Re: [RFA] Incremental LTO linking part 1: simple-object bits

[Richard Biener <rguenther at suse dot de>]

On Tue, 8 May 2018, Jan Hubicka wrote:

> Hi,
> for incremental linking of LTO objects we need to copy debug sections from
> source object files into destination without renaming them from .gnu.debuglto
> into the standard debug section (because they will again be LTO debug section
> in the resulting object file).
> 
> I have discussed this with Richard on IRC and I hope it is fine to change the
> API here becuase lto-wrapper is the only user of this function.  I will send
> lto-wrapper support in separate patch.
> 
> I have lto-bootstrapped/regtested the whole incremental linking patchet on
> x86-64-linux with libbackend being incrementaly linked and also experimented
> with extra testcases and tested that debugging works on resulting cc1 binary.
> OK?

Works for me.

Richard.

> Honza
> 
> 	* simple-object.h (simple_object_copy_lto_debug_sections): Add rename
> 	parameter.
> 	* simple-object.c (handle_lto_debug_sections): Add rename parameter.
> 	(handle_lto_debug_sections_rename): New function.
> 	(handle_lto_debug_sections_norename): New function.
> 	(simple_object_copy_lto_debug_sections): Add rename parameter.
> Index: include/simple-object.h
> ===================================================================
> --- include/simple-object.h	(revision 260042)
> +++ include/simple-object.h	(working copy)
> @@ -198,12 +198,15 @@
>  simple_object_release_write (simple_object_write *);
>  
>  /* Copy LTO debug sections from SRC_OBJECT to DEST.
> +   If RENAME is true, rename LTO debug section into debug section (i.e.
> +   when producing final binary) and if it is false, keep the sections with
> +   original names (when incrementally linking).
>     If an error occurs, return the errno value in ERR and an error string.  */
>  
>  extern const char *
>  simple_object_copy_lto_debug_sections (simple_object_read *src_object,
>  				       const char *dest,
> -				       int *err);
> +				       int *err, int rename);
>  
>  #ifdef __cplusplus
>  }
> Index: libiberty/simple-object.c
> ===================================================================
> --- libiberty/simple-object.c	(revision 260042)
> +++ libiberty/simple-object.c	(working copy)
> @@ -251,12 +251,15 @@
>  }
>  
>  /* Callback to identify and rename LTO debug sections by name.
> -   Returns 1 if NAME is a LTO debug section, 0 if not.  */
> +   Returns non-NULL if NAME is a LTO debug section, NULL if not.
> +   If RENAME is true it will rename LTO debug sections to non-LTO
> +   ones.  */
>  
>  static char *
> -handle_lto_debug_sections (const char *name)
> +handle_lto_debug_sections (const char *name, int rename)
>  {
> -  char *newname = XCNEWVEC (char, strlen (name) + 1);
> +  char *newname = rename ? XCNEWVEC (char, strlen (name) + 1)
> +	  	         : xstrdup (name);
>  
>    /* ???  So we can't use .gnu.lto_ prefixed sections as the assembler
>       complains about bogus section flags.  Which means we need to arrange
> @@ -265,12 +268,14 @@
>    /* Also include corresponding reloc sections.  */
>    if (strncmp (name, ".rela", sizeof (".rela") - 1) == 0)
>      {
> -      strncpy (newname, name, sizeof (".rela") - 1);
> +      if (rename)
> +        strncpy (newname, name, sizeof (".rela") - 1);
>        name += sizeof (".rela") - 1;
>      }
>    else if (strncmp (name, ".rel", sizeof (".rel") - 1) == 0)
>      {
> -      strncpy (newname, name, sizeof (".rel") - 1);
> +      if (rename)
> +        strncpy (newname, name, sizeof (".rel") - 1);
>        name += sizeof (".rel") - 1;
>      }
>    /* ???  For now this handles both .gnu.lto_ and .gnu.debuglto_ prefixed
> @@ -277,10 +282,10 @@
>       sections.  */
>    /* Copy LTO debug sections and rename them to their non-LTO name.  */
>    if (strncmp (name, ".gnu.debuglto_", sizeof (".gnu.debuglto_") - 1) == 0)
> -    return strcat (newname, name + sizeof (".gnu.debuglto_") - 1);
> +    return rename ? strcat (newname, name + sizeof (".gnu.debuglto_") - 1) : newname;
>    else if (strncmp (name, ".gnu.lto_.debug_",
>  		    sizeof (".gnu.lto_.debug_") -1) == 0)
> -    return strcat (newname, name + sizeof (".gnu.lto_") - 1);
> +    return rename ? strcat (newname, name + sizeof (".gnu.lto_") - 1) : newname;
>    /* Copy over .note.GNU-stack section under the same name if present.  */
>    else if (strcmp (name, ".note.GNU-stack") == 0)
>      return strcpy (newname, name);
> @@ -289,14 +294,31 @@
>       COMDAT sections in objects produced by GCC.  */
>    else if (strcmp (name, ".comment") == 0)
>      return strcpy (newname, name);
> +  free (newname);
>    return NULL;
>  }
>  
> +/* Wrapper for handle_lto_debug_sections.  */
> +
> +static char *
> +handle_lto_debug_sections_rename (const char *name)
> +{
> +  return handle_lto_debug_sections (name, 1);
> +}
> +
> +/* Wrapper for handle_lto_debug_sections.  */
> +
> +static char *
> +handle_lto_debug_sections_norename (const char *name)
> +{
> +  return handle_lto_debug_sections (name, 0);
> +}
> +
>  /* Copy LTO debug sections.  */
>  
>  const char *
>  simple_object_copy_lto_debug_sections (simple_object_read *sobj,
> -				       const char *dest, int *err)
> +				       const char *dest, int *err, int rename)
>  {
>    const char *errmsg;
>    simple_object_write *dest_sobj;
> @@ -317,9 +339,10 @@
>    if (! dest_sobj)
>      return errmsg;
>  
> -  errmsg = sobj->functions->copy_lto_debug_sections (sobj, dest_sobj,
> -						     handle_lto_debug_sections,
> -						     err);
> +  errmsg = sobj->functions->copy_lto_debug_sections
> +	 	 (sobj, dest_sobj,
> +		  rename ? handle_lto_debug_sections_rename
> +			 : handle_lto_debug_sections_norename,  err);
>    if (errmsg)
>      {
>        simple_object_release_write (dest_sobj);
> 
> 

-- 
Richard Biener <rguenther@suse.de>
SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nuernberg)