Kill regexp.h

  <regexp.h> (not to be confused with <regex.h>) is an obsolete and
frankly horrible regular expression-matching API.  It was part of SVID
but was withdrawn in Issue 5 (for reference, we're on Issue 7 now).
It doesn't do anything you can't do with <regex.h>, and using it
involves defining a bunch of macros before including the header.
Moreover, the code in regexp.h that uses those macros has been buggy
since its creation (in 1996) and no one has noticed, which indicates
to me that there are no users.  (Specifically, RETURN() is used in a
whole bunch of cases where it should have been ERROR().)

Therefore, this patch stubs out the header and demotes the
implementation to compatibility symbols.  I hope this is not too late
to squeeze into glibc 2.22.  (Note: there isn't any predefined macro
to put .bss symbols in a compatibility subsection.  Using
'attribute_data_compat_section' would make the libc on disk bigger,
which seems like a move in the wrong direction.  It's only three
pointers' worth of junk, anyway...)

The ABI checker does not appear to cover these symbols; I manually
tested the effect of the patch as follows:

# glibc 2.19 (Debian)
$ readelf --dyn-syms /lib/x86_64-linux-gnu/libc.so.6 | grep -E 'advance|step|loc[12s]'
   540: 00000000000e4da0   104 FUNC    WEAK   DEFAULT   12 step@@GLIBC_2.2.5
  1364: 00000000000e4e10    84 FUNC    WEAK   DEFAULT   12 advance@@GLIBC_2.2.5
  2051: 00000000003a85e8     8 OBJECT  GLOBAL DEFAULT   32 loc1@@GLIBC_2.2.5
  2054: 00000000003a85f0     8 OBJECT  GLOBAL DEFAULT   32 loc2@@GLIBC_2.2.5
  2198: 00000000003a85f8     8 OBJECT  GLOBAL DEFAULT   32 locs@@GLIBC_2.2.5

# patched libc
$ readelf --dyn-syms ./libc.so.6 | grep -E 'advance|step|loc[12s]'
   541: 000000000011eb80   104 FUNC    WEAK   DEFAULT   12 step@GLIBC_2.2.5
  1374: 000000000011ebf0    84 FUNC    WEAK   DEFAULT   12 advance@GLIBC_2.2.5
  2065: 00000000003a35e0     8 OBJECT  GLOBAL DEFAULT   32 loc1@GLIBC_2.2.5
  2068: 00000000003a35e8     8 OBJECT  GLOBAL DEFAULT   32 loc2@GLIBC_2.2.5
  2211: 00000000003a35d8     8 OBJECT  GLOBAL DEFAULT   32 locs@GLIBC_2.2.5

$ cat test.c
#include <inttypes.h>

extern char *loc1;
extern char *loc2;
extern char *locs;
extern int step();
extern int advance();

int main(void)
{
  return (int)((intptr_t)step + (intptr_t)advance + (intptr_t)&locs + (intptr_t)&loc1 + (intptr_t)&loc2);
}

$ gcc-5 test.c; echo $?
0
$ ./testrun.sh ./a.out; echo $?
136
$ gcc-5 -nostdlib -nostartfiles csu/crt1.o csu/crti.o `gcc-5 --print-file-name=crtbegin.o` test.c libc.so.6 libc_nonshared.a -lgcc `gcc-5 --print-file-name=crtend.o` csu/crtn.o
/tmp/ccC6lyqC.o: In function `main':
test.c:(.text+0x5): undefined reference to `locs'
test.c:(.text+0xc): undefined reference to `step'
test.c:(.text+0x13): undefined reference to `loc2'
test.c:(.text+0x1c): undefined reference to `advance'
test.c:(.text+0x23): undefined reference to `loc1'
collect2: error: ld returned 1 exit status

---

N.B. I believe there *is* a past-and-future-changes copyright
assignment on file for me for glibc, but it was filed long, long
ago, if I need to do new paperwork that's OK.

zw

---
2015-07-12  Zack Weinberg  <zackw@panix.com>

	* misc/regexp.h: This interface is no longer supported.
	Remove all contents, leaving only an #error directive.
	* misc/regexp.c: Do not include regexp.h.
	(loc1, loc2, locs, step, advance): Demote to compatibility symbols.

 NEWS          |   4 ++
 misc/regexp.c |  37 +++++++----
 misc/regexp.h | 207 ++--------------------------------------------------------
 3 files changed, 34 insertions(+), 214 deletions(-)

Kill regexp.h

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