[MC assembler] .globl does not emit symbol if unreferenced

[DimitryAndric]

Bugzilla Link	9292
Resolution	FIXED
Resolved on	Feb 23, 2011 14:24
Version	trunk
OS	All
CC	@pwo

Extended Description

It looks like MC does not emit a global symbol into the destination
object file for a .globl directive, if the object is not referenced.

This is an unwanted optimization, since e.g. module loaders can depend
on specific symbols to always be available, so they use .globl to force
the linker to emit the symbol.

This substantially differs from GNU as's behaviour. For example,
assemble the following sample file with GNU as and clang:

.globl foo
.globl bar
mov %eax,bar

Running "readelf -s" over the object file that GNU as produces gives:

Symbol table '.symtab' contains 6 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 GLOBAL DEFAULT UND foo
5: 00000000 0 NOTYPE GLOBAL DEFAULT UND bar

Running "readelf -s" over the object file that GNU as produces gives:

Symbol table '.symtab' contains 5 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 2
3: 00000000 0 SECTION LOCAL DEFAULT 3
4: 00000000 0 NOTYPE GLOBAL DEFAULT UND bar

MC should not remove the 'foo' symbol from the table here.

[DimitryAndric]

Oops, pasto: the first symbol table (with 6 entries) was produced by
GNU as, the second table (with 5 entries) by clang r126079.

[llvmbot]

A particular annoyance is that for things like

.quad foo

gas will not produce an entry in the symbol table. I am trying to solve this without adding a lot plumbing. Lets see if it works.

[llvmbot]

Fixed in 126330.