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

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

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On 4/9/21 3:03 PM, Michael Matz wrote:
> Hello,
> 
> On Fri, 9 Apr 2021, Mark Wielaard wrote:
> 
>>> 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?
> 
> For cross the term "native" doesn't make sense, so it would seem valid to 
> simply not support that setting with a cross (not multilib) dwz.  I.e. if 
> ./native can't be executed assume cross-ness and don't support -p native.
> 

I've tried yet another variant.  Instead of trying to generate an
executable and execute it, we generate an object and test properties
using readelf.

This should no longer have the cross-build problem.

WDYT?

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 readelf output on an object generated
by 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.
...

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

	* Makefile (args.o): Add pattern rule.
	(native.o): New target.
	(clean): Update.
	* util.h (XSTR, STR): New macro.
	* args.c (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.
	* native.c: New file.

---
 Makefile | 17 ++++++++++++++++-
 args.c   | 41 ++++++++++++++++++++++++++++++++++++-----
 dwz.1    | 10 ++++++----
 native.c |  5 +++++
 util.h   |  3 +++
 5 files changed, 66 insertions(+), 10 deletions(-)

diff --git a/Makefile b/Makefile
index 02da6c4..5f0b2f0 100644
--- a/Makefile
+++ b/Makefile
@@ -20,13 +20,28 @@ OBJECTS = args.o dwz.o hashtab.o sha1.o dwarfnames.o
 LIBS=-lelf
 dwz: $(OBJECTS)
 	$(CC) $(LDFLAGS) -o $@ $^ $(LIBS)
+args.o: native.o
+NATIVE_ENDIAN=$(shell readelf -h native.o \
+	| grep Data \
+	| sed 's/.*, //;s/ endian//')
+NATIVE_POINTER_SIZE=$(shell readelf -wi native.o \
+	| grep "Pointer Size:" \
+	| sed 's/.*: *//')
+args.o: %.o: %.c
+	$(CC) $(CPPFLAGS) $(CFLAGS) -c -o $@ $< \
+	  -DNATIVE_ENDIAN=$(NATIVE_ENDIAN) \
+	  -DNATIVE_POINTER_SIZE=$(NATIVE_POINTER_SIZE)
+%.o: %.c
+	$(CC) $(CPPFLAGS) $(CFLAGS) -c -o $@ $<
 install: dwz
 	install -D dwz $(DESTDIR)$(bindir)/dwz
 	install -D -m 644 $(srcdir)/dwz.1 $(DESTDIR)$(mandir)/man1/dwz.1
 clean:
 	rm -f $(OBJECTS) *~ core* dwz $(TEST_EXECS) $(DWZ_TEST_OBJECTS) \
-	  dwz.log dwz.sum
+	  dwz.log dwz.sum native.o
 	rm -Rf testsuite-bin tmp.*
+native.o: native.c
+	$(CC) -o $@ $< -c -g
 
 PWD:=$(shell pwd -P)
 
diff --git a/args.c b/args.c
index cb11f25..e374c26 100644
--- a/args.c
+++ b/args.c
@@ -220,6 +220,15 @@ static struct option_help dwz_single_file_options_help[] =
     "Place the output in OUTFILE." }
 };
 
+#if NATIVE_ENDIAN == little
+#define NATIVE_ENDIAN_VAL __ORDER_LITTLE_ENDIAN__
+#elif NATIVE_ENDIAN == big
+#define NATIVE_ENDIAN_VAL __ORDER_LITTLE_ENDIAN__
+#else
+#define NATIVE_ENDIAN not available
+#define NATIVE_ENDIAN_VAL 0
+#endif
+
 /* Describe mult-file command line options.  */
 static struct option_help dwz_multi_file_options_help[] =
 {
@@ -236,10 +245,12 @@ 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 (NATIVE_POINTER_SIZE) "." },
+  { "e", "multifile-endian", "<l|b|auto|native>", "auto",
+    "Set endianity of multifile."
+    " Native endianity is " XSTR (NATIVE_ENDIAN) "." },
   { "j", "jobs", "<n>", "number of processors / 2",
     "Process <n> files in parallel." }
 };
@@ -385,7 +396,7 @@ 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 +661,11 @@ 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 = NATIVE_POINTER_SIZE;
+	      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 +678,21 @@ parse_args (int argc, char *argv[], bool *hardlink, const char **outfile)
 	      multifile_force_endian = 0;
 	      break;
 	    }
+	  if (strcmp (optarg, "native") == 0)
+	    {
+	      switch (NATIVE_ENDIAN_VAL)
+		{
+		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.
diff --git a/native.c b/native.c
new file mode 100644
index 0000000..398ec67
--- /dev/null
+++ b/native.c
@@ -0,0 +1,5 @@
+int
+main (void)
+{
+  return 0;
+}
diff --git a/util.h b/util.h
index 7caac06..d542942 100644
--- a/util.h
+++ b/util.h
@@ -25,6 +25,9 @@
 #define MAX(A, B) ((A) > (B) ? (A) : (B))
 #define MIN(A, B) ((A) < (B) ? (A) : (B))
 
+#define XSTR(s) STR(s)
+#define STR(s) #s
+
 #ifndef USE_GNUC
 #ifdef __GNUC__
 #define USE_GNUC 1