malformed symbol

Hiroki Sato hrs at FreeBSD.org
Wed Dec 14 22:53:42 UTC 2016


Hi,

 I noticed that a simple USDT definition caused an odd error.  The
 source files in question are as follows (a complete tarball is
 attached to this email):

 sample.c:
 | #include <sys/param.h>
 | #include <stdlib.h>
 | #include <unistd.h>
 |
 | #include "sample_probes.h"
 |
 | int
 | main(void)
 | {
 |	ssize_t i;
 |	char buf[80];
 |
 |	i = read(STDIN_FILENO, buf, sizeof(buf));
 |	SAMPLE_FIRST_READ(i, buf);
 |
 |	return (0);
 | }

 sample_probes.d:
 | provider sample {
 |	probe first__read(ssize_t, char *);
 | };

 Makefile:
 | PROG=	sample
 | MAN=
 | SRCS=	sample.c sample_probes.d
 |
 |.include <bsd.prog.mk>

 Note that the program itself is useless because this is a minimal
 working example to reproduce the symptom.  It causes the following
 error:

 | dtrace -C -x nolibs -h -s sample_probes.d
 | rm -f .depend
 | echo sample.full: /usr/lib/libc.a  >> .depend
 | cc -O2 -pipe   -g -I/var/home/hrs/sample -MD  -MF.depend.sample.o -MTsample.o -std=gnu99 -fstack-protector-strong    -Qunused-arguments  -c sample.c -o sample.o
 | dtrace -C -x nolibs -G -o sample_probes.o -s sample_probes.d sample.o
 | cc -O2 -pipe -g -I/var/home/hrs/sample -std=gnu99 -fstack-protector-strong -Qunused-arguments  -o sample.full sample.o sample_probes.o
 | sample.o: In function `main':
 | /var/home/hrs/sample/sample.c:13: undefined reference to `ead'
 | cc: error: linker command failed with exit code 1 (use -v to see invocation)
 | *** Error code 1

 A symbol "read" in sample.o seems to be rewritten in the "dtrace -G"
 line.  Sample.o just after compilation of sample.c had the correct
 symbol name like the following:

 % nm sample.o
                   U __dtrace_sample___first__read
                   U __stack_chk_fail
                   U __stack_chk_guard
  0000000000000000 T main
                   U read
 % dtrace -C -x nolibs -G -o sample_probes.o -s sample_probes.d sample.o
 % nm sample.o
  0000000000000000 A __dtrace_sample___first-read
                   U __stack_chk_fail
                   U __stack_chk_guard
                   U ead
  0000000000000000 T main

 And it worked when I changed the probe name with "first__readx".

 This was reproducible on 11.x and 12.x, not on 10.x.  Could anyone
 try this and let me know if this is reproducible on your 11.x or 12.x
 box?  I guess this is a regression of symbol rewrite routine such as
 s/__/-/ in the dtrace utility while I have not investigated the
 details yet.  Or am I missing something here?

-- Hiroki
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