl_procinfo without a
condition and let it decide if it is able to print an entry or if it
should be printed with help of the auxvars list?


This is a design question:

(a) Call machine-specific routine *after* filtering out generic options.

vs.

(b) Call machine-specific routine for *all* options and let the the
     machine-specific routine call a generic routine after it handles
     all the options it wants.

We should *always* call _dl_procinfo, and let the architectures decide
if they will handle the entry in a special way.
Exactly this is currently done as the condition is always true and e.g. for x86_64 or powerpc it works correct. The generic code (in elf/dl-sysdep.c) is printing an entry if the arch is correctly returning a non-zero-value if it is not able to print it. This is either done via auxvars information or by just printing "AT_??? ..." for unknown entries. 

Please have a look at the attached patch.
It does not require a helper function or refactoring. In fact it simplifies the patch. 
Compared to my previous patch only elf/dl-sysdep.c is changed.

Thanks,
Stefan


We need to provide a "base" function helper to allow the arches to print
the information in a generic manner if their own code decides it doesn't
want to handle it.

This would involve a refactoring of the existing code though, so I'm not
going to require it as part of fixing this for s390x.

However, if we implement (b), then the generic code doesn't need to know
what will be handled by the machine-specific routines, so I see that as
a good cleanup.

$0.02.


Okay to commit?
Once it is committed I would also backport it to glibc 2.29 release branch.


OK for master.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>


Bye,
Stefan

ChangeLog:

     * elf/dl-sysdep.c (_dl_show_auxv): Fix condition if _dl_procinfo
     is called.
     * sysdeps/unix/sysv/linux/s390/dl-procinfo.h (_dl_procinfo):
     Ignore types other than AT_HWCAP.
     * sysdeps/sparc/dl-procinfo.h (_dl_procinfo): Likewise.
     * sysdeps/unix/sysv/linux/i386/dl-procinfo.h (_dl_procinfo):
     Likewise.

20190308_ldshowauxv.patch

commit 5bbde0719d7c5fa58b0140d6fb1c6fa31a372772
Author: Stefan Liebler <stli@linux.ibm.com>
Date:   Fri Mar 8 11:18:53 2019 +0100

     Fix output of LD_SHOW_AUXV=1.
Starting with commit 1616d034b61622836d3a36af53dcfca7624c844e 
     the output was corrupted on some platforms as _dl_procinfo
     was called for every auxv entry and on some architectures like s390
     all entries were represented as "AT_HWCAP".
This patch fixes the condition which determines if _dl_procinfo 
     is called and adjusts _dl_procinfo implementations which assumed
     that they are only called for AT_HWCAP or AT_HWCAP2.


OK.


     ChangeLog:
* elf/dl-sysdep.c (_dl_show_auxv): Fix condition if _dl_procinfo 
             is called.
             * sysdeps/unix/sysv/linux/s390/dl-procinfo.h (_dl_procinfo):
             Ignore types other than AT_HWCAP.
             * sysdeps/sparc/dl-procinfo.h (_dl_procinfo): Likewise.
             * sysdeps/unix/sysv/linux/i386/dl-procinfo.h (_dl_procinfo): Likewise.

diff --git a/elf/dl-sysdep.c b/elf/dl-sysdep.c
index 5f6c679a3f..1588555651 100644
--- a/elf/dl-sysdep.c
+++ b/elf/dl-sysdep.c
@@ -329,8 +329,10 @@ _dl_show_auxv (void)
        assert (AT_IGNORE == 1);
if (av->a_type == AT_HWCAP || av->a_type == AT_HWCAP2 
-	  || AT_L1I_CACHEGEOMETRY || AT_L1D_CACHEGEOMETRY
-	  || AT_L2_CACHEGEOMETRY || AT_L3_CACHEGEOMETRY)
+	  || av->a_type == AT_L1I_CACHEGEOMETRY
+	  || av->a_type == AT_L1D_CACHEGEOMETRY
+	  || av->a_type == AT_L2_CACHEGEOMETRY
+	  || av->a_type == AT_L3_CACHEGEOMETRY)


OK. Fixes it so that we call into _dl_procinfo properly for the special cases.


  	{
  	  /* These are handled in a special way per platform.  */
  	  if (_dl_procinfo (av->a_type, av->a_un.a_val) == 0)
diff --git a/sysdeps/sparc/dl-procinfo.h b/sysdeps/sparc/dl-procinfo.h
index 282b8c5117..cc2687e99b 100644
--- a/sysdeps/sparc/dl-procinfo.h
+++ b/sysdeps/sparc/dl-procinfo.h
@@ -32,7 +32,7 @@ _dl_procinfo (unsigned int type, unsigned long int word)
    int i;
/* Fallback to unknown output mechanism. */ 
-  if (type == AT_HWCAP2)
+  if (type != AT_HWCAP)


OK.


      return -1;
_dl_printf ("AT_HWCAP: "); 
diff --git a/sysdeps/unix/sysv/linux/i386/dl-procinfo.h b/sysdeps/unix/sysv/linux/i386/dl-procinfo.h
index 22b43431bc..3aef14c6c1 100644
--- a/sysdeps/unix/sysv/linux/i386/dl-procinfo.h
+++ b/sysdeps/unix/sysv/linux/i386/dl-procinfo.h
@@ -31,7 +31,7 @@ _dl_procinfo (unsigned int type, unsigned long int word)
    int i;
/* Fallback to unknown output mechanism. */ 
-  if (type == AT_HWCAP2)
+  if (type != AT_HWCAP)


