Re: [PATCH] Add -p native and -e native

[Tom de Vries <tdevries@suse.de>]

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On 4/9/21 11:42 AM, Mark Wielaard wrote:
> On Fri, Apr 09, 2021 at 11:24:41AM +0200, Tom de Vries wrote:
>> Add option parameter native to options -p and -e.
>>
>> We determine native as the result of:
>> - -p: sizeof (void *)
>> - -e: __BYTE_ORDER__
>> when compiling using CC without CFLAGS, such that if we build dwz with -m32 on
>> x86_64 like so:
>> ...
>> $ make CFLAGS="-m32 -O2 -g" LDFLAGS=-m32
>> ...
>> and we have:
>> ...
>> $ file ./dwz
>> dwz: ELF 32-bit LSB executable, Intel 80386 <SNIP>
>> ...
>> we still have:
>> ...
>> $ ./dwz -?
>>   ...
>>   -p, --multifile-pointer-size <SIZE|auto|native>
>>                               Set pointer size of multifile, in number of bytes.
>>                               Native pointer size is 8.
>>                               Default value: auto.
>> ...
>>
>> Any comments?
> 
> Except for this narrow multilib case, doesn't this actually make it
> impossible to do a cross-arch build?

I think so, yes.  If say we'd have a cross compiler targeting arm but
running on x86_64, then the ./native exec would be for arm but we'd try
to run it on x86_64.

> I don't think this should be a
> compile time option, unless it can derived from the target
> architecture that the dwz binary is build for.

I have an updated patch that does that, AFAIU.

I just wonder whether using the term native for this functionality will
cause confusion.  Perhaps 'self' is a better way of describing this?

And now I also wonder about whether there are architectures where using
__SIZEOF_POINTER__ will be different than what is generated as dwarf
pointer size.  If so, in the previous setup I could have used CC -g,
readelf and grep to find out what is actually used and pass that as a
define to args.c

Perhaps it's a mistake to try to assign any functionality to 'native'
when crosscompiling.

Thanks,
- Tom

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Add -p native and -e native

Add option parameter native to options -p and -e.

We determine native as the result of:
- -p: __SIZEOF_POINTER__
- -e: __BYTE_ORDER__
in dwz.

2021-04-09  Tom de Vries  <tdevries@suse.de>

	* args.c (XSTR, STR, NATIVE_ENDIAN_STRING): New macro.
	(dwz_multi_file_options_help, usage): Mention -p native and -e native.
	(parse_args): Handle -p native and -e native.
	* dwz.1 (-p, -e): Mention native.

---
 args.c | 42 +++++++++++++++++++++++++++++++++++++-----
 dwz.1  | 10 ++++++----
 2 files changed, 43 insertions(+), 9 deletions(-)

diff --git a/args.c b/args.c
index 23bf1d4..5a664cf 100644
--- a/args.c
+++ b/args.c
@@ -32,6 +32,8 @@
 #include "args.h"
 
 #define IMPLIES(A, B) (!((A) && !(B)))
+#define XSTR(s) STR(s)
+#define STR(s) #s
 
 #if DEVEL
 int tracing;
@@ -220,6 +222,14 @@ static struct option_help dwz_single_file_options_help[] =
     "Place the output in OUTFILE." }
 };
 
