Consider this case:
	$ cat tls.s
		.text
	foo:
		.word tbase(tpoff)-12
		.word tbase(tpoff)-8
		.word tbase(tpoff)-4
		.word tbase(tpoff)+0
		.word tbase(tpoff)+4
		.word tbase(tpoff)+8
		.word tbase(tpoff)+12
		.word tbase(tpoff)
		.section        .tdata,"awT",%progbits
	tbase = . + 12
		.word -12
		.word -8
		.word -4
		.word 0
		.word 4
		.word 8
		.word 12
		.word 0
	$ ./gas/as-new -o tls.o tls.s
	$ ./binutils/readelf -Wsr -x.text tls.o

	Relocation section '.rel.text' at offset 0x128 contains 8 entries:
	 Offset     Info    Type                Sym. Value  Symbol's Name
	00000000  0000056c R_ARM_TLS_LE32         0000000c   tbase
	00000004  0000056c R_ARM_TLS_LE32         0000000c   tbase
	00000008  0000056c R_ARM_TLS_LE32         0000000c   tbase
	0000000c  0000056c R_ARM_TLS_LE32         0000000c   tbase
	00000010  0000056c R_ARM_TLS_LE32         0000000c   tbase
	00000014  0000056c R_ARM_TLS_LE32         0000000c   tbase
	00000018  0000056c R_ARM_TLS_LE32         0000000c   tbase
	0000001c  0000056c R_ARM_TLS_LE32         0000000c   tbase

	Symbol table '.symtab' contains 9 entries:
	   Num:    Value  Size Type    Bind   Vis      Ndx Name
	     0: 00000000     0 NOTYPE  LOCAL  DEFAULT  UND 
	     1: 00000000     0 SECTION LOCAL  DEFAULT    1 
	     2: 00000000     0 SECTION LOCAL  DEFAULT    3 
	     3: 00000000     0 SECTION LOCAL  DEFAULT    4 
	     4: 00000000     0 NOTYPE  LOCAL  DEFAULT    1 foo
	     5: 0000000c     0 TLS     LOCAL  DEFAULT    5 tbase
	     6: 00000000     0 SECTION LOCAL  DEFAULT    5 
	     7: 00000000     0 NOTYPE  LOCAL  DEFAULT    1 $d
	     8: 00000000     0 SECTION LOCAL  DEFAULT    6 

	Hex dump of section '.text':
	 NOTE: This section has relocations against it, but these have NOT been applied to this dump.
	  0x00000000 00000000 04000000 08000000 00000000 ................
	  0x00000010 10000000 14000000 18000000 00000000 ................

	$ 

The in-place addends (little-endian) are:
	offset 0:	0
	offset 4:	4
	offset 8:	8
	offset 12:	0
	offset 16:	16
	offset 20:	20
	offset 24:	24
	offset 28:	0
The correct addends would be:
	offset 0:	-12
	offset 4:	-8
	offset 8:	-4
	offset 12:	0
	offset 16:	4
	offset 20:	8
	offset 24:	12
	offset 24:	0

In each case where the expression was "tdata(tpoff) + offset" (with nonzero
offset), the reloc is for "tdata" but the in-place addend has the value
that would be appropriate for a reloc using the section symbol rather than
"tdata" (which starts 12 bytes into the section).  It would be kosher
enough to use these addends if it also made the relocs refer to the .tdata
section symbol rather than the "tdata" symbol.  For the cases with no
offset in the expression syntax or with explicit offset of zero, the addend
is correctly zero.