OK.


      return -1;
_dl_printf ("AT_HWCAP: "); 
diff --git a/sysdeps/unix/sysv/linux/s390/dl-procinfo.h b/sysdeps/unix/sysv/linux/s390/dl-procinfo.h
index 19329a335b..16739fd6cd 100644
--- a/sysdeps/unix/sysv/linux/s390/dl-procinfo.h
+++ b/sysdeps/unix/sysv/linux/s390/dl-procinfo.h
@@ -33,7 +33,7 @@ _dl_procinfo (unsigned int type, unsigned long int word)
    int i;
/* Fallback to unknown output mechanism. */ 
-  if (type == AT_HWCAP2)
+  if (type != AT_HWCAP)


OK.


      return -1;
_dl_printf ("AT_HWCAP: "); 

OK, verified sysdeps/unix/sysv/linux/arm/dl-procinfo.h uses a switch
statement that handles this correctly.

OK, verified sysdeps/powerpc/dl-procinfo.h uses a switch statement that
handles this correctly.




commit 988376a08d6d36ea321203b9c039db4b266609ae
Author: Stefan Liebler <stli@linux.ibm.com>
Date:   Fri Mar 8 11:18:53 2019 +0100

    Fix output of LD_SHOW_AUXV=1.
    
    Starting with commit 1616d034b61622836d3a36af53dcfca7624c844e
    the output was corrupted on some platforms as _dl_procinfo
    was called for every auxv entry and on some architectures like s390
    all entries were represented as "AT_HWCAP".
    
    This patch is removing the condition and let _dl_procinfo decide if
    an entry is printed in a platform specific or generic way.
    This patch also adjusts all _dl_procinfo implementations which assumed
    that they are only called for AT_HWCAP or AT_HWCAP2. They are now just
    returning a non-zero-value for entries which are not handled platform
    specifc.
    
    ChangeLog:
    
            * elf/dl-sysdep.c (_dl_show_auxv): Remove condition and always
            call _dl_procinfo.
            * sysdeps/unix/sysv/linux/s390/dl-procinfo.h (_dl_procinfo):
            Ignore types other than AT_HWCAP.
            * sysdeps/sparc/dl-procinfo.h (_dl_procinfo): Likewise.
            * sysdeps/unix/sysv/linux/i386/dl-procinfo.h (_dl_procinfo):
            Likewise.

diff --git a/elf/dl-sysdep.c b/elf/dl-sysdep.c
index 5f6c679a3f..5d19b100b2 100644
--- a/elf/dl-sysdep.c
+++ b/elf/dl-sysdep.c
@@ -328,14 +328,9 @@ _dl_show_auxv (void)
       assert (AT_NULL == 0);
       assert (AT_IGNORE == 1);
 
-      if (av->a_type == AT_HWCAP || av->a_type == AT_HWCAP2
-	  || AT_L1I_CACHEGEOMETRY || AT_L1D_CACHEGEOMETRY
-	  || AT_L2_CACHEGEOMETRY || AT_L3_CACHEGEOMETRY)
-	{
-	  /* These are handled in a special way per platform.  */
-	  if (_dl_procinfo (av->a_type, av->a_un.a_val) == 0)
-	    continue;
-	}
+      /* Some entries are handled in a special way per platform.  */
+      if (_dl_procinfo (av->a_type, av->a_un.a_val) == 0)
+	continue;
 
       if (idx < sizeof (auxvars) / sizeof (auxvars[0])
 	  && auxvars[idx].form != unknown)
diff --git a/sysdeps/sparc/dl-procinfo.h b/sysdeps/sparc/dl-procinfo.h
index 282b8c5117..cc2687e99b 100644
--- a/sysdeps/sparc/dl-procinfo.h
+++ b/sysdeps/sparc/dl-procinfo.h
@@ -32,7 +32,7 @@ _dl_procinfo (unsigned int type, unsigned long int word)
   int i;
 
   /* Fallback to unknown output mechanism.  */
-  if (type == AT_HWCAP2)
+  if (type != AT_HWCAP)
     return -1;
 
   _dl_printf ("AT_HWCAP:   ");
diff --git a/sysdeps/unix/sysv/linux/i386/dl-procinfo.h b/sysdeps/unix/sysv/linux/i386/dl-procinfo.h
index 22b43431bc..3aef14c6c1 100644
--- a/sysdeps/unix/sysv/linux/i386/dl-procinfo.h
+++ b/sysdeps/unix/sysv/linux/i386/dl-procinfo.h
@@ -31,7 +31,7 @@ _dl_procinfo (unsigned int type, unsigned long int word)
   int i;
 
   /* Fallback to unknown output mechanism.  */
-  if (type == AT_HWCAP2)
+  if (type != AT_HWCAP)
     return -1;
 
   _dl_printf ("AT_HWCAP:   ");
diff --git a/sysdeps/unix/sysv/linux/s390/dl-procinfo.h b/sysdeps/unix/sysv/linux/s390/dl-procinfo.h
index 19329a335b..16739fd6cd 100644
--- a/sysdeps/unix/sysv/linux/s390/dl-procinfo.h
+++ b/sysdeps/unix/sysv/linux/s390/dl-procinfo.h
@@ -33,7 +33,7 @@ _dl_procinfo (unsigned int type, unsigned long int word)
   int i;
 
   /* Fallback to unknown output mechanism.  */
-  if (type == AT_HWCAP2)
+  if (type != AT_HWCAP)
     return -1;
 
   _dl_printf ("AT_HWCAP:   ");
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