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
+#define NATIVE_ENDIAN_STRING little
+#elif NATIVE_ENDIAN == __ORDER_BIG_ENDIAN__
+#define NATIVE_ENDIAN_STRING big
+#else
+#define NATIVE_ENDIAN_STRING not available
+#endif
+
 /* Describe mult-file command line options.  */
 static struct option_help dwz_multi_file_options_help[] =
 {
@@ -236,10 +246,12 @@ static struct option_help dwz_multi_file_options_help[] =
   { "5", "dwarf-5", NULL, NULL,
     "Emit DWARF 5 standardized supplementary object files instead of"
     " GNU extension .debug_altlink." },
-  { "p", "multifile-pointer-size", "<SIZE|auto>", "auto",
-    "Set pointer size of multifile, in number of bytes." },
-  { "e", "multifile-endian", "<l|b|auto>", "auto",
-    "Set endianity of multifile." },
+  { "p", "multifile-pointer-size", "<SIZE|auto|native>", "auto",
+     "Set pointer size of multifile, in number of bytes."
+    " Native pointer size is " XSTR (__SIZEOF_POINTER__) "." },
+  { "e", "multifile-endian", "<l|b|auto|native>", "auto",
+    "Set endianity of multifile."
+    " Native endianity is " XSTR (NATIVE_ENDIAN_STRING) "." },
   { "j", "jobs", "<n>", "number of processors / 2",
     "Process <n> files in parallel." }
 };
@@ -385,7 +397,7 @@ usage (int failing)
   FILE *stream = failing ? stderr : stdout;
   const char *header_lines[] = {
     "dwz [common options] [-h] [-m COMMONFILE] [-M NAME | -r] [-5]",
-    "    [-p <SIZE|auto>] [-e <l|b|auto>] [-j N] [FILES]",
+    "    [-p <SIZE|auto|native>] [-e <l|b|auto|native>] [-j N] [FILES]",
     "dwz [common options] -o OUTFILE FILE",
     "dwz [ -v | -? ]"
   };
@@ -650,6 +662,11 @@ parse_args (int argc, char *argv[], bool *hardlink, const char **outfile)
 	      multifile_force_ptr_size = 0;
 	      break;
 	    }
+	  if (strcmp (optarg, "native") == 0)
+	    {
+	      multifile_force_ptr_size = __SIZEOF_POINTER__;
+	      break;
+	    }
 	  l = strtoul (optarg, &end, 0);
 	  if (*end != '\0' || optarg == end || (unsigned int) l != l)
 	    error (1, 0, "invalid argument -l %s", optarg);
@@ -662,6 +679,21 @@ parse_args (int argc, char *argv[], bool *hardlink, const char **outfile)
 	      multifile_force_endian = 0;
 	      break;
 	    }
+	  if (strcmp (optarg, "native") == 0)
+	    {
+	      switch (__BYTE_ORDER__)
+		{
+		case __ORDER_LITTLE_ENDIAN__:
+		  multifile_force_endian = ELFDATA2LSB;
+		  break;
+		case __ORDER_BIG_ENDIAN__:
+		  multifile_force_endian = ELFDATA2MSB;
+		  break;
+		default:
+		  error (1, 0, "Cannot determine native endian");
+		}
+	      break;
+	    }
 	  if (strlen (optarg) != 1)
 	    error (1, 0, "invalid argument -l %s", optarg);
 	  switch (optarg[0])
diff --git a/dwz.1 b/dwz.1
index 6fec6ed..1cff329 100644
--- a/dwz.1
+++ b/dwz.1
@@ -77,13 +77,15 @@ the executable or shared library to the file named in the argument
 of the \fB-m\fR option.  Either \fB-M\fR or \fB-r\fR
 option can be specified, but not both.
 .TP
-.B \-p N \-\-multifile-pointer-size <N|auto>
+.B \-p N \-\-multifile-pointer-size <N|auto|native>
 Specify the pointer size of the multifile, in bytes.  If auto, use the
-pointer size of the files, provided they match.
+pointer size of the files, provided they match.  If native, use native pointer
+size, as specified in the help message.
 .TP
-.B \-p <l|b|auto> \-\-multifile-endian <l|b|auto>
+.B \-p <l|b|auto> \-\-multifile-endian <l|b|auto|native>
 Specify the endianity of the multifile.  If auto, use the endianity of
-the files, provided they match.
+the files, provided they match.  If native, use native endianity, as specified
+in the help message.
 .TP
 .B \-q \-\-quiet
 Silence up some of the most common messages.